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b688fc87 WJ |
1 | /* |
2 | * Copyright (c) 1991 Regents of the University of California. | |
3 | * All rights reserved. | |
4 | * | |
5 | * This code is derived from software contributed to Berkeley by | |
6 | * The Mach Operating System project at Carnegie-Mellon University. | |
7 | * | |
8 | * Redistribution and use in source and binary forms, with or without | |
9 | * modification, are permitted provided that the following conditions | |
10 | * are met: | |
11 | * 1. Redistributions of source code must retain the above copyright | |
12 | * notice, this list of conditions and the following disclaimer. | |
13 | * 2. Redistributions in binary form must reproduce the above copyright | |
14 | * notice, this list of conditions and the following disclaimer in the | |
15 | * documentation and/or other materials provided with the distribution. | |
16 | * 3. All advertising materials mentioning features or use of this software | |
17 | * must display the following acknowledgement: | |
18 | * This product includes software developed by the University of | |
19 | * California, Berkeley and its contributors. | |
20 | * 4. Neither the name of the University nor the names of its contributors | |
21 | * may be used to endorse or promote products derived from this software | |
22 | * without specific prior written permission. | |
23 | * | |
24 | * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND | |
25 | * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE | |
26 | * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE | |
27 | * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE | |
28 | * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL | |
29 | * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS | |
30 | * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) | |
31 | * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT | |
32 | * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY | |
33 | * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF | |
34 | * SUCH DAMAGE. | |
35 | * | |
36 | * @(#)kern_lock.c 7.4 (Berkeley) 4/21/91 | |
37 | * | |
38 | * | |
39 | * Copyright (c) 1987, 1990 Carnegie-Mellon University. | |
40 | * All rights reserved. | |
41 | * | |
42 | * Authors: Avadis Tevanian, Jr., Michael Wayne Young | |
43 | * | |
44 | * Permission to use, copy, modify and distribute this software and | |
45 | * its documentation is hereby granted, provided that both the copyright | |
46 | * notice and this permission notice appear in all copies of the | |
47 | * software, derivative works or modified versions, and any portions | |
48 | * thereof, and that both notices appear in supporting documentation. | |
49 | * | |
50 | * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS" | |
51 | * CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND | |
52 | * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE. | |
53 | * | |
54 | * Carnegie Mellon requests users of this software to return to | |
55 | * | |
56 | * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU | |
57 | * School of Computer Science | |
58 | * Carnegie Mellon University | |
59 | * Pittsburgh PA 15213-3890 | |
60 | * | |
61 | * any improvements or extensions that they make and grant Carnegie the | |
62 | * rights to redistribute these changes. | |
63 | */ | |
64 | ||
65 | /* | |
66 | * Locking primitives implementation | |
67 | */ | |
68 | ||
69 | #include "param.h" | |
70 | #include "vm_param.h" | |
71 | #include "lock.h" | |
72 | ||
73 | /* XXX */ | |
74 | #include "proc.h" | |
75 | typedef int *thread_t; | |
76 | #define current_thread() ((thread_t)&curproc->p_thread) | |
77 | /* XXX */ | |
78 | ||
79 | #if NCPUS > 1 | |
80 | ||
81 | /* | |
82 | * Module: lock | |
83 | * Function: | |
84 | * Provide reader/writer sychronization. | |
85 | * Implementation: | |
86 | * Simple interlock on a bit. Readers first interlock | |
87 | * increment the reader count, then let go. Writers hold | |
88 | * the interlock (thus preventing further readers), and | |
89 | * wait for already-accepted readers to go away. | |
90 | */ | |
91 | ||
92 | /* | |
93 | * The simple-lock routines are the primitives out of which | |
94 | * the lock package is built. The implementation is left | |
95 | * to the machine-dependent code. | |
96 | */ | |
97 | ||
98 | #ifdef notdef | |
99 | /* | |
100 | * A sample implementation of simple locks. | |
101 | * assumes: | |
102 | * boolean_t test_and_set(boolean_t *) | |
103 | * indivisibly sets the boolean to TRUE | |
104 | * and returns its old value | |
105 | * and that setting a boolean to FALSE is indivisible. | |
106 | */ | |
107 | /* | |
108 | * simple_lock_init initializes a simple lock. A simple lock | |
109 | * may only be used for exclusive locks. | |
110 | */ | |
111 | ||
112 | void simple_lock_init(l) | |
113 | simple_lock_t l; | |
114 | { | |
115 | *(boolean_t *)l = FALSE; | |
116 | } | |
117 | ||
118 | void simple_lock(l) | |
119 | simple_lock_t l; | |
120 | { | |
121 | while (test_and_set((boolean_t *)l)) | |
122 | continue; | |
123 | } | |
124 | ||
125 | void simple_unlock(l) | |
126 | simple_lock_t l; | |
127 | { | |
128 | *(boolean_t *)l = FALSE; | |
129 | } | |
130 | ||
131 | boolean_t simple_lock_try(l) | |
132 | simple_lock_t l; | |
133 | { | |
134 | return (!test_and_set((boolean_t *)l)); | |
135 | } | |
136 | #endif notdef | |
137 | #endif NCPUS > 1 | |
138 | ||
139 | #if NCPUS > 1 | |
140 | int lock_wait_time = 100; | |
141 | #else NCPUS > 1 | |
142 | ||
143 | /* | |
144 | * It is silly to spin on a uni-processor as if we | |
145 | * thought something magical would happen to the | |
146 | * want_write bit while we are executing. | |
147 | */ | |
148 | int lock_wait_time = 0; | |
149 | #endif NCPUS > 1 | |
150 | ||
151 | ||
152 | /* | |
153 | * Routine: lock_init | |
154 | * Function: | |
155 | * Initialize a lock; required before use. | |
156 | * Note that clients declare the "struct lock" | |
157 | * variables and then initialize them, rather | |
158 | * than getting a new one from this module. | |
159 | */ | |
160 | void lock_init(l, can_sleep) | |
161 | lock_t l; | |
162 | boolean_t can_sleep; | |
163 | { | |
164 | bzero(l, sizeof(lock_data_t)); | |
165 | simple_lock_init(&l->interlock); | |
166 | l->want_write = FALSE; | |
167 | l->want_upgrade = FALSE; | |
168 | l->read_count = 0; | |
169 | l->can_sleep = can_sleep; | |
170 | l->thread = (char *)-1; /* XXX */ | |
171 | l->recursion_depth = 0; | |
172 | } | |
173 | ||
174 | void lock_sleepable(l, can_sleep) | |
175 | lock_t l; | |
176 | boolean_t can_sleep; | |
177 | { | |
178 | simple_lock(&l->interlock); | |
179 | l->can_sleep = can_sleep; | |
180 | simple_unlock(&l->interlock); | |
181 | } | |
182 | ||
183 | ||
184 | /* | |
185 | * Sleep locks. These use the same data structure and algorithm | |
186 | * as the spin locks, but the process sleeps while it is waiting | |
187 | * for the lock. These work on uniprocessor systems. | |
188 | */ | |
189 | ||
190 | void lock_write(l) | |
191 | register lock_t l; | |
192 | { | |
193 | register int i; | |
194 | ||
195 | simple_lock(&l->interlock); | |
196 | ||
197 | if (((thread_t)l->thread) == current_thread()) { | |
198 | /* | |
199 | * Recursive lock. | |
200 | */ | |
201 | l->recursion_depth++; | |
202 | simple_unlock(&l->interlock); | |
203 | return; | |
204 | } | |
205 | ||
206 | /* | |
207 | * Try to acquire the want_write bit. | |
208 | */ | |
209 | while (l->want_write) { | |
210 | if ((i = lock_wait_time) > 0) { | |
211 | simple_unlock(&l->interlock); | |
212 | while (--i > 0 && l->want_write) | |
213 | continue; | |
214 | simple_lock(&l->interlock); | |
215 | } | |
216 | ||
217 | if (l->can_sleep && l->want_write) { | |
218 | l->waiting = TRUE; | |
219 | thread_sleep((int) l, &l->interlock, FALSE); | |
220 | simple_lock(&l->interlock); | |
221 | } | |
222 | } | |
223 | l->want_write = TRUE; | |
224 | ||
225 | /* Wait for readers (and upgrades) to finish */ | |
226 | ||
227 | while ((l->read_count != 0) || l->want_upgrade) { | |
228 | if ((i = lock_wait_time) > 0) { | |
229 | simple_unlock(&l->interlock); | |
230 | while (--i > 0 && (l->read_count != 0 || | |
231 | l->want_upgrade)) | |
232 | continue; | |
233 | simple_lock(&l->interlock); | |
234 | } | |
235 | ||
236 | if (l->can_sleep && (l->read_count != 0 || l->want_upgrade)) { | |
237 | l->waiting = TRUE; | |
238 | thread_sleep((int) l, &l->interlock, FALSE); | |
239 | simple_lock(&l->interlock); | |
240 | } | |
241 | } | |
242 | simple_unlock(&l->interlock); | |
243 | } | |
244 | ||
245 | void lock_done(l) | |
246 | register lock_t l; | |
247 | { | |
248 | simple_lock(&l->interlock); | |
249 | ||
250 | if (l->read_count != 0) | |
251 | l->read_count--; | |
252 | else | |
253 | if (l->recursion_depth != 0) | |
254 | l->recursion_depth--; | |
255 | else | |
256 | if (l->want_upgrade) | |
257 | l->want_upgrade = FALSE; | |
258 | else | |
259 | l->want_write = FALSE; | |
260 | ||
261 | if (l->waiting) { | |
262 | l->waiting = FALSE; | |
263 | thread_wakeup((int) l); | |
264 | } | |
265 | simple_unlock(&l->interlock); | |
266 | } | |
267 | ||
268 | void lock_read(l) | |
269 | register lock_t l; | |
270 | { | |
271 | register int i; | |
272 | ||
273 | simple_lock(&l->interlock); | |
274 | ||
275 | if (((thread_t)l->thread) == current_thread()) { | |
276 | /* | |
277 | * Recursive lock. | |
278 | */ | |
279 | l->read_count++; | |
280 | simple_unlock(&l->interlock); | |
281 | return; | |
282 | } | |
283 | ||
284 | while (l->want_write || l->want_upgrade) { | |
285 | if ((i = lock_wait_time) > 0) { | |
286 | simple_unlock(&l->interlock); | |
287 | while (--i > 0 && (l->want_write || l->want_upgrade)) | |
288 | continue; | |
289 | simple_lock(&l->interlock); | |
290 | } | |
291 | ||
292 | if (l->can_sleep && (l->want_write || l->want_upgrade)) { | |
293 | l->waiting = TRUE; | |
294 | thread_sleep((int) l, &l->interlock, FALSE); | |
295 | simple_lock(&l->interlock); | |
296 | } | |
297 | } | |
298 | ||
299 | l->read_count++; | |
300 | simple_unlock(&l->interlock); | |
301 | } | |
302 | ||
303 | /* | |
304 | * Routine: lock_read_to_write | |
305 | * Function: | |
306 | * Improves a read-only lock to one with | |
307 | * write permission. If another reader has | |
308 | * already requested an upgrade to a write lock, | |
309 | * no lock is held upon return. | |
310 | * | |
311 | * Returns TRUE if the upgrade *failed*. | |
312 | */ | |
313 | boolean_t lock_read_to_write(l) | |
314 | register lock_t l; | |
315 | { | |
316 | register int i; | |
317 | ||
318 | simple_lock(&l->interlock); | |
319 | ||
320 | l->read_count--; | |
321 | ||
322 | if (((thread_t)l->thread) == current_thread()) { | |
323 | /* | |
324 | * Recursive lock. | |
325 | */ | |
326 | l->recursion_depth++; | |
327 | simple_unlock(&l->interlock); | |
328 | return(FALSE); | |
329 | } | |
330 | ||
331 | if (l->want_upgrade) { | |
332 | /* | |
333 | * Someone else has requested upgrade. | |
334 | * Since we've released a read lock, wake | |
335 | * him up. | |
336 | */ | |
337 | if (l->waiting) { | |
338 | l->waiting = FALSE; | |
339 | thread_wakeup((int) l); | |
340 | } | |
341 | ||
342 | simple_unlock(&l->interlock); | |
343 | return (TRUE); | |
344 | } | |
345 | ||
346 | l->want_upgrade = TRUE; | |
347 | ||
348 | while (l->read_count != 0) { | |
349 | if ((i = lock_wait_time) > 0) { | |
350 | simple_unlock(&l->interlock); | |
351 | while (--i > 0 && l->read_count != 0) | |
352 | continue; | |
353 | simple_lock(&l->interlock); | |
354 | } | |
355 | ||
356 | if (l->can_sleep && l->read_count != 0) { | |
357 | l->waiting = TRUE; | |
358 | thread_sleep((int) l, &l->interlock, FALSE); | |
359 | simple_lock(&l->interlock); | |
360 | } | |
361 | } | |
362 | ||
363 | simple_unlock(&l->interlock); | |
364 | return (FALSE); | |
365 | } | |
366 | ||
367 | void lock_write_to_read(l) | |
368 | register lock_t l; | |
369 | { | |
370 | simple_lock(&l->interlock); | |
371 | ||
372 | l->read_count++; | |
373 | if (l->recursion_depth != 0) | |
374 | l->recursion_depth--; | |
375 | else | |
376 | if (l->want_upgrade) | |
377 | l->want_upgrade = FALSE; | |
378 | else | |
379 | l->want_write = FALSE; | |
380 | ||
381 | if (l->waiting) { | |
382 | l->waiting = FALSE; | |
383 | thread_wakeup((int) l); | |
384 | } | |
385 | ||
386 | simple_unlock(&l->interlock); | |
387 | } | |
388 | ||
389 | ||
390 | /* | |
391 | * Routine: lock_try_write | |
392 | * Function: | |
393 | * Tries to get a write lock. | |
394 | * | |
395 | * Returns FALSE if the lock is not held on return. | |
396 | */ | |
397 | ||
398 | boolean_t lock_try_write(l) | |
399 | register lock_t l; | |
400 | { | |
401 | ||
402 | simple_lock(&l->interlock); | |
403 | ||
404 | if (((thread_t)l->thread) == current_thread()) { | |
405 | /* | |
406 | * Recursive lock | |
407 | */ | |
408 | l->recursion_depth++; | |
409 | simple_unlock(&l->interlock); | |
410 | return(TRUE); | |
411 | } | |
412 | ||
413 | if (l->want_write || l->want_upgrade || l->read_count) { | |
414 | /* | |
415 | * Can't get lock. | |
416 | */ | |
417 | simple_unlock(&l->interlock); | |
418 | return(FALSE); | |
419 | } | |
420 | ||
421 | /* | |
422 | * Have lock. | |
423 | */ | |
424 | ||
425 | l->want_write = TRUE; | |
426 | simple_unlock(&l->interlock); | |
427 | return(TRUE); | |
428 | } | |
429 | ||
430 | /* | |
431 | * Routine: lock_try_read | |
432 | * Function: | |
433 | * Tries to get a read lock. | |
434 | * | |
435 | * Returns FALSE if the lock is not held on return. | |
436 | */ | |
437 | ||
438 | boolean_t lock_try_read(l) | |
439 | register lock_t l; | |
440 | { | |
441 | simple_lock(&l->interlock); | |
442 | ||
443 | if (((thread_t)l->thread) == current_thread()) { | |
444 | /* | |
445 | * Recursive lock | |
446 | */ | |
447 | l->read_count++; | |
448 | simple_unlock(&l->interlock); | |
449 | return(TRUE); | |
450 | } | |
451 | ||
452 | if (l->want_write || l->want_upgrade) { | |
453 | simple_unlock(&l->interlock); | |
454 | return(FALSE); | |
455 | } | |
456 | ||
457 | l->read_count++; | |
458 | simple_unlock(&l->interlock); | |
459 | return(TRUE); | |
460 | } | |
461 | ||
462 | /* | |
463 | * Routine: lock_try_read_to_write | |
464 | * Function: | |
465 | * Improves a read-only lock to one with | |
466 | * write permission. If another reader has | |
467 | * already requested an upgrade to a write lock, | |
468 | * the read lock is still held upon return. | |
469 | * | |
470 | * Returns FALSE if the upgrade *failed*. | |
471 | */ | |
472 | boolean_t lock_try_read_to_write(l) | |
473 | register lock_t l; | |
474 | { | |
475 | ||
476 | simple_lock(&l->interlock); | |
477 | ||
478 | if (((thread_t)l->thread) == current_thread()) { | |
479 | /* | |
480 | * Recursive lock | |
481 | */ | |
482 | l->read_count--; | |
483 | l->recursion_depth++; | |
484 | simple_unlock(&l->interlock); | |
485 | return(TRUE); | |
486 | } | |
487 | ||
488 | if (l->want_upgrade) { | |
489 | simple_unlock(&l->interlock); | |
490 | return(FALSE); | |
491 | } | |
492 | l->want_upgrade = TRUE; | |
493 | l->read_count--; | |
494 | ||
495 | while (l->read_count != 0) { | |
496 | l->waiting = TRUE; | |
497 | thread_sleep((int) l, &l->interlock, FALSE); | |
498 | simple_lock(&l->interlock); | |
499 | } | |
500 | ||
501 | simple_unlock(&l->interlock); | |
502 | return(TRUE); | |
503 | } | |
504 | ||
505 | /* | |
506 | * Allow a process that has a lock for write to acquire it | |
507 | * recursively (for read, write, or update). | |
508 | */ | |
509 | void lock_set_recursive(l) | |
510 | lock_t l; | |
511 | { | |
512 | simple_lock(&l->interlock); | |
513 | if (!l->want_write) { | |
514 | panic("lock_set_recursive: don't have write lock"); | |
515 | } | |
516 | l->thread = (char *) current_thread(); | |
517 | simple_unlock(&l->interlock); | |
518 | } | |
519 | ||
520 | /* | |
521 | * Prevent a lock from being re-acquired. | |
522 | */ | |
523 | void lock_clear_recursive(l) | |
524 | lock_t l; | |
525 | { | |
526 | simple_lock(&l->interlock); | |
527 | if (((thread_t) l->thread) != current_thread()) { | |
528 | panic("lock_clear_recursive: wrong thread"); | |
529 | } | |
530 | if (l->recursion_depth == 0) | |
531 | l->thread = (char *)-1; /* XXX */ | |
532 | simple_unlock(&l->interlock); | |
533 | } |