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/*-
* See the file LICENSE for redistribution information.
*
* Copyright (c) 1996,2007 Oracle. All rights reserved.
*
* $Id: mut_fcntl.c,v 12.23 2007/05/17 15:15:45 bostic Exp $
*/
#include "db_config.h"
#include "db_int.h"
#include "dbinc/mutex_int.h"
/*
* __db_fcntl_mutex_init --
* Initialize a fcntl mutex.
*
* PUBLIC: int __db_fcntl_mutex_init __P((DB_ENV *, db_mutex_t, u_int32_t));
*/
int
__db_fcntl_mutex_init(dbenv, mutex, flags)
DB_ENV *dbenv;
db_mutex_t mutex;
u_int32_t flags;
{
COMPQUIET(dbenv, NULL);
COMPQUIET(mutex, MUTEX_INVALID);
COMPQUIET(flags, 0);
return (0);
}
/*
* __db_fcntl_mutex_lock
* Lock on a mutex, blocking if necessary.
*
* PUBLIC: int __db_fcntl_mutex_lock __P((DB_ENV *, db_mutex_t));
*/
int
__db_fcntl_mutex_lock(dbenv, mutex)
DB_ENV *dbenv;
db_mutex_t mutex;
{
DB_MUTEX *mutexp;
DB_MUTEXMGR *mtxmgr;
DB_MUTEXREGION *mtxregion;
struct flock k_lock;
int locked, ms, ret;
if (!MUTEX_ON(dbenv) || F_ISSET(dbenv, DB_ENV_NOLOCKING))
return (0);
mtxmgr = dbenv->mutex_handle;
mtxregion = mtxmgr->reginfo.primary;
mutexp = MUTEXP_SET(mutex);
#ifdef HAVE_STATISTICS
if (F_ISSET(mutexp, DB_MUTEX_LOCKED))
++mutexp->mutex_set_wait;
else
++mutexp->mutex_set_nowait;
#endif
/* Initialize the lock. */
k_lock.l_whence = SEEK_SET;
k_lock.l_start = mutex;
k_lock.l_len = 1;
for (locked = 0;;) {
/*
* Wait for the lock to become available; wait 1ms initially,
* up to 1 second.
*/
for (ms = 1; F_ISSET(mutexp, DB_MUTEX_LOCKED);) {
__os_sleep(NULL, 0, ms * US_PER_MS);
if ((ms <<= 1) > MS_PER_SEC)
ms = MS_PER_SEC;
}
/* Acquire an exclusive kernel lock. */
k_lock.l_type = F_WRLCK;
if (fcntl(dbenv->lockfhp->fd, F_SETLKW, &k_lock))
goto err;
/* If the resource is still available, it's ours. */
if (!F_ISSET(mutexp, DB_MUTEX_LOCKED)) {
locked = 1;
F_SET(mutexp, DB_MUTEX_LOCKED);
dbenv->thread_id(dbenv, &mutexp->pid, &mutexp->tid);
CHECK_MTX_THREAD(dbenv, mutexp);
}
/* Release the kernel lock. */
k_lock.l_type = F_UNLCK;
if (fcntl(dbenv->lockfhp->fd, F_SETLK, &k_lock))
goto err;
/*
* If we got the resource lock 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 DIAGNOSTIC
/*
* We want to switch threads as often as possible. Yield every time
* we get a mutex to ensure contention.
*/
if (F_ISSET(dbenv, DB_ENV_YIELDCPU))
__os_yield(dbenv);
#endif
return (0);
err: ret = __os_get_syserr();
__db_syserr(dbenv, ret, "fcntl lock failed");
return (__db_panic(dbenv, __os_posix_err(ret)));
}
/*
* __db_fcntl_mutex_unlock --
* Release a mutex.
*
* PUBLIC: int __db_fcntl_mutex_unlock __P((DB_ENV *, db_mutex_t));
*/
int
__db_fcntl_mutex_unlock(dbenv, mutex)
DB_ENV *dbenv;
db_mutex_t mutex;
{
DB_MUTEX *mutexp;
DB_MUTEXMGR *mtxmgr;
DB_MUTEXREGION *mtxregion;
if (!MUTEX_ON(dbenv) || F_ISSET(dbenv, DB_ENV_NOLOCKING))
return (0);
mtxmgr = dbenv->mutex_handle;
mtxregion = mtxmgr->reginfo.primary;
mutexp = MUTEXP_SET(mutex);
#ifdef DIAGNOSTIC
if (!F_ISSET(mutexp, DB_MUTEX_LOCKED)) {
__db_errx(dbenv, "fcntl unlock failed: lock already unlocked");
return (__db_panic(dbenv, EACCES));
}
#endif
/*
* Release the resource. We don't have to acquire any locks because
* processes trying to acquire the lock are waiting for the flag to
* go to 0. Once that happens the waiters will serialize acquiring
* an exclusive kernel lock before locking the mutex.
*/
F_CLR(mutexp, DB_MUTEX_LOCKED);
return (0);
}
/*
* __db_fcntl_mutex_destroy --
* Destroy a mutex.
*
* PUBLIC: int __db_fcntl_mutex_destroy __P((DB_ENV *, db_mutex_t));
*/
int
__db_fcntl_mutex_destroy(dbenv, mutex)
DB_ENV *dbenv;
db_mutex_t mutex;
{
COMPQUIET(dbenv, NULL);
COMPQUIET(mutex, MUTEX_INVALID);
return (0);
}
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