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1 | package threads::shared; |
2 | ||
3 | use 5.007_003; | |
4 | use strict; | |
5 | use warnings; | |
6 | ||
7 | require Exporter; | |
8 | our @ISA = qw(Exporter); | |
9 | our @EXPORT = qw(share cond_wait cond_broadcast cond_signal _refcnt _id _thrcnt); | |
10 | our $VERSION = '0.90'; | |
11 | ||
12 | if ($threads::threads) { | |
13 | *cond_wait = \&cond_wait_enabled; | |
14 | *cond_signal = \&cond_signal_enabled; | |
15 | *cond_broadcast = \&cond_broadcast_enabled; | |
16 | require XSLoader; | |
17 | XSLoader::load('threads::shared',$VERSION); | |
18 | } | |
19 | else { | |
20 | *share = \&share_disabled; | |
21 | *cond_wait = \&cond_wait_disabled; | |
22 | *cond_signal = \&cond_signal_disabled; | |
23 | *cond_broadcast = \&cond_broadcast_disabled; | |
24 | } | |
25 | ||
26 | ||
27 | sub cond_wait_disabled { return @_ }; | |
28 | sub cond_signal_disabled { return @_}; | |
29 | sub cond_broadcast_disabled { return @_}; | |
30 | sub share_disabled { return @_} | |
31 | ||
32 | $threads::shared::threads_shared = 1; | |
33 | ||
34 | ||
35 | sub threads::shared::tie::SPLICE | |
36 | { | |
37 | die "Splice not implemented for shared arrays"; | |
38 | } | |
39 | ||
40 | __END__ | |
41 | ||
42 | =head1 NAME | |
43 | ||
44 | threads::shared - Perl extension for sharing data structures between threads | |
45 | ||
46 | =head1 SYNOPSIS | |
47 | ||
48 | use threads; | |
49 | use threads::shared; | |
50 | ||
51 | my $var : shared; | |
52 | ||
53 | my($scalar, @array, %hash); | |
54 | share($scalar); | |
55 | share(@array); | |
56 | share(%hash); | |
57 | my $bar = &share([]); | |
58 | $hash{bar} = &share({}); | |
59 | ||
60 | { lock(%hash); ... } | |
61 | ||
62 | cond_wait($scalar); | |
63 | cond_broadcast(@array); | |
64 | cond_signal(%hash); | |
65 | ||
66 | =head1 DESCRIPTION | |
67 | ||
68 | By default, variables are private to each thread, and each newly created | |
69 | thread gets a private copy of each existing variable. This module allows | |
70 | you to share variables across different threads (and pseudoforks on Win32). | |
71 | It is used together with the threads module. | |
72 | ||
73 | =head1 EXPORT | |
74 | ||
75 | C<share>, C<lock>, C<cond_wait>, C<cond_signal>, C<cond_broadcast> | |
76 | ||
77 | Note that if this module is imported when C<threads> has not yet been | |
78 | loaded, then these functions all become no-ops. This makes it possible | |
79 | to write modules that will work in both threaded and non-threaded | |
80 | environments. | |
81 | ||
82 | =head1 FUNCTIONS | |
83 | ||
84 | =over 4 | |
85 | ||
86 | =item share VARIABLE | |
87 | ||
88 | C<share> takes a value and marks it as shared. You can share a scalar, | |
89 | array, hash, scalar ref, array ref or hash ref. C<share> will return | |
90 | the shared rvalue. | |
91 | ||
92 | C<share> will traverse up references exactly I<one> level. | |
93 | C<share(\$a)> is equivalent to C<share($a)>, while C<share(\\$a)> is not. | |
94 | ||
95 | A variable can also be marked as shared at compile time by using the | |
96 | C<shared> attribute: C<my $var : shared>. | |
97 | ||
98 | If you want to share a newly created reference unfortunately you | |
99 | need to use C<&share([])> and C<&share({})> syntax due to problems | |
100 | with Perl's prototyping. | |
101 | ||
102 | =item lock VARIABLE | |
103 | ||
104 | C<lock> places a lock on a variable until the lock goes out of scope. | |
105 | If the variable is locked by another thread, the C<lock> call will | |
106 | block until it's available. C<lock> is recursive, so multiple calls | |
107 | to C<lock> are safe -- the variable will remain locked until the | |
108 | outermost lock on the variable goes out of scope. | |
109 | ||
110 | If a container object, such as a hash or array, is locked, all the | |
111 | elements of that container are not locked. For example, if a thread | |
112 | does a C<lock @a>, any other thread doing a C<lock($a[12])> won't block. | |
113 | ||
114 | C<lock> will traverse up references exactly I<one> level. | |
115 | C<lock(\$a)> is equivalent to C<lock($a)>, while C<lock(\\$a)> is not. | |
116 | ||
117 | Note that you cannot explicitly unlock a variable; you can only wait | |
118 | for the lock to go out of scope. If you need more fine-grained | |
119 | control, see L<Thread::Semaphore>. | |
120 | ||
121 | =item cond_wait VARIABLE | |
122 | ||
123 | The C<cond_wait> function takes a B<locked> variable as a parameter, | |
124 | unlocks the variable, and blocks until another thread does a | |
125 | C<cond_signal> or C<cond_broadcast> for that same locked variable. | |
126 | The variable that C<cond_wait> blocked on is relocked after the | |
127 | C<cond_wait> is satisfied. If there are multiple threads | |
128 | C<cond_wait>ing on the same variable, all but one will reblock waiting | |
129 | to reacquire the lock on the variable. (So if you're only using | |
130 | C<cond_wait> for synchronisation, give up the lock as soon as | |
131 | possible). The two actions of unlocking the variable and entering the | |
132 | blocked wait state are atomic, The two actions of exiting from the | |
133 | blocked wait state and relocking the variable are not. | |
134 | ||
135 | It is important to note that the variable can be notified even if | |
136 | no thread C<cond_signal> or C<cond_broadcast> on the variable. | |
137 | It is therefore important to check the value of the variable and | |
138 | go back to waiting if the requirement is not fulfilled. | |
139 | ||
140 | =item cond_signal VARIABLE | |
141 | ||
142 | The C<cond_signal> function takes a B<locked> variable as a parameter | |
143 | and unblocks one thread that's C<cond_wait>ing on that variable. If | |
144 | more than one thread is blocked in a C<cond_wait> on that variable, | |
145 | only one (and which one is indeterminate) will be unblocked. | |
146 | ||
147 | If there are no threads blocked in a C<cond_wait> on the variable, | |
148 | the signal is discarded. By always locking before signaling, you can | |
149 | (with care), avoid signaling before another thread has entered cond_wait(). | |
150 | ||
151 | C<cond_signal> will normally generate a warning if you attempt to use it | |
152 | on an unlocked variable. On the rare occasions where doing this may be | |
153 | sensible, you can skip the warning with | |
154 | ||
155 | { no warnings 'threads'; cond_signal($foo) } | |
156 | ||
157 | =item cond_broadcast VARIABLE | |
158 | ||
159 | The C<cond_broadcast> function works similarly to C<cond_signal>. | |
160 | C<cond_broadcast>, though, will unblock B<all> the threads that are | |
161 | blocked in a C<cond_wait> on the locked variable, rather than only one. | |
162 | ||
163 | =back | |
164 | ||
165 | =head1 NOTES | |
166 | ||
167 | threads::shared is designed to disable itself silently if threads are | |
168 | not available. If you want access to threads, you must C<use threads> | |
169 | before you C<use threads::shared>. threads will emit a warning if you | |
170 | use it after threads::shared. | |
171 | ||
172 | =head1 BUGS | |
173 | ||
174 | C<bless> is not supported on shared references. In the current version, | |
175 | C<bless> will only bless the thread local reference and the blessing | |
176 | will not propagate to the other threads. This is expected to be | |
177 | implemented in a future version of Perl. | |
178 | ||
179 | Does not support splice on arrays! | |
180 | ||
181 | Taking references to the elements of shared arrays and hashes does not | |
182 | autovivify the elements, and neither does slicing a shared array/hash | |
183 | over non-existent indices/keys autovivify the elements. | |
184 | ||
185 | share() allows you to C<share $hashref->{key}> without giving any error | |
186 | message. But the C<$hashref->{key}> is B<not> shared, causing the error | |
187 | "locking can only be used on shared values" to occur when you attempt to | |
188 | C<lock $hasref->{key}>. | |
189 | ||
190 | =head1 AUTHOR | |
191 | ||
192 | Arthur Bergman E<lt>arthur at contiller.seE<gt> | |
193 | ||
194 | threads::shared is released under the same license as Perl | |
195 | ||
196 | Documentation borrowed from the old Thread.pm | |
197 | ||
198 | =head1 SEE ALSO | |
199 | ||
200 | L<threads>, L<perlthrtut>, L<http://www.perl.com/pub/a/2002/06/11/threads.html> | |
201 | ||
202 | =cut |