315 lines
6.4 KiB
C
315 lines
6.4 KiB
C
/*-
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* See the file LICENSE for redistribution information.
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*
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* Copyright (c) 1996, 1997, 1998
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* Sleepycat Software. All rights reserved.
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*/
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#include "config.h"
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#ifndef lint
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static const char sccsid[] = "@(#)mutex.c 10.52 (Sleepycat) 11/8/98";
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#endif /* not lint */
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#ifndef NO_SYSTEM_INCLUDES
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#include <sys/types.h>
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#include <errno.h>
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#include <fcntl.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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#endif
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#include "db_int.h"
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#ifdef HAVE_SPINLOCKS
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#ifdef HAVE_FUNC_AIX
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#define TSL_INIT(x)
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#define TSL_SET(x) (!_check_lock(x, 0, 1))
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#define TSL_UNSET(x) _clear_lock(x, 0)
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#endif
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#ifdef HAVE_ASSEM_MC68020_GCC
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#include "68020.gcc"
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#endif
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#if defined(HAVE_FUNC_MSEM)
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/*
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* !!!
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* Do not remove the MSEM_IF_NOWAIT flag. The problem is that if a single
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* process makes two msem_lock() calls in a row, the second one returns an
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* error. We depend on the fact that we can lock against ourselves in the
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* locking subsystem, where we set up a mutex so that we can block ourselves.
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* Tested on OSF1 v4.0.
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*/
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#define TSL_INIT(x) (msem_init(x, MSEM_UNLOCKED) == NULL)
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#define TSL_INIT_ERROR 1
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#define TSL_SET(x) (!msem_lock(x, MSEM_IF_NOWAIT))
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#define TSL_UNSET(x) msem_unlock(x, 0)
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#endif
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#ifdef HAVE_FUNC_RELIANT
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#define TSL_INIT(x) initspin(x, 1)
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#define TSL_SET(x) (cspinlock(x) == 0)
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#define TSL_UNSET(x) spinunlock(x)
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#endif
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#ifdef HAVE_FUNC_SGI
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#define TSL_INIT(x) (init_lock(x) != 0)
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#define TSL_INIT_ERROR 1
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#define TSL_SET(x) (!acquire_lock(x))
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#define TSL_UNSET(x) release_lock(x)
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#endif
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#ifdef HAVE_FUNC_SOLARIS
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/*
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* Semaphore calls don't work on Solaris 5.5.
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*
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* #define TSL_INIT(x) (sema_init(x, 1, USYNC_PROCESS, NULL) != 0)
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* #define TSL_INIT_ERROR 1
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* #define TSL_SET(x) (sema_wait(x) == 0)
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* #define TSL_UNSET(x) sema_post(x)
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*/
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#define TSL_INIT(x)
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#define TSL_SET(x) (_lock_try(x))
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#define TSL_UNSET(x) _lock_clear(x)
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#endif
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#ifdef HAVE_FUNC_VMS
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#include <builtins.h>
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#ifdef __ALPHA
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#define TSL_SET(tsl) (!__TESTBITSSI(tsl, 0))
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#else /* __VAX */
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#define TSL_SET(tsl) (!(int)_BBSSI(0, tsl))
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#endif
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#define TSL_UNSET(tsl) (*(tsl) = 0)
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#define TSL_INIT(tsl) TSL_UNSET(tsl)
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#endif
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#ifdef HAVE_ASSEM_PARISC_GCC
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#include "parisc.gcc"
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#endif
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#ifdef HAVE_ASSEM_SCO_CC
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#include "sco.cc"
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#endif
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#ifdef HAVE_ASSEM_SPARC_GCC
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#include "sparc.gcc"
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#endif
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#ifdef HAVE_ASSEM_UTS4_CC
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#define TSL_INIT(x)
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#define TSL_SET(x) (!uts_lock(x, 1))
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#define TSL_UNSET(x) (*(x) = 0)
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#endif
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#ifdef HAVE_ASSEM_X86_GCC
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#include "x86.gcc"
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#endif
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#ifdef WIN16
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/* Win16 spinlocks are simple because we cannot possibly be preempted. */
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#define TSL_INIT(tsl)
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#define TSL_SET(tsl) (*(tsl) = 1)
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#define TSL_UNSET(tsl) (*(tsl) = 0)
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#endif
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#if defined(_WIN32)
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/*
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* XXX
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* DBDB this needs to be byte-aligned!!
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*/
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#define TSL_INIT(tsl)
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#define TSL_SET(tsl) (!InterlockedExchange((PLONG)tsl, 1))
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#define TSL_UNSET(tsl) (*(tsl) = 0)
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#endif
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#endif /* HAVE_SPINLOCKS */
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/*
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* __db_mutex_init --
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* Initialize a DB mutex structure.
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*
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* PUBLIC: int __db_mutex_init __P((db_mutex_t *, u_int32_t));
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*/
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int
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__db_mutex_init(mp, off)
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db_mutex_t *mp;
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u_int32_t off;
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{
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#ifdef DIAGNOSTIC
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if ((ALIGNTYPE)mp & (MUTEX_ALIGNMENT - 1)) {
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(void)fprintf(stderr,
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"MUTEX ERROR: mutex NOT %d-byte aligned!\n",
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MUTEX_ALIGNMENT);
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abort();
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}
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#endif
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memset(mp, 0, sizeof(db_mutex_t));
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#ifdef HAVE_SPINLOCKS
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COMPQUIET(off, 0);
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#ifdef TSL_INIT_ERROR
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if (TSL_INIT(&mp->tsl_resource))
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return (errno);
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#else
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TSL_INIT(&mp->tsl_resource);
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#endif
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mp->spins = __os_spin();
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#else
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mp->off = off;
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#endif
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return (0);
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}
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#define MS(n) ((n) * 1000) /* Milliseconds to micro-seconds. */
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#define SECOND (MS(1000)) /* A second's worth of micro-seconds. */
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/*
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* __db_mutex_lock
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* Lock on a mutex, logically blocking if necessary.
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*
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* PUBLIC: int __db_mutex_lock __P((db_mutex_t *, int));
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*/
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int
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__db_mutex_lock(mp, fd)
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db_mutex_t *mp;
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int fd;
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{
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u_long usecs;
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#ifdef HAVE_SPINLOCKS
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int nspins;
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#else
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struct flock k_lock;
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pid_t mypid;
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int locked;
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#endif
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if (!DB_GLOBAL(db_mutexlocks))
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return (0);
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#ifdef HAVE_SPINLOCKS
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COMPQUIET(fd, 0);
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for (usecs = MS(1);;) {
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/* Try and acquire the uncontested resource lock for N spins. */
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for (nspins = mp->spins; nspins > 0; --nspins)
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if (TSL_SET(&mp->tsl_resource)) {
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#ifdef DIAGNOSTIC
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if (mp->pid != 0) {
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(void)fprintf(stderr,
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"MUTEX ERROR: __db_mutex_lock: lock currently locked\n");
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abort();
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}
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mp->pid = getpid();
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#endif
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if (usecs == MS(1))
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++mp->mutex_set_nowait;
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else
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++mp->mutex_set_wait;
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return (0);
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}
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/* Yield the processor; wait 1ms initially, up to 1 second. */
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__os_yield(usecs);
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if ((usecs <<= 1) > SECOND)
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usecs = SECOND;
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}
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/* NOTREACHED */
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#else /* !HAVE_SPINLOCKS */
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/* Initialize the lock. */
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k_lock.l_whence = SEEK_SET;
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k_lock.l_start = mp->off;
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k_lock.l_len = 1;
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for (locked = 0, mypid = getpid();;) {
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/*
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* Wait for the lock to become available; wait 1ms initially,
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* up to 1 second.
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*/
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for (usecs = MS(1); mp->pid != 0;) {
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__os_yield(usecs);
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if ((usecs <<= 1) > SECOND)
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usecs = SECOND;
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}
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/* Acquire an exclusive kernel lock. */
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k_lock.l_type = F_WRLCK;
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if (fcntl(fd, F_SETLKW, &k_lock))
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return (errno);
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/* If the resource tsl is still available, it's ours. */
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if (mp->pid == 0) {
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locked = 1;
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mp->pid = mypid;
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}
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/* Release the kernel lock. */
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k_lock.l_type = F_UNLCK;
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if (fcntl(fd, F_SETLK, &k_lock))
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return (errno);
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/*
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* If we got the resource tsl we're done.
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*
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* !!!
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* We can't check to see if the lock is ours, because we may
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* be trying to block ourselves in the lock manager, and so
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* the holder of the lock that's preventing us from getting
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* the lock may be us! (Seriously.)
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*/
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if (locked)
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break;
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}
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return (0);
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#endif /* !HAVE_SPINLOCKS */
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}
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/*
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* __db_mutex_unlock --
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* Release a lock.
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*
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* PUBLIC: int __db_mutex_unlock __P((db_mutex_t *, int));
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*/
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int
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__db_mutex_unlock(mp, fd)
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db_mutex_t *mp;
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int fd;
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{
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if (!DB_GLOBAL(db_mutexlocks))
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return (0);
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#ifdef DIAGNOSTIC
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if (mp->pid == 0) {
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(void)fprintf(stderr,
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"MUTEX ERROR: __db_mutex_unlock: lock already unlocked\n");
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abort();
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}
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#endif
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#ifdef HAVE_SPINLOCKS
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COMPQUIET(fd, 0);
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#ifdef DIAGNOSTIC
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mp->pid = 0;
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#endif
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/* Release the resource tsl. */
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TSL_UNSET(&mp->tsl_resource);
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#else
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/*
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* Release the resource tsl. We don't have to acquire any locks
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* because processes trying to acquire the lock are checking for
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* a pid of 0, not a specific value.
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*/
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mp->pid = 0;
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#endif
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return (0);
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}
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