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ad787160 C |
1 | /* |
2 | * Copyright (c) 1991, 1993 | |
3 | * The Regents of the University of California. 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 8.1 (Berkeley) 6/11/93 | |
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 <sys/param.h> | |
70 | #include <sys/systm.h> | |
71 | ||
72 | #include <vm/vm.h> | |
73 | ||
74 | /* XXX */ | |
75 | #include <sys/proc.h> | |
76 | typedef int *thread_t; | |
77 | #define current_thread() ((thread_t)&curproc->p_thread) | |
78 | /* XXX */ | |
79 | ||
80 | #if NCPUS > 1 | |
81 | ||
82 | /* | |
83 | * Module: lock | |
84 | * Function: | |
85 | * Provide reader/writer sychronization. | |
86 | * Implementation: | |
87 | * Simple interlock on a bit. Readers first interlock | |
88 | * increment the reader count, then let go. Writers hold | |
89 | * the interlock (thus preventing further readers), and | |
90 | * wait for already-accepted readers to go away. | |
91 | */ | |
92 | ||
93 | /* | |
94 | * The simple-lock routines are the primitives out of which | |
95 | * the lock package is built. The implementation is left | |
96 | * to the machine-dependent code. | |
97 | */ | |
98 | ||
99 | #ifdef notdef | |
100 | /* | |
101 | * A sample implementation of simple locks. | |
102 | * assumes: | |
103 | * boolean_t test_and_set(boolean_t *) | |
104 | * indivisibly sets the boolean to TRUE | |
105 | * and returns its old value | |
106 | * and that setting a boolean to FALSE is indivisible. | |
107 | */ | |
108 | /* | |
109 | * simple_lock_init initializes a simple lock. A simple lock | |
110 | * may only be used for exclusive locks. | |
111 | */ | |
112 | ||
113 | void simple_lock_init(l) | |
114 | simple_lock_t l; | |
115 | { | |
116 | *(boolean_t *)l = FALSE; | |
117 | } | |
118 | ||
119 | void simple_lock(l) | |
120 | simple_lock_t l; | |
121 | { | |
122 | while (test_and_set((boolean_t *)l)) | |
123 | continue; | |
124 | } | |
125 | ||
126 | void simple_unlock(l) | |
127 | simple_lock_t l; | |
128 | { | |
129 | *(boolean_t *)l = FALSE; | |
130 | } | |
131 | ||
132 | boolean_t simple_lock_try(l) | |
133 | simple_lock_t l; | |
134 | { | |
135 | return (!test_and_set((boolean_t *)l)); | |
136 | } | |
137 | #endif /* notdef */ | |
138 | #endif /* NCPUS > 1 */ | |
139 | ||
140 | #if NCPUS > 1 | |
141 | int lock_wait_time = 100; | |
142 | #else /* NCPUS > 1 */ | |
143 | ||
144 | /* | |
145 | * It is silly to spin on a uni-processor as if we | |
146 | * thought something magical would happen to the | |
147 | * want_write bit while we are executing. | |
148 | */ | |
149 | int lock_wait_time = 0; | |
150 | #endif /* NCPUS > 1 */ | |
151 | ||
152 | ||
153 | /* | |
154 | * Routine: lock_init | |
155 | * Function: | |
156 | * Initialize a lock; required before use. | |
157 | * Note that clients declare the "struct lock" | |
158 | * variables and then initialize them, rather | |
159 | * than getting a new one from this module. | |
160 | */ | |
161 | void lock_init(l, can_sleep) | |
162 | lock_t l; | |
163 | boolean_t can_sleep; | |
164 | { | |
165 | bzero(l, sizeof(lock_data_t)); | |
166 | simple_lock_init(&l->interlock); | |
167 | l->want_write = FALSE; | |
168 | l->want_upgrade = FALSE; | |
169 | l->read_count = 0; | |
170 | l->can_sleep = can_sleep; | |
171 | l->thread = (char *)-1; /* XXX */ | |
172 | l->recursion_depth = 0; | |
173 | } | |
174 | ||
175 | void lock_sleepable(l, can_sleep) | |
176 | lock_t l; | |
177 | boolean_t can_sleep; | |
178 | { | |
179 | simple_lock(&l->interlock); | |
180 | l->can_sleep = can_sleep; | |
181 | simple_unlock(&l->interlock); | |
182 | } | |
183 | ||
184 | ||
185 | /* | |
186 | * Sleep locks. These use the same data structure and algorithm | |
187 | * as the spin locks, but the process sleeps while it is waiting | |
188 | * for the lock. These work on uniprocessor systems. | |
189 | */ | |
190 | ||
191 | void lock_write(l) | |
192 | register lock_t l; | |
193 | { | |
194 | register int i; | |
195 | ||
196 | simple_lock(&l->interlock); | |
197 | ||
198 | if (((thread_t)l->thread) == current_thread()) { | |
199 | /* | |
200 | * Recursive lock. | |
201 | */ | |
202 | l->recursion_depth++; | |
203 | simple_unlock(&l->interlock); | |
204 | return; | |
205 | } | |
206 | ||
207 | /* | |
208 | * Try to acquire the want_write bit. | |
209 | */ | |
210 | while (l->want_write) { | |
211 | if ((i = lock_wait_time) > 0) { | |
212 | simple_unlock(&l->interlock); | |
213 | while (--i > 0 && l->want_write) | |
214 | continue; | |
215 | simple_lock(&l->interlock); | |
216 | } | |
217 | ||
218 | if (l->can_sleep && l->want_write) { | |
219 | l->waiting = TRUE; | |
220 | thread_sleep((int) l, &l->interlock, FALSE); | |
221 | simple_lock(&l->interlock); | |
222 | } | |
223 | } | |
224 | l->want_write = TRUE; | |
225 | ||
226 | /* Wait for readers (and upgrades) to finish */ | |
227 | ||
228 | while ((l->read_count != 0) || l->want_upgrade) { | |
229 | if ((i = lock_wait_time) > 0) { | |
230 | simple_unlock(&l->interlock); | |
231 | while (--i > 0 && (l->read_count != 0 || | |
232 | l->want_upgrade)) | |
233 | continue; | |
234 | simple_lock(&l->interlock); | |
235 | } | |
236 | ||
237 | if (l->can_sleep && (l->read_count != 0 || l->want_upgrade)) { | |
238 | l->waiting = TRUE; | |
239 | thread_sleep((int) l, &l->interlock, FALSE); | |
240 | simple_lock(&l->interlock); | |
241 | } | |
242 | } | |
243 | simple_unlock(&l->interlock); | |
244 | } | |
245 | ||
246 | void lock_done(l) | |
247 | register lock_t l; | |
248 | { | |
249 | simple_lock(&l->interlock); | |
250 | ||
251 | if (l->read_count != 0) | |
252 | l->read_count--; | |
253 | else | |
254 | if (l->recursion_depth != 0) | |
255 | l->recursion_depth--; | |
256 | else | |
257 | if (l->want_upgrade) | |
258 | l->want_upgrade = FALSE; | |
259 | else | |
260 | l->want_write = FALSE; | |
261 | ||
262 | if (l->waiting) { | |
263 | l->waiting = FALSE; | |
264 | thread_wakeup((int) l); | |
265 | } | |
266 | simple_unlock(&l->interlock); | |
267 | } | |
268 | ||
269 | void lock_read(l) | |
270 | register lock_t l; | |
271 | { | |
272 | register int i; | |
273 | ||
274 | simple_lock(&l->interlock); | |
275 | ||
276 | if (((thread_t)l->thread) == current_thread()) { | |
277 | /* | |
278 | * Recursive lock. | |
279 | */ | |
280 | l->read_count++; | |
281 | simple_unlock(&l->interlock); | |
282 | return; | |
283 | } | |
284 | ||
285 | while (l->want_write || l->want_upgrade) { | |
286 | if ((i = lock_wait_time) > 0) { | |
287 | simple_unlock(&l->interlock); | |
288 | while (--i > 0 && (l->want_write || l->want_upgrade)) | |
289 | continue; | |
290 | simple_lock(&l->interlock); | |
291 | } | |
292 | ||
293 | if (l->can_sleep && (l->want_write || l->want_upgrade)) { | |
294 | l->waiting = TRUE; | |
295 | thread_sleep((int) l, &l->interlock, FALSE); | |
296 | simple_lock(&l->interlock); | |
297 | } | |
298 | } | |
299 | ||
300 | l->read_count++; | |
301 | simple_unlock(&l->interlock); | |
302 | } | |
303 | ||
304 | /* | |
305 | * Routine: lock_read_to_write | |
306 | * Function: | |
307 | * Improves a read-only lock to one with | |
308 | * write permission. If another reader has | |
309 | * already requested an upgrade to a write lock, | |
310 | * no lock is held upon return. | |
311 | * | |
312 | * Returns TRUE if the upgrade *failed*. | |
313 | */ | |
314 | boolean_t lock_read_to_write(l) | |
315 | register lock_t l; | |
316 | { | |
317 | register int i; | |
318 | ||
319 | simple_lock(&l->interlock); | |
320 | ||
321 | l->read_count--; | |
322 | ||
323 | if (((thread_t)l->thread) == current_thread()) { | |
324 | /* | |
325 | * Recursive lock. | |
326 | */ | |
327 | l->recursion_depth++; | |
328 | simple_unlock(&l->interlock); | |
329 | return(FALSE); | |
330 | } | |
331 | ||
332 | if (l->want_upgrade) { | |
333 | /* | |
334 | * Someone else has requested upgrade. | |
335 | * Since we've released a read lock, wake | |
336 | * him up. | |
337 | */ | |
338 | if (l->waiting) { | |
339 | l->waiting = FALSE; | |
340 | thread_wakeup((int) l); | |
341 | } | |
342 | ||
343 | simple_unlock(&l->interlock); | |
344 | return (TRUE); | |
345 | } | |
346 | ||
347 | l->want_upgrade = TRUE; | |
348 | ||
349 | while (l->read_count != 0) { | |
350 | if ((i = lock_wait_time) > 0) { | |
351 | simple_unlock(&l->interlock); | |
352 | while (--i > 0 && l->read_count != 0) | |
353 | continue; | |
354 | simple_lock(&l->interlock); | |
355 | } | |
356 | ||
357 | if (l->can_sleep && l->read_count != 0) { | |
358 | l->waiting = TRUE; | |
359 | thread_sleep((int) l, &l->interlock, FALSE); | |
360 | simple_lock(&l->interlock); | |
361 | } | |
362 | } | |
363 | ||
364 | simple_unlock(&l->interlock); | |
365 | return (FALSE); | |
366 | } | |
367 | ||
368 | void lock_write_to_read(l) | |
369 | register lock_t l; | |
370 | { | |
371 | simple_lock(&l->interlock); | |
372 | ||
373 | l->read_count++; | |
374 | if (l->recursion_depth != 0) | |
375 | l->recursion_depth--; | |
376 | else | |
377 | if (l->want_upgrade) | |
378 | l->want_upgrade = FALSE; | |
379 | else | |
380 | l->want_write = FALSE; | |
381 | ||
382 | if (l->waiting) { | |
383 | l->waiting = FALSE; | |
384 | thread_wakeup((int) l); | |
385 | } | |
386 | ||
387 | simple_unlock(&l->interlock); | |
388 | } | |
389 | ||
390 | ||
391 | /* | |
392 | * Routine: lock_try_write | |
393 | * Function: | |
394 | * Tries to get a write lock. | |
395 | * | |
396 | * Returns FALSE if the lock is not held on return. | |
397 | */ | |
398 | ||
399 | boolean_t lock_try_write(l) | |
400 | register lock_t l; | |
401 | { | |
402 | ||
403 | simple_lock(&l->interlock); | |
404 | ||
405 | if (((thread_t)l->thread) == current_thread()) { | |
406 | /* | |
407 | * Recursive lock | |
408 | */ | |
409 | l->recursion_depth++; | |
410 | simple_unlock(&l->interlock); | |
411 | return(TRUE); | |
412 | } | |
413 | ||
414 | if (l->want_write || l->want_upgrade || l->read_count) { | |
415 | /* | |
416 | * Can't get lock. | |
417 | */ | |
418 | simple_unlock(&l->interlock); | |
419 | return(FALSE); | |
420 | } | |
421 | ||
422 | /* | |
423 | * Have lock. | |
424 | */ | |
425 | ||
426 | l->want_write = TRUE; | |
427 | simple_unlock(&l->interlock); | |
428 | return(TRUE); | |
429 | } | |
430 | ||
431 | /* | |
432 | * Routine: lock_try_read | |
433 | * Function: | |
434 | * Tries to get a read lock. | |
435 | * | |
436 | * Returns FALSE if the lock is not held on return. | |
437 | */ | |
438 | ||
439 | boolean_t lock_try_read(l) | |
440 | register lock_t l; | |
441 | { | |
442 | simple_lock(&l->interlock); | |
443 | ||
444 | if (((thread_t)l->thread) == current_thread()) { | |
445 | /* | |
446 | * Recursive lock | |
447 | */ | |
448 | l->read_count++; | |
449 | simple_unlock(&l->interlock); | |
450 | return(TRUE); | |
451 | } | |
452 | ||
453 | if (l->want_write || l->want_upgrade) { | |
454 | simple_unlock(&l->interlock); | |
455 | return(FALSE); | |
456 | } | |
457 | ||
458 | l->read_count++; | |
459 | simple_unlock(&l->interlock); | |
460 | return(TRUE); | |
461 | } | |
462 | ||
463 | /* | |
464 | * Routine: lock_try_read_to_write | |
465 | * Function: | |
466 | * Improves a read-only lock to one with | |
467 | * write permission. If another reader has | |
468 | * already requested an upgrade to a write lock, | |
469 | * the read lock is still held upon return. | |
470 | * | |
471 | * Returns FALSE if the upgrade *failed*. | |
472 | */ | |
473 | boolean_t lock_try_read_to_write(l) | |
474 | register lock_t l; | |
475 | { | |
476 | ||
477 | simple_lock(&l->interlock); | |
478 | ||
479 | if (((thread_t)l->thread) == current_thread()) { | |
480 | /* | |
481 | * Recursive lock | |
482 | */ | |
483 | l->read_count--; | |
484 | l->recursion_depth++; | |
485 | simple_unlock(&l->interlock); | |
486 | return(TRUE); | |
487 | } | |
488 | ||
489 | if (l->want_upgrade) { | |
490 | simple_unlock(&l->interlock); | |
491 | return(FALSE); | |
492 | } | |
493 | l->want_upgrade = TRUE; | |
494 | l->read_count--; | |
495 | ||
496 | while (l->read_count != 0) { | |
497 | l->waiting = TRUE; | |
498 | thread_sleep((int) l, &l->interlock, FALSE); | |
499 | simple_lock(&l->interlock); | |
500 | } | |
501 | ||
502 | simple_unlock(&l->interlock); | |
503 | return(TRUE); | |
504 | } | |
505 | ||
506 | /* | |
507 | * Allow a process that has a lock for write to acquire it | |
508 | * recursively (for read, write, or update). | |
509 | */ | |
510 | void lock_set_recursive(l) | |
511 | lock_t l; | |
512 | { | |
513 | simple_lock(&l->interlock); | |
514 | if (!l->want_write) { | |
515 | panic("lock_set_recursive: don't have write lock"); | |
516 | } | |
517 | l->thread = (char *) current_thread(); | |
518 | simple_unlock(&l->interlock); | |
519 | } | |
520 | ||
521 | /* | |
522 | * Prevent a lock from being re-acquired. | |
523 | */ | |
524 | void lock_clear_recursive(l) | |
525 | lock_t l; | |
526 | { | |
527 | simple_lock(&l->interlock); | |
528 | if (((thread_t) l->thread) != current_thread()) { | |
529 | panic("lock_clear_recursive: wrong thread"); | |
530 | } | |
531 | if (l->recursion_depth == 0) | |
532 | l->thread = (char *)-1; /* XXX */ | |
533 | simple_unlock(&l->interlock); | |
534 | } |