mut_tas.c   [plain text]

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996-2003
 *	Sleepycat Software.  All rights reserved.
 */

#include "db_config.h"

#ifndef lint
static const char revid[] = "$Id: mut_tas.c,v 1.2 2004/03/30 01:23:45 jtownsen Exp $";
#endif /* not lint */

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

#include <stdlib.h>
#include <string.h>
#endif

/*
 * This is where we load in the actual test-and-set mutex code.
 */
#define	LOAD_ACTUAL_MUTEX_CODE
#include "db_int.h"

/*
 * __db_tas_mutex_init --
 *	Initialize a DB_MUTEX.
 *
 * PUBLIC: int __db_tas_mutex_init __P((DB_ENV *, DB_MUTEX *, u_int32_t));
 */
int
__db_tas_mutex_init(dbenv, mutexp, flags)
	DB_ENV *dbenv;
	DB_MUTEX *mutexp;
	u_int32_t flags;
{
	u_int32_t save;

	/* Check alignment. */
	DB_ASSERT(((db_alignp_t)mutexp & (MUTEX_ALIGN - 1)) == 0);

	/*
	 * The only setting/checking of the MUTEX_MPOOL flag is in the mutex
	 * mutex allocation code (__db_mutex_alloc/free).  Preserve only that
	 * flag.  This is safe because even if this flag was never explicitly
	 * set, but happened to be set in memory, it will never be checked or
	 * acted upon.
	 */
	save = F_ISSET(mutexp, MUTEX_MPOOL);
	memset(mutexp, 0, sizeof(*mutexp));
	F_SET(mutexp, save);

	/*
	 * 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);
		}
	}

	if (LF_ISSET(MUTEX_LOGICAL_LOCK))
		F_SET(mutexp, MUTEX_LOGICAL_LOCK);

	/* Initialize the lock. */
	if (MUTEX_INIT(&mutexp->tas))
		return (__os_get_errno());

#ifdef HAVE_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 *, DB_MUTEX *));
 */
int
__db_tas_mutex_lock(dbenv, mutexp)
	DB_ENV *dbenv;
	DB_MUTEX *mutexp;
{
	u_int32_t nspins;
	u_long ms, max_ms;

	if (F_ISSET(dbenv, DB_ENV_NOLOCKING) || F_ISSET(mutexp, MUTEX_IGNORE))
		return (0);

	/*
	 * Wait 1ms initially, up to 10ms for mutexes backing logical database
	 * locks, and up to 25 ms for mutual exclusion data structure mutexes.
	 * SR: #7675
	 */
	ms = 1;
	max_ms = F_ISSET(mutexp, MUTEX_LOGICAL_LOCK) ? 10 : 25;

loop:	/* Attempt to acquire the resource for N spins. */
	for (nspins = dbenv->tas_spins; nspins > 0; --nspins) {
#ifdef HAVE_MUTEX_HPPA_MSEM_INIT
relock:
#endif
#ifdef HAVE_MUTEX_S390_CC_ASSEMBLY
		tsl_t zero = 0;
#endif
		if (!MUTEX_SET(&mutexp->tas)) {
			/*
			 * Some systems (notably those with newer Intel CPUs)
			 * need a small pause here. [#6975]
			 */
#ifdef MUTEX_PAUSE
			MUTEX_PAUSE
#endif
			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) {
			__os_id(&mutexp->locked);
			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)
			__db_err(dbenv,
		"__db_tas_mutex_lock: ERROR: lock currently in use: ID: %lu",
			    (u_long)mutexp->locked);
#endif
#if defined(DIAGNOSTIC) || defined(HAVE_MUTEX_HPPA_MSEM_INIT)
		__os_id(&mutexp->locked);
#endif
		if (ms == 1)
			++mutexp->mutex_set_nowait;
		else
			++mutexp->mutex_set_wait;
		return (0);
	}

	/*
	 * Yield the processor.
	 */
	__os_yield(NULL, ms * USEC_PER_MS);
	if ((ms <<= 1) > max_ms)
		ms = max_ms;

	goto loop;
}

/*
 * __db_tas_mutex_unlock --
 *	Release a lock.
 *
 * PUBLIC: int __db_tas_mutex_unlock __P((DB_ENV *, DB_MUTEX *));
 */
int
__db_tas_mutex_unlock(dbenv, mutexp)
	DB_ENV *dbenv;
	DB_MUTEX *mutexp;
{
	if (F_ISSET(dbenv, DB_ENV_NOLOCKING) || F_ISSET(mutexp, MUTEX_IGNORE))
		return (0);

#ifdef DIAGNOSTIC
	if (!mutexp->locked)
		__db_err(dbenv,
		    "__db_tas_mutex_unlock: ERROR: lock already unlocked");
#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 DB_MUTEX.
 *
 * PUBLIC: int __db_tas_mutex_destroy __P((DB_MUTEX *));
 */
int
__db_tas_mutex_destroy(mutexp)
	DB_MUTEX *mutexp;
{
	if (F_ISSET(mutexp, MUTEX_IGNORE))
		return (0);

	MUTEX_DESTROY(&mutexp->tas);

	return (0);
}