diff options
Diffstat (limited to 'db2/mutex/mutex.c')
| -rw-r--r-- | db2/mutex/mutex.c | 280 |
1 files changed, 280 insertions, 0 deletions
diff --git a/db2/mutex/mutex.c b/db2/mutex/mutex.c new file mode 100644 index 0000000000..b23f738ad7 --- /dev/null +++ b/db2/mutex/mutex.c @@ -0,0 +1,280 @@ +/*- + * See the file LICENSE for redistribution information. + * + * Copyright (c) 1996, 1997 + * Sleepycat Software. All rights reserved. + */ + +#include "config.h" + +#ifndef lint +static const char sccsid[] = "@(#)mutex.c 10.22 (Sleepycat) 8/21/97"; +#endif /* not lint */ + +#ifndef NO_SYSTEM_INCLUDES +#include <sys/types.h> + +#include <errno.h> +#include <fcntl.h> +#include <stdio.h> +#include <stdlib.h> +#include <string.h> +#include <unistd.h> +#endif + +#include "db_int.h" +#include "common_ext.h" + +#ifdef HAVE_SPINLOCKS + +#ifdef HAVE_FUNC_AIX +#define TSL_INIT(x) +#define TSL_SET(x) (!_check_lock(x, 0, 1)) +#define TSL_UNSET(x) _clear_lock(x, 0) +#endif + +#ifdef HAVE_ASSEM_MC68020_GCC +#include "68020.gcc" +#endif + +#if defined(HAVE_FUNC_MSEM) +/* + * XXX + * Should we not use MSEM_IF_NOWAIT and let the system block for us? + * I've no idea if this will block all threads in the process or not. + */ +#define TSL_INIT(x) msem_init(x, MSEM_UNLOCKED) +#define TSL_SET(x) (!msem_lock(x, MSEM_IF_NOWAIT)) +#define TSL_UNSET(x) msem_unlock(x, 0) +#endif + +#ifdef HAVE_FUNC_SGI +#define TSL_INIT(x) init_lock(x) +#define TSL_SET(x) (!acquire_lock(x)) +#define TSL_UNSET(x) release_lock(x) +#endif + +#ifdef HAVE_FUNC_SOLARIS +/* + * Semaphore calls don't work on Solaris 5.5. + * + * #define TSL_INIT(x) sema_init(x, 1, USYNC_PROCESS, NULL) + * #define TSL_SET(x) (sema_wait(x) == 0) + * #define TSL_UNSET(x) sema_post(x) + */ +#define TSL_INIT(x) +#define TSL_SET(x) (_lock_try(x)) +#define TSL_UNSET(x) _lock_clear(x) +#endif + +#ifdef HAVE_ASSEM_SPARC_GCC +#include "sparc.gcc" +#endif + +#ifdef HAVE_ASSEM_UTS4_CC +#define TSL_INIT(x) +#define TSL_SET(x) (!uts_lock(x, 1)) +#define TSL_UNSET(x) (*(x) = 0) +#endif + +#ifdef HAVE_ASSEM_X86_GCC +#include "x86.gcc" +#endif + +#if defined(_WIN32) +/* DBDB this needs to be byte-aligned!! */ +#define TSL_INIT(tsl) +#define TSL_SET(tsl) (!InterlockedExchange((PLONG)tsl, 1)) +#define TSL_UNSET(tsl) (*(tsl) = 0) +#endif + +#ifdef macintosh +/* Mac spinlocks are simple because we cannot possibly be preempted. */ +#define TSL_INIT(tsl) +#define TSL_SET(tsl) (*(tsl) = 1) +#define TSL_UNSET(tsl) (*(tsl) = 0) +#endif + +#endif /* HAVE_SPINLOCKS */ + +#ifdef MORE_THAN_ONE_PROCESSOR +#define TSL_DEFAULT_SPINS 5 /* Default spins before block. */ +#else +#define TSL_DEFAULT_SPINS 1 /* Default spins before block. */ +#endif + +/* + * __db_mutex_init -- + * Initialize a DB mutex structure. + * + * PUBLIC: void __db_mutex_init __P((db_mutex_t *, off_t)); + */ +void +__db_mutex_init(mp, off) + db_mutex_t *mp; + off_t off; +{ +#ifdef DEBUG + if ((ALIGNTYPE)mp & (MUTEX_ALIGNMENT - 1)) { + (void)fprintf(stderr, + "MUTEX ERROR: mutex NOT %d-byte aligned!\n", + MUTEX_ALIGNMENT); + abort(); + } +#endif + memset(mp, 0, sizeof(db_mutex_t)); + +#ifdef HAVE_SPINLOCKS + TSL_INIT(&mp->tsl_resource); +#else + mp->off = off; +#endif +} + +#define MS(n) ((n) * 1000) /* Milliseconds to micro-seconds. */ +#define SECOND (MS(1000)) /* A second's worth of micro-seconds. */ + +/* + * __db_mutex_lock + * Lock on a mutex, logically blocking if necessary. + * + * PUBLIC: int __db_mutex_lock __P((db_mutex_t *, int, int (*)(void))); + */ +int +__db_mutex_lock(mp, fd, yield) + db_mutex_t *mp; + int fd; + int (*yield) __P((void)); +{ + u_long usecs; + +#ifdef HAVE_SPINLOCKS + int nspins; + + for (usecs = MS(10);;) { + /* + * Try and acquire the uncontested resource lock for + * TSL_DEFAULT_SPINS. + */ + for (nspins = TSL_DEFAULT_SPINS; nspins > 0; --nspins) + if (TSL_SET(&mp->tsl_resource)) { +#ifdef DEBUG + if (mp->pid != 0) { + (void)fprintf(stderr, + "MUTEX ERROR: __db_mutex_lock: lock currently locked\n"); + abort(); + } + mp->pid = getpid(); +#endif +#ifdef MUTEX_STATISTICS + if (usecs == MS(10)) + ++mp->mutex_set_nowait; + else + ++mp->mutex_set_wait; +#endif + return (0); + } + + /* Yield the processor; wait 10ms initially, up to 1 second. */ + if (yield == NULL || yield() != 0) { + (void)__db_sleep(0, usecs); + if ((usecs <<= 1) > SECOND) + usecs = SECOND; + } + } + /* NOTREACHED */ + +#else /* !HAVE_SPINLOCKS */ + struct flock k_lock; + pid_t mypid; + int locked; + + /* Initialize the lock. */ + k_lock.l_whence = SEEK_SET; + k_lock.l_start = mp->off; + k_lock.l_len = 1; + + for (locked = 0, mypid = getpid();;) { + /* + * Wait for the lock to become available; wait 10ms initially, + * up to 1 second. + */ + for (usecs = MS(10); mp->pid != 0;) + if (yield == NULL || yield() != 0) { + (void)__db_sleep(0, usecs); + if ((usecs <<= 1) > SECOND) + usecs = SECOND; + } + + /* Acquire an exclusive kernel lock. */ + k_lock.l_type = F_WRLCK; + if (fcntl(fd, F_SETLKW, &k_lock)) + return (1); + + /* If the resource tsl is still available, it's ours. */ + if (mp->pid == 0) { + locked = 1; + mp->pid = mypid; + } + + /* Release the kernel lock. */ + k_lock.l_type = F_UNLCK; + if (fcntl(fd, F_SETLK, &k_lock)) + return (1); + + /* + * If we got the resource tsl we're done. + * + * !!! + * We can't check to see if the lock is ours, because we may + * be trying to block ourselves in the lock manager, and so + * the holder of the lock that's preventing us from getting + * the lock may be us! (Seriously.) + */ + if (locked) + break; + } + +#ifdef MUTEX_STATISTICS + ++mp->mutex_set_wait; +#endif + return (0); +#endif /* !HAVE_SPINLOCKS */ +} + +/* + * __db_mutex_unlock -- + * Release a lock. + * + * PUBLIC: int __db_mutex_unlock __P((db_mutex_t *, int)); + */ +int +__db_mutex_unlock(mp, fd) + db_mutex_t *mp; + int fd; +{ +#ifdef DEBUG + if (mp->pid == 0) { + (void)fprintf(stderr, + "MUTEX ERROR: __db_mutex_unlock: lock already unlocked\n"); + abort(); + } +#endif + +#ifdef HAVE_SPINLOCKS +#ifdef DEBUG + mp->pid = 0; +#endif + + /* Release the resource tsl. */ + TSL_UNSET(&mp->tsl_resource); +#else + /* + * Release the resource tsl. We don't have to acquire any locks + * because processes trying to acquire the lock are checking for + * a pid of 0, not a specific value. + */ + mp->pid = 0; +#endif + return (0); +} |