db/mutex/mutex.c

	mutex.c revision 7c478bd95313f5f23a4c958a745db2134aa03244
/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996, 1997, 1998
 *  Sleepycat Software.  All rights reserved.
 */

#include "config.h"

#ifndef lint
static const char sccsid[] = "@(#)mutex.c   10.52 (Sleepycat) 11/8/98";
#endif /* not lint */

#ifndef NO_SYSTEM_INCLUDES
#include <sys/types.h>

#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#endif

#include "db_int.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)
/*
 * !!!
 * Do not remove the MSEM_IF_NOWAIT flag.  The problem is that if a single
 * process makes two msem_lock() calls in a row, the second one returns an
 * error.  We depend on the fact that we can lock against ourselves in the
 * locking subsystem, where we set up a mutex so that we can block ourselves.
 * Tested on OSF1 v4.0.
 */
#define TSL_INIT(x) (msem_init(x, MSEM_UNLOCKED) == NULL)
#define TSL_INIT_ERROR  1
#define TSL_SET(x)  (!msem_lock(x, MSEM_IF_NOWAIT))
#define TSL_UNSET(x)    msem_unlock(x, 0)
#endif

#ifdef HAVE_FUNC_RELIANT
#define TSL_INIT(x) initspin(x, 1)
#define TSL_SET(x)  (cspinlock(x) == 0)
#define TSL_UNSET(x)    spinunlock(x)
#endif

#ifdef HAVE_FUNC_SGI
#define TSL_INIT(x) (init_lock(x) != 0)
#define TSL_INIT_ERROR  1
#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) != 0)
 * #define  TSL_INIT_ERROR  1
 * #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_FUNC_VMS
#include <builtins.h>
#ifdef __ALPHA
#define TSL_SET(tsl)    (!__TESTBITSSI(tsl, 0))
#else /* __VAX */
#define TSL_SET(tsl)    (!(int)_BBSSI(0, tsl))
#endif
#define TSL_UNSET(tsl)  (*(tsl) = 0)
#define TSL_INIT(tsl)   TSL_UNSET(tsl)
#endif

#ifdef HAVE_ASSEM_PARISC_GCC
#include "parisc.gcc"
#endif

#ifdef HAVE_ASSEM_SCO_CC
#include "sco.cc"
#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

#ifdef WIN16
/* Win16 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

#if defined(_WIN32)
/*
 * XXX
 * 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

#endif /* HAVE_SPINLOCKS */

/*
 * __db_mutex_init --
 *  Initialize a DB mutex structure.
 *
 * PUBLIC: int __db_mutex_init __P((db_mutex_t *, u_int32_t));
 */
int
__db_mutex_init(mp, off)
    db_mutex_t *mp;
    u_int32_t off;
{
#ifdef DIAGNOSTIC
    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
    COMPQUIET(off, 0);

#ifdef TSL_INIT_ERROR
    if (TSL_INIT(&mp->tsl_resource))
        return (errno);
#else
    TSL_INIT(&mp->tsl_resource);
#endif
    mp->spins = __os_spin();
#else
    mp->off = off;
#endif
    return (0);
}

#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
__db_mutex_lock(mp, fd)
    db_mutex_t *mp;
    int fd;
{
    u_long usecs;
#ifdef HAVE_SPINLOCKS
    int nspins;
#else
    struct flock k_lock;
    pid_t mypid;
    int locked;
#endif

    if (!DB_GLOBAL(db_mutexlocks))
        return (0);

#ifdef HAVE_SPINLOCKS
    COMPQUIET(fd, 0);

    for (usecs = MS(1);;) {
        /* Try and acquire the uncontested resource lock for N spins. */
        for (nspins = mp->spins; nspins > 0; --nspins)
            if (TSL_SET(&mp->tsl_resource)) {
#ifdef DIAGNOSTIC
                if (mp->pid != 0) {
                    (void)fprintf(stderr,
            "MUTEX ERROR: __db_mutex_lock: lock currently locked\n");
                    abort();
                }
                mp->pid = getpid();
#endif
                if (usecs == MS(1))
                    ++mp->mutex_set_nowait;
                else
                    ++mp->mutex_set_wait;
                return (0);
            }

        /* Yield the processor; wait 1ms initially, up to 1 second. */
        __os_yield(usecs);
        if ((usecs <<= 1) > SECOND)
            usecs = SECOND;
    }
    /* NOTREACHED */

#else /* !HAVE_SPINLOCKS */

    /* 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 1ms initially,
         * up to 1 second.
         */
        for (usecs = MS(1); mp->pid != 0;) {
            __os_yield(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 (errno);

        /* 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 (errno);

        /*
         * 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;
    }
    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;
{
    if (!DB_GLOBAL(db_mutexlocks))
        return (0);

#ifdef DIAGNOSTIC
    if (mp->pid == 0) {
        (void)fprintf(stderr,
        "MUTEX ERROR: __db_mutex_unlock: lock already unlocked\n");
        abort();
    }
#endif

#ifdef HAVE_SPINLOCKS
    COMPQUIET(fd, 0);

#ifdef DIAGNOSTIC
    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);
}