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920dae64 AT |
1 | |
2 | package Tie::File; | |
3 | require 5.005; | |
4 | use Carp ':DEFAULT', 'confess'; | |
5 | use POSIX 'SEEK_SET'; | |
6 | use Fcntl 'O_CREAT', 'O_RDWR', 'LOCK_EX', 'LOCK_SH', 'O_WRONLY', 'O_RDONLY'; | |
7 | sub O_ACCMODE () { O_RDONLY | O_RDWR | O_WRONLY } | |
8 | ||
9 | ||
10 | $VERSION = "0.97"; | |
11 | my $DEFAULT_MEMORY_SIZE = 1<<21; # 2 megabytes | |
12 | my $DEFAULT_AUTODEFER_THRESHHOLD = 3; # 3 records | |
13 | my $DEFAULT_AUTODEFER_FILELEN_THRESHHOLD = 65536; # 16 disk blocksful | |
14 | ||
15 | my %good_opt = map {$_ => 1, "-$_" => 1} | |
16 | qw(memory dw_size mode recsep discipline | |
17 | autodefer autochomp autodefer_threshhold concurrent); | |
18 | ||
19 | sub TIEARRAY { | |
20 | if (@_ % 2 != 0) { | |
21 | croak "usage: tie \@array, $_[0], filename, [option => value]..."; | |
22 | } | |
23 | my ($pack, $file, %opts) = @_; | |
24 | ||
25 | # transform '-foo' keys into 'foo' keys | |
26 | for my $key (keys %opts) { | |
27 | unless ($good_opt{$key}) { | |
28 | croak("$pack: Unrecognized option '$key'\n"); | |
29 | } | |
30 | my $okey = $key; | |
31 | if ($key =~ s/^-+//) { | |
32 | $opts{$key} = delete $opts{$okey}; | |
33 | } | |
34 | } | |
35 | ||
36 | if ($opts{concurrent}) { | |
37 | croak("$pack: concurrent access not supported yet\n"); | |
38 | } | |
39 | ||
40 | unless (defined $opts{memory}) { | |
41 | # default is the larger of the default cache size and the | |
42 | # deferred-write buffer size (if specified) | |
43 | $opts{memory} = $DEFAULT_MEMORY_SIZE; | |
44 | $opts{memory} = $opts{dw_size} | |
45 | if defined $opts{dw_size} && $opts{dw_size} > $DEFAULT_MEMORY_SIZE; | |
46 | # Dora Winifred Read | |
47 | } | |
48 | $opts{dw_size} = $opts{memory} unless defined $opts{dw_size}; | |
49 | if ($opts{dw_size} > $opts{memory}) { | |
50 | croak("$pack: dw_size may not be larger than total memory allocation\n"); | |
51 | } | |
52 | # are we in deferred-write mode? | |
53 | $opts{defer} = 0 unless defined $opts{defer}; | |
54 | $opts{deferred} = {}; # no records are presently deferred | |
55 | $opts{deferred_s} = 0; # count of total bytes in ->{deferred} | |
56 | $opts{deferred_max} = -1; # empty | |
57 | ||
58 | # What's a good way to arrange that this class can be overridden? | |
59 | $opts{cache} = Tie::File::Cache->new($opts{memory}); | |
60 | ||
61 | # autodeferment is enabled by default | |
62 | $opts{autodefer} = 1 unless defined $opts{autodefer}; | |
63 | $opts{autodeferring} = 0; # but is not initially active | |
64 | $opts{ad_history} = []; | |
65 | $opts{autodefer_threshhold} = $DEFAULT_AUTODEFER_THRESHHOLD | |
66 | unless defined $opts{autodefer_threshhold}; | |
67 | $opts{autodefer_filelen_threshhold} = $DEFAULT_AUTODEFER_FILELEN_THRESHHOLD | |
68 | unless defined $opts{autodefer_filelen_threshhold}; | |
69 | ||
70 | $opts{offsets} = [0]; | |
71 | $opts{filename} = $file; | |
72 | unless (defined $opts{recsep}) { | |
73 | $opts{recsep} = _default_recsep(); | |
74 | } | |
75 | $opts{recseplen} = length($opts{recsep}); | |
76 | if ($opts{recseplen} == 0) { | |
77 | croak "Empty record separator not supported by $pack"; | |
78 | } | |
79 | ||
80 | $opts{autochomp} = 1 unless defined $opts{autochomp}; | |
81 | ||
82 | $opts{mode} = O_CREAT|O_RDWR unless defined $opts{mode}; | |
83 | $opts{rdonly} = (($opts{mode} & O_ACCMODE) == O_RDONLY); | |
84 | $opts{sawlastrec} = undef; | |
85 | ||
86 | my $fh; | |
87 | ||
88 | if (UNIVERSAL::isa($file, 'GLOB')) { | |
89 | # We use 1 here on the theory that some systems | |
90 | # may not indicate failure if we use 0. | |
91 | # MSWin32 does not indicate failure with 0, but I don't know if | |
92 | # it will indicate failure with 1 or not. | |
93 | unless (seek $file, 1, SEEK_SET) { | |
94 | croak "$pack: your filehandle does not appear to be seekable"; | |
95 | } | |
96 | seek $file, 0, SEEK_SET # put it back | |
97 | $fh = $file; # setting binmode is the user's problem | |
98 | } elsif (ref $file) { | |
99 | croak "usage: tie \@array, $pack, filename, [option => value]..."; | |
100 | } else { | |
101 | # $fh = \do { local *FH }; # XXX this is buggy | |
102 | if ($] < 5.006) { | |
103 | # perl 5.005 and earlier don't autovivify filehandles | |
104 | require Symbol; | |
105 | $fh = Symbol::gensym(); | |
106 | } | |
107 | sysopen $fh, $file, $opts{mode}, 0666 or return; | |
108 | binmode $fh; | |
109 | ++$opts{ourfh}; | |
110 | } | |
111 | { my $ofh = select $fh; $| = 1; select $ofh } # autoflush on write | |
112 | if (defined $opts{discipline} && $] >= 5.006) { | |
113 | # This avoids a compile-time warning under 5.005 | |
114 | eval 'binmode($fh, $opts{discipline})'; | |
115 | croak $@ if $@ =~ /unknown discipline/i; | |
116 | die if $@; | |
117 | } | |
118 | $opts{fh} = $fh; | |
119 | ||
120 | bless \%opts => $pack; | |
121 | } | |
122 | ||
123 | sub FETCH { | |
124 | my ($self, $n) = @_; | |
125 | my $rec; | |
126 | ||
127 | # check the defer buffer | |
128 | $rec = $self->{deferred}{$n} if exists $self->{deferred}{$n}; | |
129 | $rec = $self->_fetch($n) unless defined $rec; | |
130 | ||
131 | # inlined _chomp1 | |
132 | substr($rec, - $self->{recseplen}) = "" | |
133 | if defined $rec && $self->{autochomp}; | |
134 | $rec; | |
135 | } | |
136 | ||
137 | # Chomp many records in-place; return nothing useful | |
138 | sub _chomp { | |
139 | my $self = shift; | |
140 | return unless $self->{autochomp}; | |
141 | if ($self->{autochomp}) { | |
142 | for (@_) { | |
143 | next unless defined; | |
144 | substr($_, - $self->{recseplen}) = ""; | |
145 | } | |
146 | } | |
147 | } | |
148 | ||
149 | # Chomp one record in-place; return modified record | |
150 | sub _chomp1 { | |
151 | my ($self, $rec) = @_; | |
152 | return $rec unless $self->{autochomp}; | |
153 | return unless defined $rec; | |
154 | substr($rec, - $self->{recseplen}) = ""; | |
155 | $rec; | |
156 | } | |
157 | ||
158 | sub _fetch { | |
159 | my ($self, $n) = @_; | |
160 | ||
161 | # check the record cache | |
162 | { my $cached = $self->{cache}->lookup($n); | |
163 | return $cached if defined $cached; | |
164 | } | |
165 | ||
166 | if ($#{$self->{offsets}} < $n) { | |
167 | return if $self->{eof}; # request for record beyond end of file | |
168 | my $o = $self->_fill_offsets_to($n); | |
169 | # If it's still undefined, there is no such record, so return 'undef' | |
170 | return unless defined $o; | |
171 | } | |
172 | ||
173 | my $fh = $self->{FH}; | |
174 | $self->_seek($n); # we can do this now that offsets is populated | |
175 | my $rec = $self->_read_record; | |
176 | ||
177 | # If we happen to have just read the first record, check to see if | |
178 | # the length of the record matches what 'tell' says. If not, Tie::File | |
179 | # won't work, and should drop dead. | |
180 | # | |
181 | # if ($n == 0 && defined($rec) && tell($self->{fh}) != length($rec)) { | |
182 | # if (defined $self->{discipline}) { | |
183 | # croak "I/O discipline $self->{discipline} not supported"; | |
184 | # } else { | |
185 | # croak "File encoding not supported"; | |
186 | # } | |
187 | # } | |
188 | ||
189 | $self->{cache}->insert($n, $rec) if defined $rec && not $self->{flushing}; | |
190 | $rec; | |
191 | } | |
192 | ||
193 | sub STORE { | |
194 | my ($self, $n, $rec) = @_; | |
195 | die "STORE called from _check_integrity!" if $DIAGNOSTIC; | |
196 | ||
197 | $self->_fixrecs($rec); | |
198 | ||
199 | if ($self->{autodefer}) { | |
200 | $self->_annotate_ad_history($n); | |
201 | } | |
202 | ||
203 | return $self->_store_deferred($n, $rec) if $self->_is_deferring; | |
204 | ||
205 | ||
206 | # We need this to decide whether the new record will fit | |
207 | # It incidentally populates the offsets table | |
208 | # Note we have to do this before we alter the cache | |
209 | # 20020324 Wait, but this DOES alter the cache. TODO BUG? | |
210 | my $oldrec = $self->_fetch($n); | |
211 | ||
212 | if (not defined $oldrec) { | |
213 | # We're storing a record beyond the end of the file | |
214 | $self->_extend_file_to($n+1); | |
215 | $oldrec = $self->{recsep}; | |
216 | } | |
217 | # return if $oldrec eq $rec; # don't bother | |
218 | my $len_diff = length($rec) - length($oldrec); | |
219 | ||
220 | # length($oldrec) here is not consistent with text mode TODO XXX BUG | |
221 | $self->_mtwrite($rec, $self->{offsets}[$n], length($oldrec)); | |
222 | $self->_oadjust([$n, 1, $rec]); | |
223 | $self->{cache}->update($n, $rec); | |
224 | } | |
225 | ||
226 | sub _store_deferred { | |
227 | my ($self, $n, $rec) = @_; | |
228 | $self->{cache}->remove($n); | |
229 | my $old_deferred = $self->{deferred}{$n}; | |
230 | ||
231 | if (defined $self->{deferred_max} && $n > $self->{deferred_max}) { | |
232 | $self->{deferred_max} = $n; | |
233 | } | |
234 | $self->{deferred}{$n} = $rec; | |
235 | ||
236 | my $len_diff = length($rec); | |
237 | $len_diff -= length($old_deferred) if defined $old_deferred; | |
238 | $self->{deferred_s} += $len_diff; | |
239 | $self->{cache}->adj_limit(-$len_diff); | |
240 | if ($self->{deferred_s} > $self->{dw_size}) { | |
241 | $self->_flush; | |
242 | } elsif ($self->_cache_too_full) { | |
243 | $self->_cache_flush; | |
244 | } | |
245 | } | |
246 | ||
247 | # Remove a single record from the deferred-write buffer without writing it | |
248 | # The record need not be present | |
249 | sub _delete_deferred { | |
250 | my ($self, $n) = @_; | |
251 | my $rec = delete $self->{deferred}{$n}; | |
252 | return unless defined $rec; | |
253 | ||
254 | if (defined $self->{deferred_max} | |
255 | && $n == $self->{deferred_max}) { | |
256 | undef $self->{deferred_max}; | |
257 | } | |
258 | ||
259 | $self->{deferred_s} -= length $rec; | |
260 | $self->{cache}->adj_limit(length $rec); | |
261 | } | |
262 | ||
263 | sub FETCHSIZE { | |
264 | my $self = shift; | |
265 | my $n = $self->{eof} ? $#{$self->{offsets}} : $self->_fill_offsets; | |
266 | ||
267 | my $top_deferred = $self->_defer_max; | |
268 | $n = $top_deferred+1 if defined $top_deferred && $n < $top_deferred+1; | |
269 | $n; | |
270 | } | |
271 | ||
272 | sub STORESIZE { | |
273 | my ($self, $len) = @_; | |
274 | ||
275 | if ($self->{autodefer}) { | |
276 | $self->_annotate_ad_history('STORESIZE'); | |
277 | } | |
278 | ||
279 | my $olen = $self->FETCHSIZE; | |
280 | return if $len == $olen; # Woo-hoo! | |
281 | ||
282 | # file gets longer | |
283 | if ($len > $olen) { | |
284 | if ($self->_is_deferring) { | |
285 | for ($olen .. $len-1) { | |
286 | $self->_store_deferred($_, $self->{recsep}); | |
287 | } | |
288 | } else { | |
289 | $self->_extend_file_to($len); | |
290 | } | |
291 | return; | |
292 | } | |
293 | ||
294 | # file gets shorter | |
295 | if ($self->_is_deferring) { | |
296 | # TODO maybe replace this with map-plus-assignment? | |
297 | for (grep $_ >= $len, keys %{$self->{deferred}}) { | |
298 | $self->_delete_deferred($_); | |
299 | } | |
300 | $self->{deferred_max} = $len-1; | |
301 | } | |
302 | ||
303 | $self->_seek($len); | |
304 | $self->_chop_file; | |
305 | $#{$self->{offsets}} = $len; | |
306 | # $self->{offsets}[0] = 0; # in case we just chopped this | |
307 | ||
308 | $self->{cache}->remove(grep $_ >= $len, $self->{cache}->ckeys); | |
309 | } | |
310 | ||
311 | ### OPTIMIZE ME | |
312 | ### It should not be necessary to do FETCHSIZE | |
313 | ### Just seek to the end of the file. | |
314 | sub PUSH { | |
315 | my $self = shift; | |
316 | $self->SPLICE($self->FETCHSIZE, scalar(@_), @_); | |
317 | ||
318 | # No need to return: | |
319 | # $self->FETCHSIZE; # because av.c takes care of this for me | |
320 | } | |
321 | ||
322 | sub POP { | |
323 | my $self = shift; | |
324 | my $size = $self->FETCHSIZE; | |
325 | return if $size == 0; | |
326 | # print STDERR "# POPPITY POP POP POP\n"; | |
327 | scalar $self->SPLICE($size-1, 1); | |
328 | } | |
329 | ||
330 | sub SHIFT { | |
331 | my $self = shift; | |
332 | scalar $self->SPLICE(0, 1); | |
333 | } | |
334 | ||
335 | sub UNSHIFT { | |
336 | my $self = shift; | |
337 | $self->SPLICE(0, 0, @_); | |
338 | # $self->FETCHSIZE; # av.c takes care of this for me | |
339 | } | |
340 | ||
341 | sub CLEAR { | |
342 | my $self = shift; | |
343 | ||
344 | if ($self->{autodefer}) { | |
345 | $self->_annotate_ad_history('CLEAR'); | |
346 | } | |
347 | ||
348 | $self->_seekb(0); | |
349 | $self->_chop_file; | |
350 | $self->{cache}->set_limit($self->{memory}); | |
351 | $self->{cache}->empty; | |
352 | @{$self->{offsets}} = (0); | |
353 | %{$self->{deferred}}= (); | |
354 | $self->{deferred_s} = 0; | |
355 | $self->{deferred_max} = -1; | |
356 | } | |
357 | ||
358 | sub EXTEND { | |
359 | my ($self, $n) = @_; | |
360 | ||
361 | # No need to pre-extend anything in this case | |
362 | return if $self->_is_deferring; | |
363 | ||
364 | $self->_fill_offsets_to($n); | |
365 | $self->_extend_file_to($n); | |
366 | } | |
367 | ||
368 | sub DELETE { | |
369 | my ($self, $n) = @_; | |
370 | ||
371 | if ($self->{autodefer}) { | |
372 | $self->_annotate_ad_history('DELETE'); | |
373 | } | |
374 | ||
375 | my $lastrec = $self->FETCHSIZE-1; | |
376 | my $rec = $self->FETCH($n); | |
377 | $self->_delete_deferred($n) if $self->_is_deferring; | |
378 | if ($n == $lastrec) { | |
379 | $self->_seek($n); | |
380 | $self->_chop_file; | |
381 | $#{$self->{offsets}}--; | |
382 | $self->{cache}->remove($n); | |
383 | # perhaps in this case I should also remove trailing null records? | |
384 | # 20020316 | |
385 | # Note that delete @a[-3..-1] deletes the records in the wrong order, | |
386 | # so we only chop the very last one out of the file. We could repair this | |
387 | # by tracking deleted records inside the object. | |
388 | } elsif ($n < $lastrec) { | |
389 | $self->STORE($n, ""); | |
390 | } | |
391 | $rec; | |
392 | } | |
393 | ||
394 | sub EXISTS { | |
395 | my ($self, $n) = @_; | |
396 | return 1 if exists $self->{deferred}{$n}; | |
397 | $n < $self->FETCHSIZE; | |
398 | } | |
399 | ||
400 | sub SPLICE { | |
401 | my $self = shift; | |
402 | ||
403 | if ($self->{autodefer}) { | |
404 | $self->_annotate_ad_history('SPLICE'); | |
405 | } | |
406 | ||
407 | $self->_flush if $self->_is_deferring; # move this up? | |
408 | if (wantarray) { | |
409 | $self->_chomp(my @a = $self->_splice(@_)); | |
410 | @a; | |
411 | } else { | |
412 | $self->_chomp1(scalar $self->_splice(@_)); | |
413 | } | |
414 | } | |
415 | ||
416 | sub DESTROY { | |
417 | my $self = shift; | |
418 | $self->flush if $self->_is_deferring; | |
419 | $self->{cache}->delink if defined $self->{cache}; # break circular link | |
420 | if ($self->{fh} and $self->{ourfh}) { | |
421 | delete $self->{ourfh}; | |
422 | close delete $self->{fh}; | |
423 | } | |
424 | } | |
425 | ||
426 | sub _splice { | |
427 | my ($self, $pos, $nrecs, @data) = @_; | |
428 | my @result; | |
429 | ||
430 | $pos = 0 unless defined $pos; | |
431 | ||
432 | # Deal with negative and other out-of-range positions | |
433 | # Also set default for $nrecs | |
434 | { | |
435 | my $oldsize = $self->FETCHSIZE; | |
436 | $nrecs = $oldsize unless defined $nrecs; | |
437 | my $oldpos = $pos; | |
438 | ||
439 | if ($pos < 0) { | |
440 | $pos += $oldsize; | |
441 | if ($pos < 0) { | |
442 | croak "Modification of non-creatable array value attempted, subscript $oldpos"; | |
443 | } | |
444 | } | |
445 | ||
446 | if ($pos > $oldsize) { | |
447 | return unless @data; | |
448 | $pos = $oldsize; # This is what perl does for normal arrays | |
449 | } | |
450 | ||
451 | # The manual is very unclear here | |
452 | if ($nrecs < 0) { | |
453 | $nrecs = $oldsize - $pos + $nrecs; | |
454 | $nrecs = 0 if $nrecs < 0; | |
455 | } | |
456 | ||
457 | # nrecs is too big---it really means "until the end" | |
458 | # 20030507 | |
459 | if ($nrecs + $pos > $oldsize) { | |
460 | $nrecs = $oldsize - $pos; | |
461 | } | |
462 | } | |
463 | ||
464 | $self->_fixrecs(@data); | |
465 | my $data = join '', @data; | |
466 | my $datalen = length $data; | |
467 | my $oldlen = 0; | |
468 | ||
469 | # compute length of data being removed | |
470 | for ($pos .. $pos+$nrecs-1) { | |
471 | last unless defined $self->_fill_offsets_to($_); | |
472 | my $rec = $self->_fetch($_); | |
473 | last unless defined $rec; | |
474 | push @result, $rec; | |
475 | ||
476 | # Why don't we just use length($rec) here? | |
477 | # Because that record might have come from the cache. _splice | |
478 | # might have been called to flush out the deferred-write records, | |
479 | # and in this case length($rec) is the length of the record to be | |
480 | # *written*, not the length of the actual record in the file. But | |
481 | # the offsets are still true. 20020322 | |
482 | $oldlen += $self->{offsets}[$_+1] - $self->{offsets}[$_] | |
483 | if defined $self->{offsets}[$_+1]; | |
484 | } | |
485 | $self->_fill_offsets_to($pos+$nrecs); | |
486 | ||
487 | # Modify the file | |
488 | $self->_mtwrite($data, $self->{offsets}[$pos], $oldlen); | |
489 | # Adjust the offsets table | |
490 | $self->_oadjust([$pos, $nrecs, @data]); | |
491 | ||
492 | { # Take this read cache stuff out into a separate function | |
493 | # You made a half-attempt to put it into _oadjust. | |
494 | # Finish something like that up eventually. | |
495 | # STORE also needs to do something similarish | |
496 | ||
497 | # update the read cache, part 1 | |
498 | # modified records | |
499 | for ($pos .. $pos+$nrecs-1) { | |
500 | my $new = $data[$_-$pos]; | |
501 | if (defined $new) { | |
502 | $self->{cache}->update($_, $new); | |
503 | } else { | |
504 | $self->{cache}->remove($_); | |
505 | } | |
506 | } | |
507 | ||
508 | # update the read cache, part 2 | |
509 | # moved records - records past the site of the change | |
510 | # need to be renumbered | |
511 | # Maybe merge this with the previous block? | |
512 | { | |
513 | my @oldkeys = grep $_ >= $pos + $nrecs, $self->{cache}->ckeys; | |
514 | my @newkeys = map $_-$nrecs+@data, @oldkeys; | |
515 | $self->{cache}->rekey(\@oldkeys, \@newkeys); | |
516 | } | |
517 | ||
518 | # Now there might be too much data in the cache, if we spliced out | |
519 | # some short records and spliced in some long ones. If so, flush | |
520 | # the cache. | |
521 | $self->_cache_flush; | |
522 | } | |
523 | ||
524 | # Yes, the return value of 'splice' *is* actually this complicated | |
525 | wantarray ? @result : @result ? $result[-1] : undef; | |
526 | } | |
527 | ||
528 | ||
529 | # write data into the file | |
530 | # $data is the data to be written. | |
531 | # it should be written at position $pos, and should overwrite | |
532 | # exactly $len of the following bytes. | |
533 | # Note that if length($data) > $len, the subsequent bytes will have to | |
534 | # be moved up, and if length($data) < $len, they will have to | |
535 | # be moved down | |
536 | sub _twrite { | |
537 | my ($self, $data, $pos, $len) = @_; | |
538 | ||
539 | unless (defined $pos) { | |
540 | die "\$pos was undefined in _twrite"; | |
541 | } | |
542 | ||
543 | my $len_diff = length($data) - $len; | |
544 | ||
545 | if ($len_diff == 0) { # Woo-hoo! | |
546 | my $fh = $self->{fh}; | |
547 | $self->_seekb($pos); | |
548 | $self->_write_record($data); | |
549 | return; # well, that was easy. | |
550 | } | |
551 | ||
552 | # the two records are of different lengths | |
553 | # our strategy here: rewrite the tail of the file, | |
554 | # reading ahead one buffer at a time | |
555 | # $bufsize is required to be at least as large as the data we're overwriting | |
556 | my $bufsize = _bufsize($len_diff); | |
557 | my ($writepos, $readpos) = ($pos, $pos+$len); | |
558 | my $next_block; | |
559 | my $more_data; | |
560 | ||
561 | # Seems like there ought to be a way to avoid the repeated code | |
562 | # and the special case here. The read(1) is also a little weird. | |
563 | # Think about this. | |
564 | do { | |
565 | $self->_seekb($readpos); | |
566 | my $br = read $self->{fh}, $next_block, $bufsize; | |
567 | $more_data = read $self->{fh}, my($dummy), 1; | |
568 | $self->_seekb($writepos); | |
569 | $self->_write_record($data); | |
570 | $readpos += $br; | |
571 | $writepos += length $data; | |
572 | $data = $next_block; | |
573 | } while $more_data; | |
574 | $self->_seekb($writepos); | |
575 | $self->_write_record($next_block); | |
576 | ||
577 | # There might be leftover data at the end of the file | |
578 | $self->_chop_file if $len_diff < 0; | |
579 | } | |
580 | ||
581 | # _iwrite(D, S, E) | |
582 | # Insert text D at position S. | |
583 | # Let C = E-S-|D|. If C < 0; die. | |
584 | # Data in [S,S+C) is copied to [S+D,S+D+C) = [S+D,E). | |
585 | # Data in [S+C = E-D, E) is returned. Data in [E, oo) is untouched. | |
586 | # | |
587 | # In a later version, don't read the entire intervening area into | |
588 | # memory at once; do the copying block by block. | |
589 | sub _iwrite { | |
590 | my $self = shift; | |
591 | my ($D, $s, $e) = @_; | |
592 | my $d = length $D; | |
593 | my $c = $e-$s-$d; | |
594 | local *FH = $self->{fh}; | |
595 | confess "Not enough space to insert $d bytes between $s and $e" | |
596 | if $c < 0; | |
597 | confess "[$s,$e) is an invalid insertion range" if $e < $s; | |
598 | ||
599 | $self->_seekb($s); | |
600 | read FH, my $buf, $e-$s; | |
601 | ||
602 | $D .= substr($buf, 0, $c, ""); | |
603 | ||
604 | $self->_seekb($s); | |
605 | $self->_write_record($D); | |
606 | ||
607 | return $buf; | |
608 | } | |
609 | ||
610 | # Like _twrite, but the data-pos-len triple may be repeated; you may | |
611 | # write several chunks. All the writing will be done in | |
612 | # one pass. Chunks SHALL be in ascending order and SHALL NOT overlap. | |
613 | sub _mtwrite { | |
614 | my $self = shift; | |
615 | my $unwritten = ""; | |
616 | my $delta = 0; | |
617 | ||
618 | @_ % 3 == 0 | |
619 | or die "Arguments to _mtwrite did not come in groups of three"; | |
620 | ||
621 | while (@_) { | |
622 | my ($data, $pos, $len) = splice @_, 0, 3; | |
623 | my $end = $pos + $len; # The OLD end of the segment to be replaced | |
624 | $data = $unwritten . $data; | |
625 | $delta -= length($unwritten); | |
626 | $unwritten = ""; | |
627 | $pos += $delta; # This is where the data goes now | |
628 | my $dlen = length $data; | |
629 | $self->_seekb($pos); | |
630 | if ($len >= $dlen) { # the data will fit | |
631 | $self->_write_record($data); | |
632 | $delta += ($dlen - $len); # everything following moves down by this much | |
633 | $data = ""; # All the data in the buffer has been written | |
634 | } else { # won't fit | |
635 | my $writable = substr($data, 0, $len - $delta, ""); | |
636 | $self->_write_record($writable); | |
637 | $delta += ($dlen - $len); # everything following moves down by this much | |
638 | } | |
639 | ||
640 | # At this point we've written some but maybe not all of the data. | |
641 | # There might be a gap to close up, or $data might still contain a | |
642 | # bunch of unwritten data that didn't fit. | |
643 | my $ndlen = length $data; | |
644 | if ($delta == 0) { | |
645 | $self->_write_record($data); | |
646 | } elsif ($delta < 0) { | |
647 | # upcopy (close up gap) | |
648 | if (@_) { | |
649 | $self->_upcopy($end, $end + $delta, $_[1] - $end); | |
650 | } else { | |
651 | $self->_upcopy($end, $end + $delta); | |
652 | } | |
653 | } else { | |
654 | # downcopy (insert data that didn't fit; replace this data in memory | |
655 | # with _later_ data that doesn't fit) | |
656 | if (@_) { | |
657 | $unwritten = $self->_downcopy($data, $end, $_[1] - $end); | |
658 | } else { | |
659 | # Make the file longer to accomodate the last segment that doesn' | |
660 | $unwritten = $self->_downcopy($data, $end); | |
661 | } | |
662 | } | |
663 | } | |
664 | } | |
665 | ||
666 | # Copy block of data of length $len from position $spos to position $dpos | |
667 | # $dpos must be <= $spos | |
668 | # | |
669 | # If $len is undefined, go all the way to the end of the file | |
670 | # and then truncate it ($spos - $dpos bytes will be removed) | |
671 | sub _upcopy { | |
672 | my $blocksize = 8192; | |
673 | my ($self, $spos, $dpos, $len) = @_; | |
674 | if ($dpos > $spos) { | |
675 | die "source ($spos) was upstream of destination ($dpos) in _upcopy"; | |
676 | } elsif ($dpos == $spos) { | |
677 | return; | |
678 | } | |
679 | ||
680 | while (! defined ($len) || $len > 0) { | |
681 | my $readsize = ! defined($len) ? $blocksize | |
682 | : $len > $blocksize ? $blocksize | |
683 | : $len; | |
684 | ||
685 | my $fh = $self->{fh}; | |
686 | $self->_seekb($spos); | |
687 | my $bytes_read = read $fh, my($data), $readsize; | |
688 | $self->_seekb($dpos); | |
689 | if ($data eq "") { | |
690 | $self->_chop_file; | |
691 | last; | |
692 | } | |
693 | $self->_write_record($data); | |
694 | $spos += $bytes_read; | |
695 | $dpos += $bytes_read; | |
696 | $len -= $bytes_read if defined $len; | |
697 | } | |
698 | } | |
699 | ||
700 | # Write $data into a block of length $len at position $pos, | |
701 | # moving everything in the block forwards to make room. | |
702 | # Instead of writing the last length($data) bytes from the block | |
703 | # (because there isn't room for them any longer) return them. | |
704 | # | |
705 | # Undefined $len means 'until the end of the file' | |
706 | sub _downcopy { | |
707 | my $blocksize = 8192; | |
708 | my ($self, $data, $pos, $len) = @_; | |
709 | my $fh = $self->{fh}; | |
710 | ||
711 | while (! defined $len || $len > 0) { | |
712 | my $readsize = ! defined($len) ? $blocksize | |
713 | : $len > $blocksize? $blocksize : $len; | |
714 | $self->_seekb($pos); | |
715 | read $fh, my($old), $readsize; | |
716 | my $last_read_was_short = length($old) < $readsize; | |
717 | $data .= $old; | |
718 | my $writable; | |
719 | if ($last_read_was_short) { | |
720 | # If last read was short, then $data now contains the entire rest | |
721 | # of the file, so there's no need to write only one block of it | |
722 | $writable = $data; | |
723 | $data = ""; | |
724 | } else { | |
725 | $writable = substr($data, 0, $readsize, ""); | |
726 | } | |
727 | last if $writable eq ""; | |
728 | $self->_seekb($pos); | |
729 | $self->_write_record($writable); | |
730 | last if $last_read_was_short && $data eq ""; | |
731 | $len -= $readsize if defined $len; | |
732 | $pos += $readsize; | |
733 | } | |
734 | return $data; | |
735 | } | |
736 | ||
737 | # Adjust the object data structures following an '_mtwrite' | |
738 | # Arguments are | |
739 | # [$pos, $nrecs, @length] items | |
740 | # indicating that $nrecs records were removed at $recpos (a record offset) | |
741 | # and replaced with records of length @length... | |
742 | # Arguments guarantee that $recpos is strictly increasing. | |
743 | # No return value | |
744 | sub _oadjust { | |
745 | my $self = shift; | |
746 | my $delta = 0; | |
747 | my $delta_recs = 0; | |
748 | my $prev_end = -1; | |
749 | my %newkeys; | |
750 | ||
751 | for (@_) { | |
752 | my ($pos, $nrecs, @data) = @$_; | |
753 | $pos += $delta_recs; | |
754 | ||
755 | # Adjust the offsets of the records after the previous batch up | |
756 | # to the first new one of this batch | |
757 | for my $i ($prev_end+2 .. $pos - 1) { | |
758 | $self->{offsets}[$i] += $delta; | |
759 | $newkey{$i} = $i + $delta_recs; | |
760 | } | |
761 | ||
762 | $prev_end = $pos + @data - 1; # last record moved on this pass | |
763 | ||
764 | # Remove the offsets for the removed records; | |
765 | # replace with the offsets for the inserted records | |
766 | my @newoff = ($self->{offsets}[$pos] + $delta); | |
767 | for my $i (0 .. $#data) { | |
768 | my $newlen = length $data[$i]; | |
769 | push @newoff, $newoff[$i] + $newlen; | |
770 | $delta += $newlen; | |
771 | } | |
772 | ||
773 | for my $i ($pos .. $pos+$nrecs-1) { | |
774 | last if $i+1 > $#{$self->{offsets}}; | |
775 | my $oldlen = $self->{offsets}[$i+1] - $self->{offsets}[$i]; | |
776 | $delta -= $oldlen; | |
777 | } | |
778 | ||
779 | # # also this data has changed, so update it in the cache | |
780 | # for (0 .. $#data) { | |
781 | # $self->{cache}->update($pos + $_, $data[$_]); | |
782 | # } | |
783 | # if ($delta_recs) { | |
784 | # my @oldkeys = grep $_ >= $pos + @data, $self->{cache}->ckeys; | |
785 | # my @newkeys = map $_ + $delta_recs, @oldkeys; | |
786 | # $self->{cache}->rekey(\@oldkeys, \@newkeys); | |
787 | # } | |
788 | ||
789 | # replace old offsets with new | |
790 | splice @{$self->{offsets}}, $pos, $nrecs+1, @newoff; | |
791 | # What if we just spliced out the end of the offsets table? | |
792 | # shouldn't we clear $self->{eof}? Test for this XXX BUG TODO | |
793 | ||
794 | $delta_recs += @data - $nrecs; # net change in total number of records | |
795 | } | |
796 | ||
797 | # The trailing records at the very end of the file | |
798 | if ($delta) { | |
799 | for my $i ($prev_end+2 .. $#{$self->{offsets}}) { | |
800 | $self->{offsets}[$i] += $delta; | |
801 | } | |
802 | } | |
803 | ||
804 | # If we scrubbed out all known offsets, regenerate the trivial table | |
805 | # that knows that the file does indeed start at 0. | |
806 | $self->{offsets}[0] = 0 unless @{$self->{offsets}}; | |
807 | # If the file got longer, the offsets table is no longer complete | |
808 | # $self->{eof} = 0 if $delta_recs > 0; | |
809 | ||
810 | # Now there might be too much data in the cache, if we spliced out | |
811 | # some short records and spliced in some long ones. If so, flush | |
812 | # the cache. | |
813 | $self->_cache_flush; | |
814 | } | |
815 | ||
816 | # If a record does not already end with the appropriate terminator | |
817 | # string, append one. | |
818 | sub _fixrecs { | |
819 | my $self = shift; | |
820 | for (@_) { | |
821 | $_ = "" unless defined $_; | |
822 | $_ .= $self->{recsep} | |
823 | unless substr($_, - $self->{recseplen}) eq $self->{recsep}; | |
824 | } | |
825 | } | |
826 | ||
827 | ||
828 | ################################################################ | |
829 | # | |
830 | # Basic read, write, and seek | |
831 | # | |
832 | ||
833 | # seek to the beginning of record #$n | |
834 | # Assumes that the offsets table is already correctly populated | |
835 | # | |
836 | # Note that $n=-1 has a special meaning here: It means the start of | |
837 | # the last known record; this may or may not be the very last record | |
838 | # in the file, depending on whether the offsets table is fully populated. | |
839 | # | |
840 | sub _seek { | |
841 | my ($self, $n) = @_; | |
842 | my $o = $self->{offsets}[$n]; | |
843 | defined($o) | |
844 | or confess("logic error: undefined offset for record $n"); | |
845 | seek $self->{fh}, $o, SEEK_SET | |
846 | or confess "Couldn't seek filehandle: $!"; # "Should never happen." | |
847 | } | |
848 | ||
849 | # seek to byte $b in the file | |
850 | sub _seekb { | |
851 | my ($self, $b) = @_; | |
852 | seek $self->{fh}, $b, SEEK_SET | |
853 | or die "Couldn't seek filehandle: $!"; # "Should never happen." | |
854 | } | |
855 | ||
856 | # populate the offsets table up to the beginning of record $n | |
857 | # return the offset of record $n | |
858 | sub _fill_offsets_to { | |
859 | my ($self, $n) = @_; | |
860 | ||
861 | return $self->{offsets}[$n] if $self->{eof}; | |
862 | ||
863 | my $fh = $self->{fh}; | |
864 | local *OFF = $self->{offsets}; | |
865 | my $rec; | |
866 | ||
867 | until ($#OFF >= $n) { | |
868 | $self->_seek(-1); # tricky -- see comment at _seek | |
869 | $rec = $self->_read_record; | |
870 | if (defined $rec) { | |
871 | push @OFF, int(tell $fh); # Tels says that int() saves memory here | |
872 | } else { | |
873 | $self->{eof} = 1; | |
874 | return; # It turns out there is no such record | |
875 | } | |
876 | } | |
877 | ||
878 | # we have now read all the records up to record n-1, | |
879 | # so we can return the offset of record n | |
880 | $OFF[$n]; | |
881 | } | |
882 | ||
883 | sub _fill_offsets { | |
884 | my ($self) = @_; | |
885 | ||
886 | my $fh = $self->{fh}; | |
887 | local *OFF = $self->{offsets}; | |
888 | ||
889 | $self->_seek(-1); # tricky -- see comment at _seek | |
890 | ||
891 | # Tels says that inlining read_record() would make this loop | |
892 | # five times faster. 20030508 | |
893 | while ( defined $self->_read_record()) { | |
894 | # int() saves us memory here | |
895 | push @OFF, int(tell $fh); | |
896 | } | |
897 | ||
898 | $self->{eof} = 1; | |
899 | $#OFF; | |
900 | } | |
901 | ||
902 | # assumes that $rec is already suitably terminated | |
903 | sub _write_record { | |
904 | my ($self, $rec) = @_; | |
905 | my $fh = $self->{fh}; | |
906 | local $\ = ""; | |
907 | print $fh $rec | |
908 | or die "Couldn't write record: $!"; # "Should never happen." | |
909 | # $self->{_written} += length($rec); | |
910 | } | |
911 | ||
912 | sub _read_record { | |
913 | my $self = shift; | |
914 | my $rec; | |
915 | { local $/ = $self->{recsep}; | |
916 | my $fh = $self->{fh}; | |
917 | $rec = <$fh>; | |
918 | } | |
919 | return unless defined $rec; | |
920 | if (substr($rec, -$self->{recseplen}) ne $self->{recsep}) { | |
921 | # improperly terminated final record --- quietly fix it. | |
922 | # my $ac = substr($rec, -$self->{recseplen}); | |
923 | # $ac =~ s/\n/\\n/g; | |
924 | $self->{sawlastrec} = 1; | |
925 | unless ($self->{rdonly}) { | |
926 | local $\ = ""; | |
927 | my $fh = $self->{fh}; | |
928 | print $fh $self->{recsep}; | |
929 | } | |
930 | $rec .= $self->{recsep}; | |
931 | } | |
932 | # $self->{_read} += length($rec) if defined $rec; | |
933 | $rec; | |
934 | } | |
935 | ||
936 | sub _rw_stats { | |
937 | my $self = shift; | |
938 | @{$self}{'_read', '_written'}; | |
939 | } | |
940 | ||
941 | ################################################################ | |
942 | # | |
943 | # Read cache management | |
944 | ||
945 | sub _cache_flush { | |
946 | my ($self) = @_; | |
947 | $self->{cache}->reduce_size_to($self->{memory} - $self->{deferred_s}); | |
948 | } | |
949 | ||
950 | sub _cache_too_full { | |
951 | my $self = shift; | |
952 | $self->{cache}->bytes + $self->{deferred_s} >= $self->{memory}; | |
953 | } | |
954 | ||
955 | ################################################################ | |
956 | # | |
957 | # File custodial services | |
958 | # | |
959 | ||
960 | ||
961 | # We have read to the end of the file and have the offsets table | |
962 | # entirely populated. Now we need to write a new record beyond | |
963 | # the end of the file. We prepare for this by writing | |
964 | # empty records into the file up to the position we want | |
965 | # | |
966 | # assumes that the offsets table already contains the offset of record $n, | |
967 | # if it exists, and extends to the end of the file if not. | |
968 | sub _extend_file_to { | |
969 | my ($self, $n) = @_; | |
970 | $self->_seek(-1); # position after the end of the last record | |
971 | my $pos = $self->{offsets}[-1]; | |
972 | ||
973 | # the offsets table has one entry more than the total number of records | |
974 | my $extras = $n - $#{$self->{offsets}}; | |
975 | ||
976 | # Todo : just use $self->{recsep} x $extras here? | |
977 | while ($extras-- > 0) { | |
978 | $self->_write_record($self->{recsep}); | |
979 | push @{$self->{offsets}}, int(tell $self->{fh}); | |
980 | } | |
981 | } | |
982 | ||
983 | # Truncate the file at the current position | |
984 | sub _chop_file { | |
985 | my $self = shift; | |
986 | truncate $self->{fh}, tell($self->{fh}); | |
987 | } | |
988 | ||
989 | ||
990 | # compute the size of a buffer suitable for moving | |
991 | # all the data in a file forward $n bytes | |
992 | # ($n may be negative) | |
993 | # The result should be at least $n. | |
994 | sub _bufsize { | |
995 | my $n = shift; | |
996 | return 8192 if $n <= 0; | |
997 | my $b = $n & ~8191; | |
998 | $b += 8192 if $n & 8191; | |
999 | $b; | |
1000 | } | |
1001 | ||
1002 | ################################################################ | |
1003 | # | |
1004 | # Miscellaneous public methods | |
1005 | # | |
1006 | ||
1007 | # Lock the file | |
1008 | sub flock { | |
1009 | my ($self, $op) = @_; | |
1010 | unless (@_ <= 3) { | |
1011 | my $pack = ref $self; | |
1012 | croak "Usage: $pack\->flock([OPERATION])"; | |
1013 | } | |
1014 | my $fh = $self->{fh}; | |
1015 | $op = LOCK_EX unless defined $op; | |
1016 | my $locked = flock $fh, $op; | |
1017 | ||
1018 | if ($locked && ($op & (LOCK_EX | LOCK_SH))) { | |
1019 | # If you're locking the file, then presumably it's because | |
1020 | # there might have been a write access by another process. | |
1021 | # In that case, the read cache contents and the offsets table | |
1022 | # might be invalid, so discard them. 20030508 | |
1023 | $self->{offsets} = [0]; | |
1024 | $self->{cache}->empty; | |
1025 | } | |
1026 | ||
1027 | $locked; | |
1028 | } | |
1029 | ||
1030 | # Get/set autochomp option | |
1031 | sub autochomp { | |
1032 | my $self = shift; | |
1033 | if (@_) { | |
1034 | my $old = $self->{autochomp}; | |
1035 | $self->{autochomp} = shift; | |
1036 | $old; | |
1037 | } else { | |
1038 | $self->{autochomp}; | |
1039 | } | |
1040 | } | |
1041 | ||
1042 | # Get offset table entries; returns offset of nth record | |
1043 | sub offset { | |
1044 | my ($self, $n) = @_; | |
1045 | ||
1046 | if ($#{$self->{offsets}} < $n) { | |
1047 | return if $self->{eof}; # request for record beyond the end of file | |
1048 | my $o = $self->_fill_offsets_to($n); | |
1049 | # If it's still undefined, there is no such record, so return 'undef' | |
1050 | return unless defined $o; | |
1051 | } | |
1052 | ||
1053 | $self->{offsets}[$n]; | |
1054 | } | |
1055 | ||
1056 | sub discard_offsets { | |
1057 | my $self = shift; | |
1058 | $self->{offsets} = [0]; | |
1059 | } | |
1060 | ||
1061 | ################################################################ | |
1062 | # | |
1063 | # Matters related to deferred writing | |
1064 | # | |
1065 | ||
1066 | # Defer writes | |
1067 | sub defer { | |
1068 | my $self = shift; | |
1069 | $self->_stop_autodeferring; | |
1070 | @{$self->{ad_history}} = (); | |
1071 | $self->{defer} = 1; | |
1072 | } | |
1073 | ||
1074 | # Flush deferred writes | |
1075 | # | |
1076 | # This could be better optimized to write the file in one pass, instead | |
1077 | # of one pass per block of records. But that will require modifications | |
1078 | # to _twrite, so I should have a good _twrite test suite first. | |
1079 | sub flush { | |
1080 | my $self = shift; | |
1081 | ||
1082 | $self->_flush; | |
1083 | $self->{defer} = 0; | |
1084 | } | |
1085 | ||
1086 | sub _old_flush { | |
1087 | my $self = shift; | |
1088 | my @writable = sort {$a<=>$b} (keys %{$self->{deferred}}); | |
1089 | ||
1090 | while (@writable) { | |
1091 | # gather all consecutive records from the front of @writable | |
1092 | my $first_rec = shift @writable; | |
1093 | my $last_rec = $first_rec+1; | |
1094 | ++$last_rec, shift @writable while @writable && $last_rec == $writable[0]; | |
1095 | --$last_rec; | |
1096 | $self->_fill_offsets_to($last_rec); | |
1097 | $self->_extend_file_to($last_rec); | |
1098 | $self->_splice($first_rec, $last_rec-$first_rec+1, | |
1099 | @{$self->{deferred}}{$first_rec .. $last_rec}); | |
1100 | } | |
1101 | ||
1102 | $self->_discard; # clear out defered-write-cache | |
1103 | } | |
1104 | ||
1105 | sub _flush { | |
1106 | my $self = shift; | |
1107 | my @writable = sort {$a<=>$b} (keys %{$self->{deferred}}); | |
1108 | my @args; | |
1109 | my @adjust; | |
1110 | ||
1111 | while (@writable) { | |
1112 | # gather all consecutive records from the front of @writable | |
1113 | my $first_rec = shift @writable; | |
1114 | my $last_rec = $first_rec+1; | |
1115 | ++$last_rec, shift @writable while @writable && $last_rec == $writable[0]; | |
1116 | --$last_rec; | |
1117 | my $end = $self->_fill_offsets_to($last_rec+1); | |
1118 | if (not defined $end) { | |
1119 | $self->_extend_file_to($last_rec); | |
1120 | $end = $self->{offsets}[$last_rec]; | |
1121 | } | |
1122 | my ($start) = $self->{offsets}[$first_rec]; | |
1123 | push @args, | |
1124 | join("", @{$self->{deferred}}{$first_rec .. $last_rec}), # data | |
1125 | $start, # position | |
1126 | $end-$start; # length | |
1127 | push @adjust, [$first_rec, # starting at this position... | |
1128 | $last_rec-$first_rec+1, # this many records... | |
1129 | # are replaced with these... | |
1130 | @{$self->{deferred}}{$first_rec .. $last_rec}, | |
1131 | ]; | |
1132 | } | |
1133 | ||
1134 | $self->_mtwrite(@args); # write multiple record groups | |
1135 | $self->_discard; # clear out defered-write-cache | |
1136 | $self->_oadjust(@adjust); | |
1137 | } | |
1138 | ||
1139 | # Discard deferred writes and disable future deferred writes | |
1140 | sub discard { | |
1141 | my $self = shift; | |
1142 | $self->_discard; | |
1143 | $self->{defer} = 0; | |
1144 | } | |
1145 | ||
1146 | # Discard deferred writes, but retain old deferred writing mode | |
1147 | sub _discard { | |
1148 | my $self = shift; | |
1149 | %{$self->{deferred}} = (); | |
1150 | $self->{deferred_s} = 0; | |
1151 | $self->{deferred_max} = -1; | |
1152 | $self->{cache}->set_limit($self->{memory}); | |
1153 | } | |
1154 | ||
1155 | # Deferred writing is enabled, either explicitly ($self->{defer}) | |
1156 | # or automatically ($self->{autodeferring}) | |
1157 | sub _is_deferring { | |
1158 | my $self = shift; | |
1159 | $self->{defer} || $self->{autodeferring}; | |
1160 | } | |
1161 | ||
1162 | # The largest record number of any deferred record | |
1163 | sub _defer_max { | |
1164 | my $self = shift; | |
1165 | return $self->{deferred_max} if defined $self->{deferred_max}; | |
1166 | my $max = -1; | |
1167 | for my $key (keys %{$self->{deferred}}) { | |
1168 | $max = $key if $key > $max; | |
1169 | } | |
1170 | $self->{deferred_max} = $max; | |
1171 | $max; | |
1172 | } | |
1173 | ||
1174 | ################################################################ | |
1175 | # | |
1176 | # Matters related to autodeferment | |
1177 | # | |
1178 | ||
1179 | # Get/set autodefer option | |
1180 | sub autodefer { | |
1181 | my $self = shift; | |
1182 | if (@_) { | |
1183 | my $old = $self->{autodefer}; | |
1184 | $self->{autodefer} = shift; | |
1185 | if ($old) { | |
1186 | $self->_stop_autodeferring; | |
1187 | @{$self->{ad_history}} = (); | |
1188 | } | |
1189 | $old; | |
1190 | } else { | |
1191 | $self->{autodefer}; | |
1192 | } | |
1193 | } | |
1194 | ||
1195 | # The user is trying to store record #$n Record that in the history, | |
1196 | # and then enable (or disable) autodeferment if that seems useful. | |
1197 | # Note that it's OK for $n to be a non-number, as long as the function | |
1198 | # is prepared to deal with that. Nobody else looks at the ad_history. | |
1199 | # | |
1200 | # Now, what does the ad_history mean, and what is this function doing? | |
1201 | # Essentially, the idea is to enable autodeferring when we see that the | |
1202 | # user has made three consecutive STORE calls to three consecutive records. | |
1203 | # ("Three" is actually ->{autodefer_threshhold}.) | |
1204 | # A STORE call for record #$n inserts $n into the autodefer history, | |
1205 | # and if the history contains three consecutive records, we enable | |
1206 | # autodeferment. An ad_history of [X, Y] means that the most recent | |
1207 | # STOREs were for records X, X+1, ..., Y, in that order. | |
1208 | # | |
1209 | # Inserting a nonconsecutive number erases the history and starts over. | |
1210 | # | |
1211 | # Performing a special operation like SPLICE erases the history. | |
1212 | # | |
1213 | # There's one special case: CLEAR means that CLEAR was just called. | |
1214 | # In this case, we prime the history with [-2, -1] so that if the next | |
1215 | # write is for record 0, autodeferring goes on immediately. This is for | |
1216 | # the common special case of "@a = (...)". | |
1217 | # | |
1218 | sub _annotate_ad_history { | |
1219 | my ($self, $n) = @_; | |
1220 | return unless $self->{autodefer}; # feature is disabled | |
1221 | return if $self->{defer}; # already in explicit defer mode | |
1222 | return unless $self->{offsets}[-1] >= $self->{autodefer_filelen_threshhold}; | |
1223 | ||
1224 | local *H = $self->{ad_history}; | |
1225 | if ($n eq 'CLEAR') { | |
1226 | @H = (-2, -1); # prime the history with fake records | |
1227 | $self->_stop_autodeferring; | |
1228 | } elsif ($n =~ /^\d+$/) { | |
1229 | if (@H == 0) { | |
1230 | @H = ($n, $n); | |
1231 | } else { # @H == 2 | |
1232 | if ($H[1] == $n-1) { # another consecutive record | |
1233 | $H[1]++; | |
1234 | if ($H[1] - $H[0] + 1 >= $self->{autodefer_threshhold}) { | |
1235 | $self->{autodeferring} = 1; | |
1236 | } | |
1237 | } else { # nonconsecutive- erase and start over | |
1238 | @H = ($n, $n); | |
1239 | $self->_stop_autodeferring; | |
1240 | } | |
1241 | } | |
1242 | } else { # SPLICE or STORESIZE or some such | |
1243 | @H = (); | |
1244 | $self->_stop_autodeferring; | |
1245 | } | |
1246 | } | |
1247 | ||
1248 | # If autodeferring was enabled, cut it out and discard the history | |
1249 | sub _stop_autodeferring { | |
1250 | my $self = shift; | |
1251 | if ($self->{autodeferring}) { | |
1252 | $self->_flush; | |
1253 | } | |
1254 | $self->{autodeferring} = 0; | |
1255 | } | |
1256 | ||
1257 | ################################################################ | |
1258 | ||
1259 | ||
1260 | # This is NOT a method. It is here for two reasons: | |
1261 | # 1. To factor a fairly complicated block out of the constructor | |
1262 | # 2. To provide access for the test suite, which need to be sure | |
1263 | # files are being written properly. | |
1264 | sub _default_recsep { | |
1265 | my $recsep = $/; | |
1266 | if ($^O eq 'MSWin32') { # Dos too? | |
1267 | # Windows users expect files to be terminated with \r\n | |
1268 | # But $/ is set to \n instead | |
1269 | # Note that this also transforms \n\n into \r\n\r\n. | |
1270 | # That is a feature. | |
1271 | $recsep =~ s/\n/\r\n/g; | |
1272 | } | |
1273 | $recsep; | |
1274 | } | |
1275 | ||
1276 | # Utility function for _check_integrity | |
1277 | sub _ci_warn { | |
1278 | my $msg = shift; | |
1279 | $msg =~ s/\n/\\n/g; | |
1280 | $msg =~ s/\r/\\r/g; | |
1281 | print "# $msg\n"; | |
1282 | } | |
1283 | ||
1284 | # Given a file, make sure the cache is consistent with the | |
1285 | # file contents and the internal data structures are consistent with | |
1286 | # each other. Returns true if everything checks out, false if not | |
1287 | # | |
1288 | # The $file argument is no longer used. It is retained for compatibility | |
1289 | # with the existing test suite. | |
1290 | sub _check_integrity { | |
1291 | my ($self, $file, $warn) = @_; | |
1292 | my $rsl = $self->{recseplen}; | |
1293 | my $rs = $self->{recsep}; | |
1294 | my $good = 1; | |
1295 | local *_; # local $_ does not work here | |
1296 | local $DIAGNOSTIC = 1; | |
1297 | ||
1298 | if (not defined $rs) { | |
1299 | _ci_warn("recsep is undef!"); | |
1300 | $good = 0; | |
1301 | } elsif ($rs eq "") { | |
1302 | _ci_warn("recsep is empty!"); | |
1303 | $good = 0; | |
1304 | } elsif ($rsl != length $rs) { | |
1305 | my $ln = length $rs; | |
1306 | _ci_warn("recsep <$rs> has length $ln, should be $rsl"); | |
1307 | $good = 0; | |
1308 | } | |
1309 | ||
1310 | if (not defined $self->{offsets}[0]) { | |
1311 | _ci_warn("offset 0 is missing!"); | |
1312 | $good = 0; | |
1313 | ||
1314 | } elsif ($self->{offsets}[0] != 0) { | |
1315 | _ci_warn("rec 0: offset <$self->{offsets}[0]> s/b 0!"); | |
1316 | $good = 0; | |
1317 | } | |
1318 | ||
1319 | my $cached = 0; | |
1320 | { | |
1321 | local *F = $self->{fh}; | |
1322 | seek F, 0, SEEK_SET; | |
1323 | local $. = 0; | |
1324 | local $/ = $rs; | |
1325 | ||
1326 | while (<F>) { | |
1327 | my $n = $. - 1; | |
1328 | my $cached = $self->{cache}->_produce($n); | |
1329 | my $offset = $self->{offsets}[$.]; | |
1330 | my $ao = tell F; | |
1331 | if (defined $offset && $offset != $ao) { | |
1332 | _ci_warn("rec $n: offset <$offset> actual <$ao>"); | |
1333 | $good = 0; | |
1334 | } | |
1335 | if (defined $cached && $_ ne $cached && ! $self->{deferred}{$n}) { | |
1336 | $good = 0; | |
1337 | _ci_warn("rec $n: cached <$cached> actual <$_>"); | |
1338 | } | |
1339 | if (defined $cached && substr($cached, -$rsl) ne $rs) { | |
1340 | $good = 0; | |
1341 | _ci_warn("rec $n in the cache is missing the record separator"); | |
1342 | } | |
1343 | if (! defined $offset && $self->{eof}) { | |
1344 | $good = 0; | |
1345 | _ci_warn("The offset table was marked complete, but it is missing element $."); | |
1346 | } | |
1347 | } | |
1348 | if (@{$self->{offsets}} > $.+1) { | |
1349 | $good = 0; | |
1350 | my $n = @{$self->{offsets}}; | |
1351 | _ci_warn("The offset table has $n items, but the file has only $."); | |
1352 | } | |
1353 | ||
1354 | my $deferring = $self->_is_deferring; | |
1355 | for my $n ($self->{cache}->ckeys) { | |
1356 | my $r = $self->{cache}->_produce($n); | |
1357 | $cached += length($r); | |
1358 | next if $n+1 <= $.; # checked this already | |
1359 | _ci_warn("spurious caching of record $n"); | |
1360 | $good = 0; | |
1361 | } | |
1362 | my $b = $self->{cache}->bytes; | |
1363 | if ($cached != $b) { | |
1364 | _ci_warn("cache size is $b, should be $cached"); | |
1365 | $good = 0; | |
1366 | } | |
1367 | } | |
1368 | ||
1369 | # That cache has its own set of tests | |
1370 | $good = 0 unless $self->{cache}->_check_integrity; | |
1371 | ||
1372 | # Now let's check the deferbuffer | |
1373 | # Unless deferred writing is enabled, it should be empty | |
1374 | if (! $self->_is_deferring && %{$self->{deferred}}) { | |
1375 | _ci_warn("deferred writing disabled, but deferbuffer nonempty"); | |
1376 | $good = 0; | |
1377 | } | |
1378 | ||
1379 | # Any record in the deferbuffer should *not* be present in the readcache | |
1380 | my $deferred_s = 0; | |
1381 | while (my ($n, $r) = each %{$self->{deferred}}) { | |
1382 | $deferred_s += length($r); | |
1383 | if (defined $self->{cache}->_produce($n)) { | |
1384 | _ci_warn("record $n is in the deferbuffer *and* the readcache"); | |
1385 | $good = 0; | |
1386 | } | |
1387 | if (substr($r, -$rsl) ne $rs) { | |
1388 | _ci_warn("rec $n in the deferbuffer is missing the record separator"); | |
1389 | $good = 0; | |
1390 | } | |
1391 | } | |
1392 | ||
1393 | # Total size of deferbuffer should match internal total | |
1394 | if ($deferred_s != $self->{deferred_s}) { | |
1395 | _ci_warn("buffer size is $self->{deferred_s}, should be $deferred_s"); | |
1396 | $good = 0; | |
1397 | } | |
1398 | ||
1399 | # Total size of deferbuffer should not exceed the specified limit | |
1400 | if ($deferred_s > $self->{dw_size}) { | |
1401 | _ci_warn("buffer size is $self->{deferred_s} which exceeds the limit of $self->{dw_size}"); | |
1402 | $good = 0; | |
1403 | } | |
1404 | ||
1405 | # Total size of cached data should not exceed the specified limit | |
1406 | if ($deferred_s + $cached > $self->{memory}) { | |
1407 | my $total = $deferred_s + $cached; | |
1408 | _ci_warn("total stored data size is $total which exceeds the limit of $self->{memory}"); | |
1409 | $good = 0; | |
1410 | } | |
1411 | ||
1412 | # Stuff related to autodeferment | |
1413 | if (!$self->{autodefer} && @{$self->{ad_history}}) { | |
1414 | _ci_warn("autodefer is disabled, but ad_history is nonempty"); | |
1415 | $good = 0; | |
1416 | } | |
1417 | if ($self->{autodeferring} && $self->{defer}) { | |
1418 | _ci_warn("both autodeferring and explicit deferring are active"); | |
1419 | $good = 0; | |
1420 | } | |
1421 | if (@{$self->{ad_history}} == 0) { | |
1422 | # That's OK, no additional tests required | |
1423 | } elsif (@{$self->{ad_history}} == 2) { | |
1424 | my @non_number = grep !/^-?\d+$/, @{$self->{ad_history}}; | |
1425 | if (@non_number) { | |
1426 | my $msg; | |
1427 | { local $" = ')('; | |
1428 | $msg = "ad_history contains non-numbers (@{$self->{ad_history}})"; | |
1429 | } | |
1430 | _ci_warn($msg); | |
1431 | $good = 0; | |
1432 | } elsif ($self->{ad_history}[1] < $self->{ad_history}[0]) { | |
1433 | _ci_warn("ad_history has nonsensical values @{$self->{ad_history}}"); | |
1434 | $good = 0; | |
1435 | } | |
1436 | } else { | |
1437 | _ci_warn("ad_history has bad length <@{$self->{ad_history}}>"); | |
1438 | $good = 0; | |
1439 | } | |
1440 | ||
1441 | $good; | |
1442 | } | |
1443 | ||
1444 | ################################################################ | |
1445 | # | |
1446 | # Tie::File::Cache | |
1447 | # | |
1448 | # Read cache | |
1449 | ||
1450 | package Tie::File::Cache; | |
1451 | $Tie::File::Cache::VERSION = $Tie::File::VERSION; | |
1452 | use Carp ':DEFAULT', 'confess'; | |
1453 | ||
1454 | sub HEAP () { 0 } | |
1455 | sub HASH () { 1 } | |
1456 | sub MAX () { 2 } | |
1457 | sub BYTES() { 3 } | |
1458 | #sub STAT () { 4 } # Array with request statistics for each record | |
1459 | #sub MISS () { 5 } # Total number of cache misses | |
1460 | #sub REQ () { 6 } # Total number of cache requests | |
1461 | use strict 'vars'; | |
1462 | ||
1463 | sub new { | |
1464 | my ($pack, $max) = @_; | |
1465 | local *_; | |
1466 | croak "missing argument to ->new" unless defined $max; | |
1467 | my $self = []; | |
1468 | bless $self => $pack; | |
1469 | @$self = (Tie::File::Heap->new($self), {}, $max, 0); | |
1470 | $self; | |
1471 | } | |
1472 | ||
1473 | sub adj_limit { | |
1474 | my ($self, $n) = @_; | |
1475 | $self->[MAX] += $n; | |
1476 | } | |
1477 | ||
1478 | sub set_limit { | |
1479 | my ($self, $n) = @_; | |
1480 | $self->[MAX] = $n; | |
1481 | } | |
1482 | ||
1483 | # For internal use only | |
1484 | # Will be called by the heap structure to notify us that a certain | |
1485 | # piece of data has moved from one heap element to another. | |
1486 | # $k is the hash key of the item | |
1487 | # $n is the new index into the heap at which it is stored | |
1488 | # If $n is undefined, the item has been removed from the heap. | |
1489 | sub _heap_move { | |
1490 | my ($self, $k, $n) = @_; | |
1491 | if (defined $n) { | |
1492 | $self->[HASH]{$k} = $n; | |
1493 | } else { | |
1494 | delete $self->[HASH]{$k}; | |
1495 | } | |
1496 | } | |
1497 | ||
1498 | sub insert { | |
1499 | my ($self, $key, $val) = @_; | |
1500 | local *_; | |
1501 | croak "missing argument to ->insert" unless defined $key; | |
1502 | unless (defined $self->[MAX]) { | |
1503 | confess "undefined max" ; | |
1504 | } | |
1505 | confess "undefined val" unless defined $val; | |
1506 | return if length($val) > $self->[MAX]; | |
1507 | ||
1508 | # if ($self->[STAT]) { | |
1509 | # $self->[STAT][$key] = 1; | |
1510 | # return; | |
1511 | # } | |
1512 | ||
1513 | my $oldnode = $self->[HASH]{$key}; | |
1514 | if (defined $oldnode) { | |
1515 | my $oldval = $self->[HEAP]->set_val($oldnode, $val); | |
1516 | $self->[BYTES] -= length($oldval); | |
1517 | } else { | |
1518 | $self->[HEAP]->insert($key, $val); | |
1519 | } | |
1520 | $self->[BYTES] += length($val); | |
1521 | $self->flush if $self->[BYTES] > $self->[MAX]; | |
1522 | } | |
1523 | ||
1524 | sub expire { | |
1525 | my $self = shift; | |
1526 | my $old_data = $self->[HEAP]->popheap; | |
1527 | return unless defined $old_data; | |
1528 | $self->[BYTES] -= length $old_data; | |
1529 | $old_data; | |
1530 | } | |
1531 | ||
1532 | sub remove { | |
1533 | my ($self, @keys) = @_; | |
1534 | my @result; | |
1535 | ||
1536 | # if ($self->[STAT]) { | |
1537 | # for my $key (@keys) { | |
1538 | # $self->[STAT][$key] = 0; | |
1539 | # } | |
1540 | # return; | |
1541 | # } | |
1542 | ||
1543 | for my $key (@keys) { | |
1544 | next unless exists $self->[HASH]{$key}; | |
1545 | my $old_data = $self->[HEAP]->remove($self->[HASH]{$key}); | |
1546 | $self->[BYTES] -= length $old_data; | |
1547 | push @result, $old_data; | |
1548 | } | |
1549 | @result; | |
1550 | } | |
1551 | ||
1552 | sub lookup { | |
1553 | my ($self, $key) = @_; | |
1554 | local *_; | |
1555 | croak "missing argument to ->lookup" unless defined $key; | |
1556 | ||
1557 | # if ($self->[STAT]) { | |
1558 | # $self->[MISS]++ if $self->[STAT][$key]++ == 0; | |
1559 | # $self->[REQ]++; | |
1560 | # my $hit_rate = 1 - $self->[MISS] / $self->[REQ]; | |
1561 | # # Do some testing to determine this threshhold | |
1562 | # $#$self = STAT - 1 if $hit_rate > 0.20; | |
1563 | # } | |
1564 | ||
1565 | if (exists $self->[HASH]{$key}) { | |
1566 | $self->[HEAP]->lookup($self->[HASH]{$key}); | |
1567 | } else { | |
1568 | return; | |
1569 | } | |
1570 | } | |
1571 | ||
1572 | # For internal use only | |
1573 | sub _produce { | |
1574 | my ($self, $key) = @_; | |
1575 | my $loc = $self->[HASH]{$key}; | |
1576 | return unless defined $loc; | |
1577 | $self->[HEAP][$loc][2]; | |
1578 | } | |
1579 | ||
1580 | # For internal use only | |
1581 | sub _promote { | |
1582 | my ($self, $key) = @_; | |
1583 | $self->[HEAP]->promote($self->[HASH]{$key}); | |
1584 | } | |
1585 | ||
1586 | sub empty { | |
1587 | my ($self) = @_; | |
1588 | %{$self->[HASH]} = (); | |
1589 | $self->[BYTES] = 0; | |
1590 | $self->[HEAP]->empty; | |
1591 | # @{$self->[STAT]} = (); | |
1592 | # $self->[MISS] = 0; | |
1593 | # $self->[REQ] = 0; | |
1594 | } | |
1595 | ||
1596 | sub is_empty { | |
1597 | my ($self) = @_; | |
1598 | keys %{$self->[HASH]} == 0; | |
1599 | } | |
1600 | ||
1601 | sub update { | |
1602 | my ($self, $key, $val) = @_; | |
1603 | local *_; | |
1604 | croak "missing argument to ->update" unless defined $key; | |
1605 | if (length($val) > $self->[MAX]) { | |
1606 | my ($oldval) = $self->remove($key); | |
1607 | $self->[BYTES] -= length($oldval) if defined $oldval; | |
1608 | } elsif (exists $self->[HASH]{$key}) { | |
1609 | my $oldval = $self->[HEAP]->set_val($self->[HASH]{$key}, $val); | |
1610 | $self->[BYTES] += length($val); | |
1611 | $self->[BYTES] -= length($oldval) if defined $oldval; | |
1612 | } else { | |
1613 | $self->[HEAP]->insert($key, $val); | |
1614 | $self->[BYTES] += length($val); | |
1615 | } | |
1616 | $self->flush; | |
1617 | } | |
1618 | ||
1619 | sub rekey { | |
1620 | my ($self, $okeys, $nkeys) = @_; | |
1621 | local *_; | |
1622 | my %map; | |
1623 | @map{@$okeys} = @$nkeys; | |
1624 | croak "missing argument to ->rekey" unless defined $nkeys; | |
1625 | croak "length mismatch in ->rekey arguments" unless @$nkeys == @$okeys; | |
1626 | my %adjusted; # map new keys to heap indices | |
1627 | # You should be able to cut this to one loop TODO XXX | |
1628 | for (0 .. $#$okeys) { | |
1629 | $adjusted{$nkeys->[$_]} = delete $self->[HASH]{$okeys->[$_]}; | |
1630 | } | |
1631 | while (my ($nk, $ix) = each %adjusted) { | |
1632 | # @{$self->[HASH]}{keys %adjusted} = values %adjusted; | |
1633 | $self->[HEAP]->rekey($ix, $nk); | |
1634 | $self->[HASH]{$nk} = $ix; | |
1635 | } | |
1636 | } | |
1637 | ||
1638 | sub ckeys { | |
1639 | my $self = shift; | |
1640 | my @a = keys %{$self->[HASH]}; | |
1641 | @a; | |
1642 | } | |
1643 | ||
1644 | # Return total amount of cached data | |
1645 | sub bytes { | |
1646 | my $self = shift; | |
1647 | $self->[BYTES]; | |
1648 | } | |
1649 | ||
1650 | # Expire oldest item from cache until cache size is smaller than $max | |
1651 | sub reduce_size_to { | |
1652 | my ($self, $max) = @_; | |
1653 | until ($self->[BYTES] <= $max) { | |
1654 | # Note that Tie::File::Cache::expire has been inlined here | |
1655 | my $old_data = $self->[HEAP]->popheap; | |
1656 | return unless defined $old_data; | |
1657 | $self->[BYTES] -= length $old_data; | |
1658 | } | |
1659 | } | |
1660 | ||
1661 | # Why not just $self->reduce_size_to($self->[MAX])? | |
1662 | # Try this when things stabilize TODO XXX | |
1663 | # If the cache is too full, expire the oldest records | |
1664 | sub flush { | |
1665 | my $self = shift; | |
1666 | $self->reduce_size_to($self->[MAX]) if $self->[BYTES] > $self->[MAX]; | |
1667 | } | |
1668 | ||
1669 | # For internal use only | |
1670 | sub _produce_lru { | |
1671 | my $self = shift; | |
1672 | $self->[HEAP]->expire_order; | |
1673 | } | |
1674 | ||
1675 | BEGIN { *_ci_warn = \&Tie::File::_ci_warn } | |
1676 | ||
1677 | sub _check_integrity { # For CACHE | |
1678 | my $self = shift; | |
1679 | my $good = 1; | |
1680 | ||
1681 | # Test HEAP | |
1682 | $self->[HEAP]->_check_integrity or $good = 0; | |
1683 | ||
1684 | # Test HASH | |
1685 | my $bytes = 0; | |
1686 | for my $k (keys %{$self->[HASH]}) { | |
1687 | if ($k ne '0' && $k !~ /^[1-9][0-9]*$/) { | |
1688 | $good = 0; | |
1689 | _ci_warn "Cache hash key <$k> is non-numeric"; | |
1690 | } | |
1691 | ||
1692 | my $h = $self->[HASH]{$k}; | |
1693 | if (! defined $h) { | |
1694 | $good = 0; | |
1695 | _ci_warn "Heap index number for key $k is undefined"; | |
1696 | } elsif ($h == 0) { | |
1697 | $good = 0; | |
1698 | _ci_warn "Heap index number for key $k is zero"; | |
1699 | } else { | |
1700 | my $j = $self->[HEAP][$h]; | |
1701 | if (! defined $j) { | |
1702 | $good = 0; | |
1703 | _ci_warn "Heap contents key $k (=> $h) are undefined"; | |
1704 | } else { | |
1705 | $bytes += length($j->[2]); | |
1706 | if ($k ne $j->[1]) { | |
1707 | $good = 0; | |
1708 | _ci_warn "Heap contents key $k (=> $h) is $j->[1], should be $k"; | |
1709 | } | |
1710 | } | |
1711 | } | |
1712 | } | |
1713 | ||
1714 | # Test BYTES | |
1715 | if ($bytes != $self->[BYTES]) { | |
1716 | $good = 0; | |
1717 | _ci_warn "Total data in cache is $bytes, expected $self->[BYTES]"; | |
1718 | } | |
1719 | ||
1720 | # Test MAX | |
1721 | if ($bytes > $self->[MAX]) { | |
1722 | $good = 0; | |
1723 | _ci_warn "Total data in cache is $bytes, exceeds maximum $self->[MAX]"; | |
1724 | } | |
1725 | ||
1726 | return $good; | |
1727 | } | |
1728 | ||
1729 | sub delink { | |
1730 | my $self = shift; | |
1731 | $self->[HEAP] = undef; # Bye bye heap | |
1732 | } | |
1733 | ||
1734 | ################################################################ | |
1735 | # | |
1736 | # Tie::File::Heap | |
1737 | # | |
1738 | # Heap data structure for use by cache LRU routines | |
1739 | ||
1740 | package Tie::File::Heap; | |
1741 | use Carp ':DEFAULT', 'confess'; | |
1742 | $Tie::File::Heap::VERSION = $Tie::File::Cache::VERSION; | |
1743 | sub SEQ () { 0 }; | |
1744 | sub KEY () { 1 }; | |
1745 | sub DAT () { 2 }; | |
1746 | ||
1747 | sub new { | |
1748 | my ($pack, $cache) = @_; | |
1749 | die "$pack: Parent cache object $cache does not support _heap_move method" | |
1750 | unless eval { $cache->can('_heap_move') }; | |
1751 | my $self = [[0,$cache,0]]; | |
1752 | bless $self => $pack; | |
1753 | } | |
1754 | ||
1755 | # Allocate a new sequence number, larger than all previously allocated numbers | |
1756 | sub _nseq { | |
1757 | my $self = shift; | |
1758 | $self->[0][0]++; | |
1759 | } | |
1760 | ||
1761 | sub _cache { | |
1762 | my $self = shift; | |
1763 | $self->[0][1]; | |
1764 | } | |
1765 | ||
1766 | sub _nelts { | |
1767 | my $self = shift; | |
1768 | $self->[0][2]; | |
1769 | } | |
1770 | ||
1771 | sub _nelts_inc { | |
1772 | my $self = shift; | |
1773 | ++$self->[0][2]; | |
1774 | } | |
1775 | ||
1776 | sub _nelts_dec { | |
1777 | my $self = shift; | |
1778 | --$self->[0][2]; | |
1779 | } | |
1780 | ||
1781 | sub is_empty { | |
1782 | my $self = shift; | |
1783 | $self->_nelts == 0; | |
1784 | } | |
1785 | ||
1786 | sub empty { | |
1787 | my $self = shift; | |
1788 | $#$self = 0; | |
1789 | $self->[0][2] = 0; | |
1790 | $self->[0][0] = 0; # might as well reset the sequence numbers | |
1791 | } | |
1792 | ||
1793 | # notify the parent cache object that we moved something | |
1794 | sub _heap_move { | |
1795 | my $self = shift; | |
1796 | $self->_cache->_heap_move(@_); | |
1797 | } | |
1798 | ||
1799 | # Insert a piece of data into the heap with the indicated sequence number. | |
1800 | # The item with the smallest sequence number is always at the top. | |
1801 | # If no sequence number is specified, allocate a new one and insert the | |
1802 | # item at the bottom. | |
1803 | sub insert { | |
1804 | my ($self, $key, $data, $seq) = @_; | |
1805 | $seq = $self->_nseq unless defined $seq; | |
1806 | $self->_insert_new([$seq, $key, $data]); | |
1807 | } | |
1808 | ||
1809 | # Insert a new, fresh item at the bottom of the heap | |
1810 | sub _insert_new { | |
1811 | my ($self, $item) = @_; | |
1812 | my $i = @$self; | |
1813 | $i = int($i/2) until defined $self->[$i/2]; | |
1814 | $self->[$i] = $item; | |
1815 | $self->[0][1]->_heap_move($self->[$i][KEY], $i); | |
1816 | $self->_nelts_inc; | |
1817 | } | |
1818 | ||
1819 | # Insert [$data, $seq] pair at or below item $i in the heap. | |
1820 | # If $i is omitted, default to 1 (the top element.) | |
1821 | sub _insert { | |
1822 | my ($self, $item, $i) = @_; | |
1823 | # $self->_check_loc($i) if defined $i; | |
1824 | $i = 1 unless defined $i; | |
1825 | until (! defined $self->[$i]) { | |
1826 | if ($self->[$i][SEQ] > $item->[SEQ]) { # inserted item is older | |
1827 | ($self->[$i], $item) = ($item, $self->[$i]); | |
1828 | $self->[0][1]->_heap_move($self->[$i][KEY], $i); | |
1829 | } | |
1830 | # If either is undefined, go that way. Otherwise, choose at random | |
1831 | my $dir; | |
1832 | $dir = 0 if !defined $self->[2*$i]; | |
1833 | $dir = 1 if !defined $self->[2*$i+1]; | |
1834 | $dir = int(rand(2)) unless defined $dir; | |
1835 | $i = 2*$i + $dir; | |
1836 | } | |
1837 | $self->[$i] = $item; | |
1838 | $self->[0][1]->_heap_move($self->[$i][KEY], $i); | |
1839 | $self->_nelts_inc; | |
1840 | } | |
1841 | ||
1842 | # Remove the item at node $i from the heap, moving child items upwards. | |
1843 | # The item with the smallest sequence number is always at the top. | |
1844 | # Moving items upwards maintains this condition. | |
1845 | # Return the removed item. Return undef if there was no item at node $i. | |
1846 | sub remove { | |
1847 | my ($self, $i) = @_; | |
1848 | $i = 1 unless defined $i; | |
1849 | my $top = $self->[$i]; | |
1850 | return unless defined $top; | |
1851 | while (1) { | |
1852 | my $ii; | |
1853 | my ($L, $R) = (2*$i, 2*$i+1); | |
1854 | ||
1855 | # If either is undefined, go the other way. | |
1856 | # Otherwise, go towards the smallest. | |
1857 | last unless defined $self->[$L] || defined $self->[$R]; | |
1858 | $ii = $R if not defined $self->[$L]; | |
1859 | $ii = $L if not defined $self->[$R]; | |
1860 | unless (defined $ii) { | |
1861 | $ii = $self->[$L][SEQ] < $self->[$R][SEQ] ? $L : $R; | |
1862 | } | |
1863 | ||
1864 | $self->[$i] = $self->[$ii]; # Promote child to fill vacated spot | |
1865 | $self->[0][1]->_heap_move($self->[$i][KEY], $i); | |
1866 | $i = $ii; # Fill new vacated spot | |
1867 | } | |
1868 | $self->[0][1]->_heap_move($top->[KEY], undef); | |
1869 | undef $self->[$i]; | |
1870 | $self->_nelts_dec; | |
1871 | return $top->[DAT]; | |
1872 | } | |
1873 | ||
1874 | sub popheap { | |
1875 | my $self = shift; | |
1876 | $self->remove(1); | |
1877 | } | |
1878 | ||
1879 | # set the sequence number of the indicated item to a higher number | |
1880 | # than any other item in the heap, and bubble the item down to the | |
1881 | # bottom. | |
1882 | sub promote { | |
1883 | my ($self, $n) = @_; | |
1884 | # $self->_check_loc($n); | |
1885 | $self->[$n][SEQ] = $self->_nseq; | |
1886 | my $i = $n; | |
1887 | while (1) { | |
1888 | my ($L, $R) = (2*$i, 2*$i+1); | |
1889 | my $dir; | |
1890 | last unless defined $self->[$L] || defined $self->[$R]; | |
1891 | $dir = $R unless defined $self->[$L]; | |
1892 | $dir = $L unless defined $self->[$R]; | |
1893 | unless (defined $dir) { | |
1894 | $dir = $self->[$L][SEQ] < $self->[$R][SEQ] ? $L : $R; | |
1895 | } | |
1896 | @{$self}[$i, $dir] = @{$self}[$dir, $i]; | |
1897 | for ($i, $dir) { | |
1898 | $self->[0][1]->_heap_move($self->[$_][KEY], $_) if defined $self->[$_]; | |
1899 | } | |
1900 | $i = $dir; | |
1901 | } | |
1902 | } | |
1903 | ||
1904 | # Return item $n from the heap, promoting its LRU status | |
1905 | sub lookup { | |
1906 | my ($self, $n) = @_; | |
1907 | # $self->_check_loc($n); | |
1908 | my $val = $self->[$n]; | |
1909 | $self->promote($n); | |
1910 | $val->[DAT]; | |
1911 | } | |
1912 | ||
1913 | ||
1914 | # Assign a new value for node $n, promoting it to the bottom of the heap | |
1915 | sub set_val { | |
1916 | my ($self, $n, $val) = @_; | |
1917 | # $self->_check_loc($n); | |
1918 | my $oval = $self->[$n][DAT]; | |
1919 | $self->[$n][DAT] = $val; | |
1920 | $self->promote($n); | |
1921 | return $oval; | |
1922 | } | |
1923 | ||
1924 | # The hask key has changed for an item; | |
1925 | # alter the heap's record of the hash key | |
1926 | sub rekey { | |
1927 | my ($self, $n, $new_key) = @_; | |
1928 | # $self->_check_loc($n); | |
1929 | $self->[$n][KEY] = $new_key; | |
1930 | } | |
1931 | ||
1932 | sub _check_loc { | |
1933 | my ($self, $n) = @_; | |
1934 | unless (1 || defined $self->[$n]) { | |
1935 | confess "_check_loc($n) failed"; | |
1936 | } | |
1937 | } | |
1938 | ||
1939 | BEGIN { *_ci_warn = \&Tie::File::_ci_warn } | |
1940 | ||
1941 | sub _check_integrity { | |
1942 | my $self = shift; | |
1943 | my $good = 1; | |
1944 | my %seq; | |
1945 | ||
1946 | unless (eval {$self->[0][1]->isa("Tie::File::Cache")}) { | |
1947 | _ci_warn "Element 0 of heap corrupt"; | |
1948 | $good = 0; | |
1949 | } | |
1950 | $good = 0 unless $self->_satisfies_heap_condition(1); | |
1951 | for my $i (2 .. $#{$self}) { | |
1952 | my $p = int($i/2); # index of parent node | |
1953 | if (defined $self->[$i] && ! defined $self->[$p]) { | |
1954 | _ci_warn "Element $i of heap defined, but parent $p isn't"; | |
1955 | $good = 0; | |
1956 | } | |
1957 | ||
1958 | if (defined $self->[$i]) { | |
1959 | if ($seq{$self->[$i][SEQ]}) { | |
1960 | my $seq = $self->[$i][SEQ]; | |
1961 | _ci_warn "Nodes $i and $seq{$seq} both have SEQ=$seq"; | |
1962 | $good = 0; | |
1963 | } else { | |
1964 | $seq{$self->[$i][SEQ]} = $i; | |
1965 | } | |
1966 | } | |
1967 | } | |
1968 | ||
1969 | return $good; | |
1970 | } | |
1971 | ||
1972 | sub _satisfies_heap_condition { | |
1973 | my $self = shift; | |
1974 | my $n = shift || 1; | |
1975 | my $good = 1; | |
1976 | for (0, 1) { | |
1977 | my $c = $n*2 + $_; | |
1978 | next unless defined $self->[$c]; | |
1979 | if ($self->[$n][SEQ] >= $self->[$c]) { | |
1980 | _ci_warn "Node $n of heap does not predate node $c"; | |
1981 | $good = 0 ; | |
1982 | } | |
1983 | $good = 0 unless $self->_satisfies_heap_condition($c); | |
1984 | } | |
1985 | return $good; | |
1986 | } | |
1987 | ||
1988 | # Return a list of all the values, sorted by expiration order | |
1989 | sub expire_order { | |
1990 | my $self = shift; | |
1991 | my @nodes = sort {$a->[SEQ] <=> $b->[SEQ]} $self->_nodes; | |
1992 | map { $_->[KEY] } @nodes; | |
1993 | } | |
1994 | ||
1995 | sub _nodes { | |
1996 | my $self = shift; | |
1997 | my $i = shift || 1; | |
1998 | return unless defined $self->[$i]; | |
1999 | ($self->[$i], $self->_nodes($i*2), $self->_nodes($i*2+1)); | |
2000 | } | |
2001 | ||
2002 | "Cogito, ergo sum."; # don't forget to return a true value from the file | |
2003 | ||
2004 | __END__ | |
2005 | ||
2006 | =head1 NAME | |
2007 | ||
2008 | Tie::File - Access the lines of a disk file via a Perl array | |
2009 | ||
2010 | =head1 SYNOPSIS | |
2011 | ||
2012 | # This file documents Tie::File version 0.97 | |
2013 | use Tie::File; | |
2014 | ||
2015 | tie @array, 'Tie::File', filename or die ...; | |
2016 | ||
2017 | $array[13] = 'blah'; # line 13 of the file is now 'blah' | |
2018 | print $array[42]; # display line 42 of the file | |
2019 | ||
2020 | $n_recs = @array; # how many records are in the file? | |
2021 | $#array -= 2; # chop two records off the end | |
2022 | ||
2023 | ||
2024 | for (@array) { | |
2025 | s/PERL/Perl/g; # Replace PERL with Perl everywhere in the file | |
2026 | } | |
2027 | ||
2028 | # These are just like regular push, pop, unshift, shift, and splice | |
2029 | # Except that they modify the file in the way you would expect | |
2030 | ||
2031 | push @array, new recs...; | |
2032 | my $r1 = pop @array; | |
2033 | unshift @array, new recs...; | |
2034 | my $r2 = shift @array; | |
2035 | @old_recs = splice @array, 3, 7, new recs...; | |
2036 | ||
2037 | untie @array; # all finished | |
2038 | ||
2039 | ||
2040 | =head1 DESCRIPTION | |
2041 | ||
2042 | C<Tie::File> represents a regular text file as a Perl array. Each | |
2043 | element in the array corresponds to a record in the file. The first | |
2044 | line of the file is element 0 of the array; the second line is element | |
2045 | 1, and so on. | |
2046 | ||
2047 | The file is I<not> loaded into memory, so this will work even for | |
2048 | gigantic files. | |
2049 | ||
2050 | Changes to the array are reflected in the file immediately. | |
2051 | ||
2052 | Lazy people and beginners may now stop reading the manual. | |
2053 | ||
2054 | =head2 C<recsep> | |
2055 | ||
2056 | What is a 'record'? By default, the meaning is the same as for the | |
2057 | C<E<lt>...E<gt>> operator: It's a string terminated by C<$/>, which is | |
2058 | probably C<"\n">. (Minor exception: on DOS and Win32 systems, a | |
2059 | 'record' is a string terminated by C<"\r\n">.) You may change the | |
2060 | definition of "record" by supplying the C<recsep> option in the C<tie> | |
2061 | call: | |
2062 | ||
2063 | tie @array, 'Tie::File', $file, recsep => 'es'; | |
2064 | ||
2065 | This says that records are delimited by the string C<es>. If the file | |
2066 | contained the following data: | |
2067 | ||
2068 | Curse these pesky flies!\n | |
2069 | ||
2070 | then the C<@array> would appear to have four elements: | |
2071 | ||
2072 | "Curse th" | |
2073 | "e p" | |
2074 | "ky fli" | |
2075 | "!\n" | |
2076 | ||
2077 | An undefined value is not permitted as a record separator. Perl's | |
2078 | special "paragraph mode" semantics (E<agrave> la C<$/ = "">) are not | |
2079 | emulated. | |
2080 | ||
2081 | Records read from the tied array do not have the record separator | |
2082 | string on the end; this is to allow | |
2083 | ||
2084 | $array[17] .= "extra"; | |
2085 | ||
2086 | to work as expected. | |
2087 | ||
2088 | (See L<"autochomp">, below.) Records stored into the array will have | |
2089 | the record separator string appended before they are written to the | |
2090 | file, if they don't have one already. For example, if the record | |
2091 | separator string is C<"\n">, then the following two lines do exactly | |
2092 | the same thing: | |
2093 | ||
2094 | $array[17] = "Cherry pie"; | |
2095 | $array[17] = "Cherry pie\n"; | |
2096 | ||
2097 | The result is that the contents of line 17 of the file will be | |
2098 | replaced with "Cherry pie"; a newline character will separate line 17 | |
2099 | from line 18. This means that this code will do nothing: | |
2100 | ||
2101 | chomp $array[17]; | |
2102 | ||
2103 | Because the C<chomp>ed value will have the separator reattached when | |
2104 | it is written back to the file. There is no way to create a file | |
2105 | whose trailing record separator string is missing. | |
2106 | ||
2107 | Inserting records that I<contain> the record separator string is not | |
2108 | supported by this module. It will probably produce a reasonable | |
2109 | result, but what this result will be may change in a future version. | |
2110 | Use 'splice' to insert records or to replace one record with several. | |
2111 | ||
2112 | =head2 C<autochomp> | |
2113 | ||
2114 | Normally, array elements have the record separator removed, so that if | |
2115 | the file contains the text | |
2116 | ||
2117 | Gold | |
2118 | Frankincense | |
2119 | Myrrh | |
2120 | ||
2121 | the tied array will appear to contain C<("Gold", "Frankincense", | |
2122 | "Myrrh")>. If you set C<autochomp> to a false value, the record | |
2123 | separator will not be removed. If the file above was tied with | |
2124 | ||
2125 | tie @gifts, "Tie::File", $gifts, autochomp => 0; | |
2126 | ||
2127 | then the array C<@gifts> would appear to contain C<("Gold\n", | |
2128 | "Frankincense\n", "Myrrh\n")>, or (on Win32 systems) C<("Gold\r\n", | |
2129 | "Frankincense\r\n", "Myrrh\r\n")>. | |
2130 | ||
2131 | =head2 C<mode> | |
2132 | ||
2133 | Normally, the specified file will be opened for read and write access, | |
2134 | and will be created if it does not exist. (That is, the flags | |
2135 | C<O_RDWR | O_CREAT> are supplied in the C<open> call.) If you want to | |
2136 | change this, you may supply alternative flags in the C<mode> option. | |
2137 | See L<Fcntl> for a listing of available flags. | |
2138 | For example: | |
2139 | ||
2140 | # open the file if it exists, but fail if it does not exist | |
2141 | use Fcntl 'O_RDWR'; | |
2142 | tie @array, 'Tie::File', $file, mode => O_RDWR; | |
2143 | ||
2144 | # create the file if it does not exist | |
2145 | use Fcntl 'O_RDWR', 'O_CREAT'; | |
2146 | tie @array, 'Tie::File', $file, mode => O_RDWR | O_CREAT; | |
2147 | ||
2148 | # open an existing file in read-only mode | |
2149 | use Fcntl 'O_RDONLY'; | |
2150 | tie @array, 'Tie::File', $file, mode => O_RDONLY; | |
2151 | ||
2152 | Opening the data file in write-only or append mode is not supported. | |
2153 | ||
2154 | =head2 C<memory> | |
2155 | ||
2156 | This is an upper limit on the amount of memory that C<Tie::File> will | |
2157 | consume at any time while managing the file. This is used for two | |
2158 | things: managing the I<read cache> and managing the I<deferred write | |
2159 | buffer>. | |
2160 | ||
2161 | Records read in from the file are cached, to avoid having to re-read | |
2162 | them repeatedly. If you read the same record twice, the first time it | |
2163 | will be stored in memory, and the second time it will be fetched from | |
2164 | the I<read cache>. The amount of data in the read cache will not | |
2165 | exceed the value you specified for C<memory>. If C<Tie::File> wants | |
2166 | to cache a new record, but the read cache is full, it will make room | |
2167 | by expiring the least-recently visited records from the read cache. | |
2168 | ||
2169 | The default memory limit is 2Mib. You can adjust the maximum read | |
2170 | cache size by supplying the C<memory> option. The argument is the | |
2171 | desired cache size, in bytes. | |
2172 | ||
2173 | # I have a lot of memory, so use a large cache to speed up access | |
2174 | tie @array, 'Tie::File', $file, memory => 20_000_000; | |
2175 | ||
2176 | Setting the memory limit to 0 will inhibit caching; records will be | |
2177 | fetched from disk every time you examine them. | |
2178 | ||
2179 | The C<memory> value is not an absolute or exact limit on the memory | |
2180 | used. C<Tie::File> objects contains some structures besides the read | |
2181 | cache and the deferred write buffer, whose sizes are not charged | |
2182 | against C<memory>. | |
2183 | ||
2184 | The cache itself consumes about 310 bytes per cached record, so if | |
2185 | your file has many short records, you may want to decrease the cache | |
2186 | memory limit, or else the cache overhead may exceed the size of the | |
2187 | cached data. | |
2188 | ||
2189 | ||
2190 | =head2 C<dw_size> | |
2191 | ||
2192 | (This is an advanced feature. Skip this section on first reading.) | |
2193 | ||
2194 | If you use deferred writing (See L<"Deferred Writing">, below) then | |
2195 | data you write into the array will not be written directly to the | |
2196 | file; instead, it will be saved in the I<deferred write buffer> to be | |
2197 | written out later. Data in the deferred write buffer is also charged | |
2198 | against the memory limit you set with the C<memory> option. | |
2199 | ||
2200 | You may set the C<dw_size> option to limit the amount of data that can | |
2201 | be saved in the deferred write buffer. This limit may not exceed the | |
2202 | total memory limit. For example, if you set C<dw_size> to 1000 and | |
2203 | C<memory> to 2500, that means that no more than 1000 bytes of deferred | |
2204 | writes will be saved up. The space available for the read cache will | |
2205 | vary, but it will always be at least 1500 bytes (if the deferred write | |
2206 | buffer is full) and it could grow as large as 2500 bytes (if the | |
2207 | deferred write buffer is empty.) | |
2208 | ||
2209 | If you don't specify a C<dw_size>, it defaults to the entire memory | |
2210 | limit. | |
2211 | ||
2212 | =head2 Option Format | |
2213 | ||
2214 | C<-mode> is a synonym for C<mode>. C<-recsep> is a synonym for | |
2215 | C<recsep>. C<-memory> is a synonym for C<memory>. You get the | |
2216 | idea. | |
2217 | ||
2218 | =head1 Public Methods | |
2219 | ||
2220 | The C<tie> call returns an object, say C<$o>. You may call | |
2221 | ||
2222 | $rec = $o->FETCH($n); | |
2223 | $o->STORE($n, $rec); | |
2224 | ||
2225 | to fetch or store the record at line C<$n>, respectively; similarly | |
2226 | the other tied array methods. (See L<perltie> for details.) You may | |
2227 | also call the following methods on this object: | |
2228 | ||
2229 | =head2 C<flock> | |
2230 | ||
2231 | $o->flock(MODE) | |
2232 | ||
2233 | will lock the tied file. C<MODE> has the same meaning as the second | |
2234 | argument to the Perl built-in C<flock> function; for example | |
2235 | C<LOCK_SH> or C<LOCK_EX | LOCK_NB>. (These constants are provided by | |
2236 | the C<use Fcntl ':flock'> declaration.) | |
2237 | ||
2238 | C<MODE> is optional; the default is C<LOCK_EX>. | |
2239 | ||
2240 | C<Tie::File> maintains an internal table of the byte offset of each | |
2241 | record it has seen in the file. | |
2242 | ||
2243 | When you use C<flock> to lock the file, C<Tie::File> assumes that the | |
2244 | read cache is no longer trustworthy, because another process might | |
2245 | have modified the file since the last time it was read. Therefore, a | |
2246 | successful call to C<flock> discards the contents of the read cache | |
2247 | and the internal record offset table. | |
2248 | ||
2249 | C<Tie::File> promises that the following sequence of operations will | |
2250 | be safe: | |
2251 | ||
2252 | my $o = tie @array, "Tie::File", $filename; | |
2253 | $o->flock; | |
2254 | ||
2255 | In particular, C<Tie::File> will I<not> read or write the file during | |
2256 | the C<tie> call. (Exception: Using C<mode =E<gt> O_TRUNC> will, of | |
2257 | course, erase the file during the C<tie> call. If you want to do this | |
2258 | safely, then open the file without C<O_TRUNC>, lock the file, and use | |
2259 | C<@array = ()>.) | |
2260 | ||
2261 | The best way to unlock a file is to discard the object and untie the | |
2262 | array. It is probably unsafe to unlock the file without also untying | |
2263 | it, because if you do, changes may remain unwritten inside the object. | |
2264 | That is why there is no shortcut for unlocking. If you really want to | |
2265 | unlock the file prematurely, you know what to do; if you don't know | |
2266 | what to do, then don't do it. | |
2267 | ||
2268 | All the usual warnings about file locking apply here. In particular, | |
2269 | note that file locking in Perl is B<advisory>, which means that | |
2270 | holding a lock will not prevent anyone else from reading, writing, or | |
2271 | erasing the file; it only prevents them from getting another lock at | |
2272 | the same time. Locks are analogous to green traffic lights: If you | |
2273 | have a green light, that does not prevent the idiot coming the other | |
2274 | way from plowing into you sideways; it merely guarantees to you that | |
2275 | the idiot does not also have a green light at the same time. | |
2276 | ||
2277 | =head2 C<autochomp> | |
2278 | ||
2279 | my $old_value = $o->autochomp(0); # disable autochomp option | |
2280 | my $old_value = $o->autochomp(1); # enable autochomp option | |
2281 | ||
2282 | my $ac = $o->autochomp(); # recover current value | |
2283 | ||
2284 | See L<"autochomp">, above. | |
2285 | ||
2286 | =head2 C<defer>, C<flush>, C<discard>, and C<autodefer> | |
2287 | ||
2288 | See L<"Deferred Writing">, below. | |
2289 | ||
2290 | =head2 C<offset> | |
2291 | ||
2292 | $off = $o->offset($n); | |
2293 | ||
2294 | This method returns the byte offset of the start of the C<$n>th record | |
2295 | in the file. If there is no such record, it returns an undefined | |
2296 | value. | |
2297 | ||
2298 | =head1 Tying to an already-opened filehandle | |
2299 | ||
2300 | If C<$fh> is a filehandle, such as is returned by C<IO::File> or one | |
2301 | of the other C<IO> modules, you may use: | |
2302 | ||
2303 | tie @array, 'Tie::File', $fh, ...; | |
2304 | ||
2305 | Similarly if you opened that handle C<FH> with regular C<open> or | |
2306 | C<sysopen>, you may use: | |
2307 | ||
2308 | tie @array, 'Tie::File', \*FH, ...; | |
2309 | ||
2310 | Handles that were opened write-only won't work. Handles that were | |
2311 | opened read-only will work as long as you don't try to modify the | |
2312 | array. Handles must be attached to seekable sources of data---that | |
2313 | means no pipes or sockets. If C<Tie::File> can detect that you | |
2314 | supplied a non-seekable handle, the C<tie> call will throw an | |
2315 | exception. (On Unix systems, it can detect this.) | |
2316 | ||
2317 | Note that Tie::File will only close any filehandles that it opened | |
2318 | internally. If you passed it a filehandle as above, you "own" the | |
2319 | filehandle, and are responsible for closing it after you have untied | |
2320 | the @array. | |
2321 | ||
2322 | =head1 Deferred Writing | |
2323 | ||
2324 | (This is an advanced feature. Skip this section on first reading.) | |
2325 | ||
2326 | Normally, modifying a C<Tie::File> array writes to the underlying file | |
2327 | immediately. Every assignment like C<$a[3] = ...> rewrites as much of | |
2328 | the file as is necessary; typically, everything from line 3 through | |
2329 | the end will need to be rewritten. This is the simplest and most | |
2330 | transparent behavior. Performance even for large files is reasonably | |
2331 | good. | |
2332 | ||
2333 | However, under some circumstances, this behavior may be excessively | |
2334 | slow. For example, suppose you have a million-record file, and you | |
2335 | want to do: | |
2336 | ||
2337 | for (@FILE) { | |
2338 | $_ = "> $_"; | |
2339 | } | |
2340 | ||
2341 | The first time through the loop, you will rewrite the entire file, | |
2342 | from line 0 through the end. The second time through the loop, you | |
2343 | will rewrite the entire file from line 1 through the end. The third | |
2344 | time through the loop, you will rewrite the entire file from line 2 to | |
2345 | the end. And so on. | |
2346 | ||
2347 | If the performance in such cases is unacceptable, you may defer the | |
2348 | actual writing, and then have it done all at once. The following loop | |
2349 | will perform much better for large files: | |
2350 | ||
2351 | (tied @a)->defer; | |
2352 | for (@a) { | |
2353 | $_ = "> $_"; | |
2354 | } | |
2355 | (tied @a)->flush; | |
2356 | ||
2357 | If C<Tie::File>'s memory limit is large enough, all the writing will | |
2358 | done in memory. Then, when you call C<-E<gt>flush>, the entire file | |
2359 | will be rewritten in a single pass. | |
2360 | ||
2361 | (Actually, the preceding discussion is something of a fib. You don't | |
2362 | need to enable deferred writing to get good performance for this | |
2363 | common case, because C<Tie::File> will do it for you automatically | |
2364 | unless you specifically tell it not to. See L<"autodeferring">, | |
2365 | below.) | |
2366 | ||
2367 | Calling C<-E<gt>flush> returns the array to immediate-write mode. If | |
2368 | you wish to discard the deferred writes, you may call C<-E<gt>discard> | |
2369 | instead of C<-E<gt>flush>. Note that in some cases, some of the data | |
2370 | will have been written already, and it will be too late for | |
2371 | C<-E<gt>discard> to discard all the changes. Support for | |
2372 | C<-E<gt>discard> may be withdrawn in a future version of C<Tie::File>. | |
2373 | ||
2374 | Deferred writes are cached in memory up to the limit specified by the | |
2375 | C<dw_size> option (see above). If the deferred-write buffer is full | |
2376 | and you try to write still more deferred data, the buffer will be | |
2377 | flushed. All buffered data will be written immediately, the buffer | |
2378 | will be emptied, and the now-empty space will be used for future | |
2379 | deferred writes. | |
2380 | ||
2381 | If the deferred-write buffer isn't yet full, but the total size of the | |
2382 | buffer and the read cache would exceed the C<memory> limit, the oldest | |
2383 | records will be expired from the read cache until the total size is | |
2384 | under the limit. | |
2385 | ||
2386 | C<push>, C<pop>, C<shift>, C<unshift>, and C<splice> cannot be | |
2387 | deferred. When you perform one of these operations, any deferred data | |
2388 | is written to the file and the operation is performed immediately. | |
2389 | This may change in a future version. | |
2390 | ||
2391 | If you resize the array with deferred writing enabled, the file will | |
2392 | be resized immediately, but deferred records will not be written. | |
2393 | This has a surprising consequence: C<@a = (...)> erases the file | |
2394 | immediately, but the writing of the actual data is deferred. This | |
2395 | might be a bug. If it is a bug, it will be fixed in a future version. | |
2396 | ||
2397 | =head2 Autodeferring | |
2398 | ||
2399 | C<Tie::File> tries to guess when deferred writing might be helpful, | |
2400 | and to turn it on and off automatically. | |
2401 | ||
2402 | for (@a) { | |
2403 | $_ = "> $_"; | |
2404 | } | |
2405 | ||
2406 | In this example, only the first two assignments will be done | |
2407 | immediately; after this, all the changes to the file will be deferred | |
2408 | up to the user-specified memory limit. | |
2409 | ||
2410 | You should usually be able to ignore this and just use the module | |
2411 | without thinking about deferring. However, special applications may | |
2412 | require fine control over which writes are deferred, or may require | |
2413 | that all writes be immediate. To disable the autodeferment feature, | |
2414 | use | |
2415 | ||
2416 | (tied @o)->autodefer(0); | |
2417 | ||
2418 | or | |
2419 | ||
2420 | tie @array, 'Tie::File', $file, autodefer => 0; | |
2421 | ||
2422 | ||
2423 | Similarly, C<-E<gt>autodefer(1)> re-enables autodeferment, and | |
2424 | C<-E<gt>autodefer()> recovers the current value of the autodefer setting. | |
2425 | ||
2426 | ||
2427 | =head1 CONCURRENT ACCESS TO FILES | |
2428 | ||
2429 | Caching and deferred writing are inappropriate if you want the same | |
2430 | file to be accessed simultaneously from more than one process. Other | |
2431 | optimizations performed internally by this module are also | |
2432 | incompatible with concurrent access. A future version of this module will | |
2433 | support a C<concurrent =E<gt> 1> option that enables safe concurrent access. | |
2434 | ||
2435 | Previous versions of this documentation suggested using C<memory | |
2436 | =E<gt> 0> for safe concurrent access. This was mistaken. Tie::File | |
2437 | will not support safe concurrent access before version 0.98. | |
2438 | ||
2439 | =head1 CAVEATS | |
2440 | ||
2441 | (That's Latin for 'warnings'.) | |
2442 | ||
2443 | =over 4 | |
2444 | ||
2445 | =item * | |
2446 | ||
2447 | Reasonable effort was made to make this module efficient. Nevertheless, | |
2448 | changing the size of a record in the middle of a large file will | |
2449 | always be fairly slow, because everything after the new record must be | |
2450 | moved. | |
2451 | ||
2452 | =item * | |
2453 | ||
2454 | The behavior of tied arrays is not precisely the same as for regular | |
2455 | arrays. For example: | |
2456 | ||
2457 | # This DOES print "How unusual!" | |
2458 | undef $a[10]; print "How unusual!\n" if defined $a[10]; | |
2459 | ||
2460 | C<undef>-ing a C<Tie::File> array element just blanks out the | |
2461 | corresponding record in the file. When you read it back again, you'll | |
2462 | get the empty string, so the supposedly-C<undef>'ed value will be | |
2463 | defined. Similarly, if you have C<autochomp> disabled, then | |
2464 | ||
2465 | # This DOES print "How unusual!" if 'autochomp' is disabled | |
2466 | undef $a[10]; | |
2467 | print "How unusual!\n" if $a[10]; | |
2468 | ||
2469 | Because when C<autochomp> is disabled, C<$a[10]> will read back as | |
2470 | C<"\n"> (or whatever the record separator string is.) | |
2471 | ||
2472 | There are other minor differences, particularly regarding C<exists> | |
2473 | and C<delete>, but in general, the correspondence is extremely close. | |
2474 | ||
2475 | =item * | |
2476 | ||
2477 | I have supposed that since this module is concerned with file I/O, | |
2478 | almost all normal use of it will be heavily I/O bound. This means | |
2479 | that the time to maintain complicated data structures inside the | |
2480 | module will be dominated by the time to actually perform the I/O. | |
2481 | When there was an opportunity to spend CPU time to avoid doing I/O, I | |
2482 | usually tried to take it. | |
2483 | ||
2484 | =item * | |
2485 | ||
2486 | You might be tempted to think that deferred writing is like | |
2487 | transactions, with C<flush> as C<commit> and C<discard> as | |
2488 | C<rollback>, but it isn't, so don't. | |
2489 | ||
2490 | =item * | |
2491 | ||
2492 | There is a large memory overhead for each record offset and for each | |
2493 | cache entry: about 310 bytes per cached data record, and about 21 bytes per offset table entry. | |
2494 | ||
2495 | The per-record overhead will limit the maximum number of records you | |
2496 | can access per file. Note that I<accessing> the length of the array | |
2497 | via C<$x = scalar @tied_file> accesses B<all> records and stores their | |
2498 | offsets. The same for C<foreach (@tied_file)>, even if you exit the | |
2499 | loop early. | |
2500 | ||
2501 | =back | |
2502 | ||
2503 | =head1 SUBCLASSING | |
2504 | ||
2505 | This version promises absolutely nothing about the internals, which | |
2506 | may change without notice. A future version of the module will have a | |
2507 | well-defined and stable subclassing API. | |
2508 | ||
2509 | =head1 WHAT ABOUT C<DB_File>? | |
2510 | ||
2511 | People sometimes point out that L<DB_File> will do something similar, | |
2512 | and ask why C<Tie::File> module is necessary. | |
2513 | ||
2514 | There are a number of reasons that you might prefer C<Tie::File>. | |
2515 | A list is available at C<http://perl.plover.com/TieFile/why-not-DB_File>. | |
2516 | ||
2517 | =head1 AUTHOR | |
2518 | ||
2519 | Mark Jason Dominus | |
2520 | ||
2521 | To contact the author, send email to: C<mjd-perl-tiefile+@plover.com> | |
2522 | ||
2523 | To receive an announcement whenever a new version of this module is | |
2524 | released, send a blank email message to | |
2525 | C<mjd-perl-tiefile-subscribe@plover.com>. | |
2526 | ||
2527 | The most recent version of this module, including documentation and | |
2528 | any news of importance, will be available at | |
2529 | ||
2530 | http://perl.plover.com/TieFile/ | |
2531 | ||
2532 | ||
2533 | =head1 LICENSE | |
2534 | ||
2535 | C<Tie::File> version 0.97 is copyright (C) 2003 Mark Jason Dominus. | |
2536 | ||
2537 | This library is free software; you may redistribute it and/or modify | |
2538 | it under the same terms as Perl itself. | |
2539 | ||
2540 | These terms are your choice of any of (1) the Perl Artistic Licence, | |
2541 | or (2) version 2 of the GNU General Public License as published by the | |
2542 | Free Software Foundation, or (3) any later version of the GNU General | |
2543 | Public License. | |
2544 | ||
2545 | This library is distributed in the hope that it will be useful, | |
2546 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
2547 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
2548 | GNU General Public License for more details. | |
2549 | ||
2550 | You should have received a copy of the GNU General Public License | |
2551 | along with this library program; it should be in the file C<COPYING>. | |
2552 | If not, write to the Free Software Foundation, Inc., 59 Temple Place, | |
2553 | Suite 330, Boston, MA 02111 USA | |
2554 | ||
2555 | For licensing inquiries, contact the author at: | |
2556 | ||
2557 | Mark Jason Dominus | |
2558 | 255 S. Warnock St. | |
2559 | Philadelphia, PA 19107 | |
2560 | ||
2561 | =head1 WARRANTY | |
2562 | ||
2563 | C<Tie::File> version 0.97 comes with ABSOLUTELY NO WARRANTY. | |
2564 | For details, see the license. | |
2565 | ||
2566 | =head1 THANKS | |
2567 | ||
2568 | Gigantic thanks to Jarkko Hietaniemi, for agreeing to put this in the | |
2569 | core when I hadn't written it yet, and for generally being helpful, | |
2570 | supportive, and competent. (Usually the rule is "choose any one.") | |
2571 | Also big thanks to Abhijit Menon-Sen for all of the same things. | |
2572 | ||
2573 | Special thanks to Craig Berry and Peter Prymmer (for VMS portability | |
2574 | help), Randy Kobes (for Win32 portability help), Clinton Pierce and | |
2575 | Autrijus Tang (for heroic eleventh-hour Win32 testing above and beyond | |
2576 | the call of duty), Michael G Schwern (for testing advice), and the | |
2577 | rest of the CPAN testers (for testing generally). | |
2578 | ||
2579 | Special thanks to Tels for suggesting several speed and memory | |
2580 | optimizations. | |
2581 | ||
2582 | Additional thanks to: | |
2583 | Edward Avis / | |
2584 | Mattia Barbon / | |
2585 | Tom Christiansen / | |
2586 | Gerrit Haase / | |
2587 | Gurusamy Sarathy / | |
2588 | Jarkko Hietaniemi (again) / | |
2589 | Nikola Knezevic / | |
2590 | John Kominetz / | |
2591 | Nick Ing-Simmons / | |
2592 | Tassilo von Parseval / | |
2593 | H. Dieter Pearcey / | |
2594 | Slaven Rezic / | |
2595 | Eric Roode / | |
2596 | Peter Scott / | |
2597 | Peter Somu / | |
2598 | Autrijus Tang (again) / | |
2599 | Tels (again) / | |
2600 | Juerd Waalboer | |
2601 | ||
2602 | =head1 TODO | |
2603 | ||
2604 | More tests. (Stuff I didn't think of yet.) | |
2605 | ||
2606 | Paragraph mode? | |
2607 | ||
2608 | Fixed-length mode. Leave-blanks mode. | |
2609 | ||
2610 | Maybe an autolocking mode? | |
2611 | ||
2612 | For many common uses of the module, the read cache is a liability. | |
2613 | For example, a program that inserts a single record, or that scans the | |
2614 | file once, will have a cache hit rate of zero. This suggests a major | |
2615 | optimization: The cache should be initially disabled. Here's a hybrid | |
2616 | approach: Initially, the cache is disabled, but the cache code | |
2617 | maintains statistics about how high the hit rate would be *if* it were | |
2618 | enabled. When it sees the hit rate get high enough, it enables | |
2619 | itself. The STAT comments in this code are the beginning of an | |
2620 | implementation of this. | |
2621 | ||
2622 | Record locking with fcntl()? Then the module might support an undo | |
2623 | log and get real transactions. What a tour de force that would be. | |
2624 | ||
2625 | Keeping track of the highest cached record. This would allow reads-in-a-row | |
2626 | to skip the cache lookup faster (if reading from 1..N with empty cache at | |
2627 | start, the last cached value will be always N-1). | |
2628 | ||
2629 | More tests. | |
2630 | ||
2631 | =cut | |
2632 |