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Annotation of kernel/kern/lock.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * Copyright (c) 1999 Apple Computer, Inc. All rights reserved.
        !             3:  *
        !             4:  * @APPLE_LICENSE_HEADER_START@
        !             5:  * 
        !             6:  * Portions Copyright (c) 1999 Apple Computer, Inc.  All Rights
        !             7:  * Reserved.  This file contains Original Code and/or Modifications of
        !             8:  * Original Code as defined in and that are subject to the Apple Public
        !             9:  * Source License Version 1.1 (the "License").  You may not use this file
        !            10:  * except in compliance with the License.  Please obtain a copy of the
        !            11:  * License at http://www.apple.com/publicsource and read it before using
        !            12:  * this file.
        !            13:  * 
        !            14:  * The Original Code and all software distributed under the License are
        !            15:  * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
        !            16:  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
        !            17:  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
        !            18:  * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
        !            19:  * License for the specific language governing rights and limitations
        !            20:  * under the License.
        !            21:  * 
        !            22:  * @APPLE_LICENSE_HEADER_END@
        !            23:  */
        !            24: 
        !            25: /* 
        !            26:  * Mach Operating System
        !            27:  * Copyright (c) 1993-1987 Carnegie Mellon University
        !            28:  * All Rights Reserved.
        !            29:  * 
        !            30:  * Permission to use, copy, modify and distribute this software and its
        !            31:  * documentation is hereby granted, provided that both the copyright
        !            32:  * notice and this permission notice appear in all copies of the
        !            33:  * software, derivative works or modified versions, and any portions
        !            34:  * thereof, and that both notices appear in supporting documentation.
        !            35:  * 
        !            36:  * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
        !            37:  * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
        !            38:  * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
        !            39:  * 
        !            40:  * Carnegie Mellon requests users of this software to return to
        !            41:  * 
        !            42:  *  Software Distribution Coordinator  or  [email protected]
        !            43:  *  School of Computer Science
        !            44:  *  Carnegie Mellon University
        !            45:  *  Pittsburgh PA 15213-3890
        !            46:  * 
        !            47:  * any improvements or extensions that they make and grant Carnegie Mellon
        !            48:  * the rights to redistribute these changes.
        !            49:  */
        !            50: /*
        !            51:  *     File:   kern/lock.c
        !            52:  *     Author: Avadis Tevanian, Jr., Michael Wayne Young
        !            53:  *     Date:   1985
        !            54:  *
        !            55:  *     Locking primitives implementation
        !            56:  */
        !            57: 
        !            58: #include <cpus.h>
        !            59: 
        !            60: #include <kern/lock.h>
        !            61: #include <kern/thread.h>
        !            62: #include <kern/sched_prim.h>
        !            63: 
        !            64: 
        !            65: #if (DIAGNOSTIC && defined(__ppc__))
        !            66: void
        !            67: simple_lock(
        !            68:     simple_lock_t       slock)
        !            69: {
        !            70:        real_simple_lock(slock); /* inline in mach/{ppc,i386}/simple_lock.h */
        !            71:        slock->lock_data[1] = (int)(current_thread());
        !            72: }
        !            73: #endif /* DIAGNOSTIC */
        !            74: 
        !            75: #if    NCPUS > 1
        !            76: 
        !            77: /*
        !            78:  *     Module:         lock
        !            79:  *     Function:
        !            80:  *             Provide reader/writer sychronization.
        !            81:  *     Implementation:
        !            82:  *             Simple interlock on a bit.  Readers first interlock,
        !            83:  *             increment the reader count, then let go.  Writers hold
        !            84:  *             the interlock (thus preventing further readers), and
        !            85:  *             wait for already-accepted readers to go away.
        !            86:  */
        !            87: 
        !            88: /*
        !            89:  *     The simple-lock routines are the primitives out of which
        !            90:  *     the lock package is built.  The implementation is left
        !            91:  *     to the machine-dependent code.
        !            92:  */
        !            93: 
        !            94: #ifdef notdef
        !            95: /*
        !            96:  *     A sample implementation of simple locks.
        !            97:  *     assumes:
        !            98:  *             boolean_t test_and_set(boolean_t *)
        !            99:  *                     indivisibly sets the boolean to TRUE
        !           100:  *                     and returns its old value
        !           101:  *             and that setting a boolean to FALSE is indivisible.
        !           102:  */
        !           103: /*
        !           104:  *     simple_lock_init initializes a simple lock.  A simple lock
        !           105:  *     may only be used for exclusive locks.
        !           106:  */
        !           107: 
        !           108: void simple_lock_init(simple_lock_t l)
        !           109: {
        !           110:        *(boolean_t *)l = FALSE;
        !           111: }
        !           112: 
        !           113: void simple_lock(simple_lock_t l)
        !           114: {
        !           115:        while (test_and_set((boolean_t *)l))
        !           116:                continue;
        !           117: }
        !           118: 
        !           119: void simple_unlock(simple_lock_t l)
        !           120: {
        !           121:        *(boolean_t *)l = FALSE;
        !           122: }
        !           123: 
        !           124: boolean_t simple_lock_try(simple_lock_t l)
        !           125: {
        !           126:        return (!test_and_set((boolean_t *)l));
        !           127: }
        !           128: #endif /* notdef */
        !           129: #endif /* NCPUS > 1 */
        !           130: 
        !           131: #if    NCPUS > 1
        !           132: int lock_wait_time = 100;
        !           133: #else  /* NCPUS > 1 */
        !           134: 
        !           135:        /*
        !           136:         *      It is silly to spin on a uni-processor as if we
        !           137:         *      thought something magical would happen to the
        !           138:         *      want_write bit while we are executing.
        !           139:         */
        !           140: int lock_wait_time = 0;
        !           141: #endif /* NCPUS > 1 */
        !           142: 
        !           143: simple_lock_t simple_lock_alloc(void)
        !           144: {
        !           145: #if    MACH_SLOCKS
        !           146:        return (simple_lock_t)kalloc(sizeof(simple_lock_data_t));
        !           147: #else  MACH_SLOCKS
        !           148:        return 0;
        !           149: #endif MACH_SLOCKS
        !           150: }
        !           151: 
        !           152: void simple_lock_free(
        !           153:        simple_lock_t l)
        !           154: {
        !           155: #if    MACH_SLOCKS
        !           156:        kfree(l, sizeof(*l));
        !           157: #endif MACH_SLOCKS
        !           158: }
        !           159: 
        !           160: /*
        !           161:  *     Routine:        lock_alloc
        !           162:  *     Function:
        !           163:  *             Allocate a lock_t data structure.  Used by loadable
        !           164:  *             servers that can't allocate a lock statically.
        !           165:  */
        !           166: lock_t lock_alloc(void)
        !           167: {
        !           168:        return (lock_t)kalloc(sizeof(lock_data_t));
        !           169: }
        !           170: 
        !           171: /*
        !           172:  *     Routine:        lock_free
        !           173:  *     Function:
        !           174:  *             Free a lock allocated by lock_alloc()
        !           175:  */
        !           176: void lock_free(
        !           177:        lock_t  l)
        !           178: {
        !           179:        kfree(l, sizeof(lock_data_t));
        !           180: }
        !           181: 
        !           182: /*
        !           183:  *     Routine:        lock_init
        !           184:  *     Function:
        !           185:  *             Initialize a lock; required before use.
        !           186:  *             Note that clients declare the "struct lock"
        !           187:  *             variables and then initialize them, rather
        !           188:  *             than getting a new one from this module.
        !           189:  */
        !           190: void lock_init(
        !           191:        lock_t          l,
        !           192:        boolean_t       can_sleep)
        !           193: {
        !           194:        bzero((char *)l, sizeof(lock_data_t));
        !           195:        simple_lock_init(&l->interlock);
        !           196:        l->want_write = FALSE;
        !           197:        l->want_upgrade = FALSE;
        !           198:        l->read_count = 0;
        !           199:        l->can_sleep = can_sleep;
        !           200:        l->thread = (struct thread *)-1;        /* XXX */
        !           201:        l->recursion_depth = 0;
        !           202: }
        !           203: 
        !           204: void lock_sleepable(
        !           205:        lock_t          l,
        !           206:        boolean_t       can_sleep)
        !           207: {
        !           208:        simple_lock(&l->interlock);
        !           209:        l->can_sleep = can_sleep;
        !           210:        simple_unlock(&l->interlock);
        !           211: }
        !           212: 
        !           213: 
        !           214: /*
        !           215:  *     Sleep locks.  These use the same data structure and algorithm
        !           216:  *     as the spin locks, but the process sleeps while it is waiting
        !           217:  *     for the lock.  These work on uniprocessor systems.
        !           218:  */
        !           219: 
        !           220: void lock_write(
        !           221:        register lock_t l)
        !           222: {
        !           223:        register int    i;
        !           224: 
        !           225:        simple_lock(&l->interlock);
        !           226: 
        !           227:        if (l->thread == current_thread()) {
        !           228:                /*
        !           229:                 *      Recursive lock.
        !           230:                 */
        !           231:                l->recursion_depth++;
        !           232:                simple_unlock(&l->interlock);
        !           233:                return;
        !           234:        }
        !           235: 
        !           236:        /*
        !           237:         *      Try to acquire the want_write bit.
        !           238:         */
        !           239:        while (l->want_write) {
        !           240:                if ((i = lock_wait_time) > 0) {
        !           241:                        simple_unlock(&l->interlock);
        !           242:                        while (--i > 0 && l->want_write)
        !           243:                                continue;
        !           244:                        simple_lock(&l->interlock);
        !           245:                }
        !           246: 
        !           247:                if (l->can_sleep && l->want_write) {
        !           248:                        l->waiting = TRUE;
        !           249:                        thread_sleep(l,
        !           250:                                simple_lock_addr(l->interlock), FALSE);
        !           251:                        simple_lock(&l->interlock);
        !           252:                }
        !           253:        }
        !           254:        l->want_write = TRUE;
        !           255: 
        !           256:        /* Wait for readers (and upgrades) to finish */
        !           257: 
        !           258:        while ((l->read_count != 0) || l->want_upgrade) {
        !           259:                if ((i = lock_wait_time) > 0) {
        !           260:                        simple_unlock(&l->interlock);
        !           261:                        while (--i > 0 && (l->read_count != 0 ||
        !           262:                                        l->want_upgrade))
        !           263:                                continue;
        !           264:                        simple_lock(&l->interlock);
        !           265:                }
        !           266: 
        !           267:                if (l->can_sleep && (l->read_count != 0 || l->want_upgrade)) {
        !           268:                        l->waiting = TRUE;
        !           269:                        thread_sleep(l,
        !           270:                                simple_lock_addr(l->interlock), FALSE);
        !           271:                        simple_lock(&l->interlock);
        !           272:                }
        !           273:        }
        !           274:        simple_unlock(&l->interlock);
        !           275: }
        !           276: 
        !           277: void lock_done(
        !           278:        register lock_t l)
        !           279: {
        !           280:        simple_lock(&l->interlock);
        !           281: 
        !           282:        if (l->read_count != 0)
        !           283:                l->read_count--;
        !           284:        else
        !           285:        if (l->recursion_depth != 0)
        !           286:                l->recursion_depth--;
        !           287:        else
        !           288:        if (l->want_upgrade)
        !           289:                l->want_upgrade = FALSE;
        !           290:        else
        !           291:                l->want_write = FALSE;
        !           292: 
        !           293:        /*
        !           294:         *      There is no reason to wakeup a waiting thread
        !           295:         *      if the read-count is non-zero.  Consider:
        !           296:         *              we must be dropping a read lock
        !           297:         *              threads are waiting only if one wants a write lock
        !           298:         *              if there are still readers, they can't proceed
        !           299:         */
        !           300: 
        !           301:        if (l->waiting && (l->read_count == 0)) {
        !           302:                l->waiting = FALSE;
        !           303:                thread_wakeup(l);
        !           304:        }
        !           305: 
        !           306:        simple_unlock(&l->interlock);
        !           307: }
        !           308: 
        !           309: void lock_read(
        !           310:        register lock_t l)
        !           311: {
        !           312:        register int    i;
        !           313: 
        !           314:        simple_lock(&l->interlock);
        !           315: 
        !           316:        if (l->thread == current_thread()) {
        !           317:                /*
        !           318:                 *      Recursive lock.
        !           319:                 */
        !           320:                l->read_count++;
        !           321:                simple_unlock(&l->interlock);
        !           322:                return;
        !           323:        }
        !           324: 
        !           325:        while (l->want_write || l->want_upgrade) {
        !           326:                if ((i = lock_wait_time) > 0) {
        !           327:                        simple_unlock(&l->interlock);
        !           328:                        while (--i > 0 && (l->want_write || l->want_upgrade))
        !           329:                                continue;
        !           330:                        simple_lock(&l->interlock);
        !           331:                }
        !           332: 
        !           333:                if (l->can_sleep && (l->want_write || l->want_upgrade)) {
        !           334:                        l->waiting = TRUE;
        !           335:                        thread_sleep(l,
        !           336:                                simple_lock_addr(l->interlock), FALSE);
        !           337:                        simple_lock(&l->interlock);
        !           338:                }
        !           339:        }
        !           340: 
        !           341:        l->read_count++;
        !           342:        simple_unlock(&l->interlock);
        !           343: }
        !           344: 
        !           345: /*
        !           346:  *     Routine:        lock_read_to_write
        !           347:  *     Function:
        !           348:  *             Improves a read-only lock to one with
        !           349:  *             write permission.  If another reader has
        !           350:  *             already requested an upgrade to a write lock,
        !           351:  *             no lock is held upon return.
        !           352:  *
        !           353:  *             Returns TRUE if the upgrade *failed*.
        !           354:  */
        !           355: boolean_t lock_read_to_write(
        !           356:        register lock_t l)
        !           357: {
        !           358:        register int    i;
        !           359: 
        !           360:        simple_lock(&l->interlock);
        !           361: 
        !           362:        l->read_count--;
        !           363: 
        !           364:        if (l->thread == current_thread()) {
        !           365:                /*
        !           366:                 *      Recursive lock.
        !           367:                 */
        !           368:                l->recursion_depth++;
        !           369:                simple_unlock(&l->interlock);
        !           370:                return(FALSE);
        !           371:        }
        !           372: 
        !           373:        if (l->want_upgrade) {
        !           374:                /*
        !           375:                 *      Someone else has requested upgrade.
        !           376:                 *      Since we've released a read lock, wake
        !           377:                 *      him up.
        !           378:                 */
        !           379:                if (l->waiting && (l->read_count == 0)) {
        !           380:                        l->waiting = FALSE;
        !           381:                        thread_wakeup(l);
        !           382:                }
        !           383: 
        !           384:                simple_unlock(&l->interlock);
        !           385:                return TRUE;
        !           386:        }
        !           387: 
        !           388:        l->want_upgrade = TRUE;
        !           389: 
        !           390:        while (l->read_count != 0) {
        !           391:                if ((i = lock_wait_time) > 0) {
        !           392:                        simple_unlock(&l->interlock);
        !           393:                        while (--i > 0 && l->read_count != 0)
        !           394:                                continue;
        !           395:                        simple_lock(&l->interlock);
        !           396:                }
        !           397: 
        !           398:                if (l->can_sleep && l->read_count != 0) {
        !           399:                        l->waiting = TRUE;
        !           400:                        thread_sleep(l,
        !           401:                                simple_lock_addr(l->interlock), FALSE);
        !           402:                        simple_lock(&l->interlock);
        !           403:                }
        !           404:        }
        !           405: 
        !           406:        simple_unlock(&l->interlock);
        !           407:        return FALSE;
        !           408: }
        !           409: 
        !           410: void lock_write_to_read(
        !           411:        register lock_t l)
        !           412: {
        !           413:        simple_lock(&l->interlock);
        !           414: 
        !           415:        l->read_count++;
        !           416:        if (l->recursion_depth != 0)
        !           417:                l->recursion_depth--;
        !           418:        else
        !           419:        if (l->want_upgrade)
        !           420:                l->want_upgrade = FALSE;
        !           421:        else
        !           422:                l->want_write = FALSE;
        !           423: 
        !           424:        if (l->waiting) {
        !           425:                l->waiting = FALSE;
        !           426:                thread_wakeup(l);
        !           427:        }
        !           428: 
        !           429:        simple_unlock(&l->interlock);
        !           430: }
        !           431: 
        !           432: 
        !           433: /*
        !           434:  *     Routine:        lock_try_write
        !           435:  *     Function:
        !           436:  *             Tries to get a write lock.
        !           437:  *
        !           438:  *             Returns FALSE if the lock is not held on return.
        !           439:  */
        !           440: 
        !           441: boolean_t lock_try_write(
        !           442:        register lock_t l)
        !           443: {
        !           444:        simple_lock(&l->interlock);
        !           445: 
        !           446:        if (l->thread == current_thread()) {
        !           447:                /*
        !           448:                 *      Recursive lock
        !           449:                 */
        !           450:                l->recursion_depth++;
        !           451:                simple_unlock(&l->interlock);
        !           452:                return TRUE;
        !           453:        }
        !           454: 
        !           455:        if (l->want_write || l->want_upgrade || l->read_count) {
        !           456:                /*
        !           457:                 *      Can't get lock.
        !           458:                 */
        !           459:                simple_unlock(&l->interlock);
        !           460:                return FALSE;
        !           461:        }
        !           462: 
        !           463:        /*
        !           464:         *      Have lock.
        !           465:         */
        !           466: 
        !           467:        l->want_write = TRUE;
        !           468:        simple_unlock(&l->interlock);
        !           469:        return TRUE;
        !           470: }
        !           471: 
        !           472: /*
        !           473:  *     Routine:        lock_try_read
        !           474:  *     Function:
        !           475:  *             Tries to get a read lock.
        !           476:  *
        !           477:  *             Returns FALSE if the lock is not held on return.
        !           478:  */
        !           479: 
        !           480: boolean_t lock_try_read(
        !           481:        register lock_t l)
        !           482: {
        !           483:        simple_lock(&l->interlock);
        !           484: 
        !           485:        if (l->thread == current_thread()) {
        !           486:                /*
        !           487:                 *      Recursive lock
        !           488:                 */
        !           489:                l->read_count++;
        !           490:                simple_unlock(&l->interlock);
        !           491:                return TRUE;
        !           492:        }
        !           493: 
        !           494:        if (l->want_write || l->want_upgrade) {
        !           495:                simple_unlock(&l->interlock);
        !           496:                return FALSE;
        !           497:        }
        !           498: 
        !           499:        l->read_count++;
        !           500:        simple_unlock(&l->interlock);
        !           501:        return TRUE;
        !           502: }
        !           503: 
        !           504: /*
        !           505:  *     Routine:        lock_try_read_to_write
        !           506:  *     Function:
        !           507:  *             Improves a read-only lock to one with
        !           508:  *             write permission.  If another reader has
        !           509:  *             already requested an upgrade to a write lock,
        !           510:  *             the read lock is still held upon return.
        !           511:  *
        !           512:  *             Returns FALSE if the upgrade *failed*.
        !           513:  */
        !           514: boolean_t lock_try_read_to_write(
        !           515:        register lock_t l)
        !           516: {
        !           517:        simple_lock(&l->interlock);
        !           518: 
        !           519:        if (l->thread == current_thread()) {
        !           520:                /*
        !           521:                 *      Recursive lock
        !           522:                 */
        !           523:                l->read_count--;
        !           524:                l->recursion_depth++;
        !           525:                simple_unlock(&l->interlock);
        !           526:                return TRUE;
        !           527:        }
        !           528: 
        !           529:        if (l->want_upgrade) {
        !           530:                simple_unlock(&l->interlock);
        !           531:                return FALSE;
        !           532:        }
        !           533:        l->want_upgrade = TRUE;
        !           534:        l->read_count--;
        !           535: 
        !           536:        while (l->read_count != 0) {
        !           537:                l->waiting = TRUE;
        !           538:                thread_sleep(l,
        !           539:                        simple_lock_addr(l->interlock), FALSE);
        !           540:                simple_lock(&l->interlock);
        !           541:        }
        !           542: 
        !           543:        simple_unlock(&l->interlock);
        !           544:        return TRUE;
        !           545: }
        !           546: 
        !           547: /*
        !           548:  *     Allow a process that has a lock for write to acquire it
        !           549:  *     recursively (for read, write, or update).
        !           550:  */
        !           551: void lock_set_recursive(
        !           552:        lock_t          l)
        !           553: {
        !           554:        simple_lock(&l->interlock);
        !           555:        if (!l->want_write) {
        !           556:                panic("lock_set_recursive: don't have write lock");
        !           557:        }
        !           558:        l->thread = current_thread();
        !           559:        simple_unlock(&l->interlock);
        !           560: }
        !           561: 
        !           562: /*
        !           563:  *     Prevent a lock from being re-acquired.
        !           564:  */
        !           565: void lock_clear_recursive(
        !           566:        lock_t          l)
        !           567: {
        !           568:        simple_lock(&l->interlock);
        !           569:        if (l->thread != current_thread()) {
        !           570:                panic("lock_clear_recursive: wrong thread");
        !           571:        }
        !           572:        if (l->recursion_depth == 0)
        !           573:                l->thread = (struct thread *)-1;        /* XXX */
        !           574:        simple_unlock(&l->interlock);
        !           575: }

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