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/*-
* See the file LICENSE for redistribution information.
*
* Copyright (c) 1996, 1997, 1998, 1999, 2000
* Sleepycat Software. All rights reserved.
*/
#include "db_config.h"
#ifndef lint
static const char revid[] = "$Id: mut_tas.c,v 11.18 2000/11/30 00:58:41 ubell Exp $";
#endif /* not lint */
#ifndef NO_SYSTEM_INCLUDES
#include <sys/types.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#endif
/*
* This is where we load in the actual test-and-set mutex code.
*/
#define LOAD_ACTUAL_MUTEX_CODE
#include "db_int.h"
#ifdef DIAGNOSTIC
#undef MSG1
#define MSG1 "mutex_lock: ERROR: lock currently in use: pid: %lu.\n"
#undef MSG2
#define MSG2 "mutex_unlock: ERROR: lock already unlocked\n"
#ifndef STDERR_FILENO
#define STDERR_FILENO 2
#endif
#endif
/*
* __db_tas_mutex_init --
* Initialize a MUTEX.
*
* PUBLIC: int __db_tas_mutex_init __P((DB_ENV *, MUTEX *, u_int32_t));
*/
int
__db_tas_mutex_init(dbenv, mutexp, flags)
DB_ENV *dbenv;
MUTEX *mutexp;
u_int32_t flags;
{
/* Check alignment. */
DB_ASSERT(((db_alignp_t)mutexp & (MUTEX_ALIGN - 1)) == 0);
memset(mutexp, 0, sizeof(*mutexp));
/*
* If this is a thread lock or the process has told us that there are
* no other processes in the environment, use thread-only locks, they
* are faster in some cases.
*
* This is where we decide to ignore locks we don't need to set -- if
* the application isn't threaded, there aren't any threads to block.
*/
if (LF_ISSET(MUTEX_THREAD) || F_ISSET(dbenv, DB_ENV_PRIVATE)) {
if (!F_ISSET(dbenv, DB_ENV_THREAD)) {
F_SET(mutexp, MUTEX_IGNORE);
return (0);
}
F_SET(mutexp, MUTEX_THREAD);
}
/* Initialize the lock. */
if (MUTEX_INIT(&mutexp->tas))
return (__os_get_errno());
mutexp->spins = __os_spin();
#ifdef MUTEX_SYSTEM_RESOURCES
mutexp->reg_off = INVALID_ROFF;
#endif
F_SET(mutexp, MUTEX_INITED);
return (0);
}
/*
* __db_tas_mutex_lock
* Lock on a mutex, logically blocking if necessary.
*
* PUBLIC: int __db_tas_mutex_lock __P((DB_ENV *, MUTEX *));
*/
int
__db_tas_mutex_lock(dbenv, mutexp)
DB_ENV *dbenv;
MUTEX *mutexp;
{
u_long ms;
int nspins;
if (!dbenv->db_mutexlocks || F_ISSET(mutexp, MUTEX_IGNORE))
return (0);
ms = 1;
loop: /* Attempt to acquire the resource for N spins. */
for (nspins = mutexp->spins; nspins > 0; --nspins) {
#ifdef HAVE_MUTEX_HPPA_MSEM_INIT
relock:
#endif
if (!MUTEX_SET(&mutexp->tas))
continue;
#ifdef HAVE_MUTEX_HPPA_MSEM_INIT
/*
* HP semaphores are unlocked automatically when a holding
* process exits. If the mutex appears to be locked
* (mutexp->locked != 0) but we got here, assume this has
* happened. Stick our own pid into mutexp->locked and
* lock again. (The default state of the mutexes used to
* block in __lock_get_internal is locked, so exiting with
* a locked mutex is reasonable behavior for a process that
* happened to initialize or use one of them.)
*/
if (mutexp->locked != 0) {
mutexp->locked = (u_int32_t)getpid();
goto relock;
}
/*
* If we make it here, locked == 0, the diagnostic won't fire,
* and we were really unlocked by someone calling the
* DB mutex unlock function.
*/
#endif
#ifdef DIAGNOSTIC
if (mutexp->locked != 0) {
char msgbuf[128];
(void)snprintf(msgbuf,
sizeof(msgbuf), MSG1, (u_long)mutexp->locked);
(void)write(STDERR_FILENO, msgbuf, strlen(msgbuf));
}
#endif
#if defined(DIAGNOSTIC) || defined(HAVE_MUTEX_HPPA_MSEM_INIT)
mutexp->locked = (u_int32_t)getpid();
#endif
if (ms == 1)
++mutexp->mutex_set_nowait;
else
++mutexp->mutex_set_wait;
return (0);
}
/* Yield the processor; wait 1ms initially, up to 1 second. */
__os_yield(NULL, ms * USEC_PER_MS);
if ((ms <<= 1) > MS_PER_SEC)
ms = MS_PER_SEC;
goto loop;
}
/*
* __db_tas_mutex_unlock --
* Release a lock.
*
* PUBLIC: int __db_tas_mutex_unlock __P((DB_ENV *, MUTEX *));
*/
int
__db_tas_mutex_unlock(dbenv, mutexp)
DB_ENV *dbenv;
MUTEX *mutexp;
{
if (!dbenv->db_mutexlocks || F_ISSET(mutexp, MUTEX_IGNORE))
return (0);
#ifdef DIAGNOSTIC
if (!mutexp->locked)
(void)write(STDERR_FILENO, MSG2, sizeof(MSG2) - 1);
#endif
#if defined(DIAGNOSTIC) || defined(HAVE_MUTEX_HPPA_MSEM_INIT)
mutexp->locked = 0;
#endif
MUTEX_UNSET(&mutexp->tas);
return (0);
}
/*
* __db_tas_mutex_destroy --
* Destroy a MUTEX.
*
* PUBLIC: int __db_tas_mutex_destroy __P((MUTEX *));
*/
int
__db_tas_mutex_destroy(mutexp)
MUTEX *mutexp;
{
if (F_ISSET(mutexp, MUTEX_IGNORE))
return (0);
MUTEX_DESTROY(&mutexp->tas);
return (0);
}
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