/*-
 * 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);
}