NetBSD-5.0.2/lib/libpthread/pthread_cond.c
/* $NetBSD: pthread_cond.c,v 1.53 2008/10/25 14:14:11 yamt Exp $ */
/*-
* Copyright (c) 2001, 2006, 2007, 2008 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by Nathan J. Williams and Andrew Doran.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
/*
* We assume that there will be no contention on pthread_cond_t::ptc_lock
* because functioning applications must call both the wait and wakeup
* functions while holding the same application provided mutex. The
* spinlock is present only to prevent libpthread causing the application
* to crash or malfunction as a result of corrupted data structures, in
* the event that the application is buggy.
*
* If there is contention on spinlock when real-time threads are in use,
* it could cause a deadlock due to priority inversion: the thread holding
* the spinlock may not get CPU time to make forward progress and release
* the spinlock to a higher priority thread that is waiting for it.
* Contention on the spinlock will only occur with buggy applications,
* so at the time of writing it's not considered a major bug in libpthread.
*/
#include <sys/cdefs.h>
__RCSID("$NetBSD: pthread_cond.c,v 1.53 2008/10/25 14:14:11 yamt Exp $");
#include <errno.h>
#include <sys/time.h>
#include <sys/types.h>
#include "pthread.h"
#include "pthread_int.h"
int _sys_nanosleep(const struct timespec *, struct timespec *);
extern int pthread__started;
static int pthread_cond_wait_nothread(pthread_t, pthread_mutex_t *,
const struct timespec *);
int _pthread_cond_has_waiters_np(pthread_cond_t *);
__weak_alias(pthread_cond_has_waiters_np,_pthread_cond_has_waiters_np)
__strong_alias(__libc_cond_init,pthread_cond_init)
__strong_alias(__libc_cond_signal,pthread_cond_signal)
__strong_alias(__libc_cond_broadcast,pthread_cond_broadcast)
__strong_alias(__libc_cond_wait,pthread_cond_wait)
__strong_alias(__libc_cond_timedwait,pthread_cond_timedwait)
__strong_alias(__libc_cond_destroy,pthread_cond_destroy)
int
pthread_cond_init(pthread_cond_t *cond, const pthread_condattr_t *attr)
{
pthread__error(EINVAL, "Invalid condition variable attribute",
(attr == NULL) || (attr->ptca_magic == _PT_CONDATTR_MAGIC));
cond->ptc_magic = _PT_COND_MAGIC;
pthread_lockinit(&cond->ptc_lock);
PTQ_INIT(&cond->ptc_waiters);
cond->ptc_mutex = NULL;
return 0;
}
int
pthread_cond_destroy(pthread_cond_t *cond)
{
pthread__error(EINVAL, "Invalid condition variable",
cond->ptc_magic == _PT_COND_MAGIC);
pthread__error(EBUSY, "Destroying condition variable in use",
cond->ptc_mutex == NULL);
cond->ptc_magic = _PT_COND_DEAD;
return 0;
}
inline int
pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex,
const struct timespec *abstime)
{
pthread_t self;
int retval;
pthread__error(EINVAL, "Invalid condition variable",
cond->ptc_magic == _PT_COND_MAGIC);
pthread__error(EINVAL, "Invalid mutex",
mutex->ptm_magic == _PT_MUTEX_MAGIC);
pthread__error(EPERM, "Mutex not locked in condition wait",
mutex->ptm_owner != NULL);
if (abstime != NULL) {
pthread__error(EINVAL, "Invalid wait time",
(abstime->tv_sec >= 0) &&
(abstime->tv_nsec >= 0) &&
(abstime->tv_nsec < 1000000000));
}
self = pthread__self();
/* Just hang out for a while if threads aren't running yet. */
if (__predict_false(pthread__started == 0)) {
return pthread_cond_wait_nothread(self, mutex, abstime);
}
if (__predict_false(self->pt_cancel)) {
pthread__cancelled();
}
/* Note this thread as waiting on the CV. */
pthread__spinlock(self, &cond->ptc_lock);
cond->ptc_mutex = mutex;
PTQ_INSERT_HEAD(&cond->ptc_waiters, self, pt_sleep);
self->pt_sleepobj = cond;
pthread__spinunlock(self, &cond->ptc_lock);
do {
self->pt_willpark = 1;
pthread_mutex_unlock(mutex);
self->pt_willpark = 0;
self->pt_blocking++;
retval = _lwp_park(abstime, self->pt_unpark,
__UNVOLATILE(&mutex->ptm_waiters),
__UNVOLATILE(&mutex->ptm_waiters));
self->pt_unpark = 0;
self->pt_blocking--;
membar_sync();
pthread_mutex_lock(mutex);
/*
* If we have cancelled then exit. POSIX dictates that
* the mutex must be held when we action the cancellation.
*
* If we absorbed a pthread_cond_signal() and cannot take
* the wakeup, we must ensure that another thread does.
*
* If awoke early, we may still be on the sleep queue and
* must remove ourself.
*/
if (__predict_false(retval != 0)) {
switch (errno) {
case EINTR:
case EALREADY:
retval = 0;
break;
default:
retval = errno;
break;
}
}
if (__predict_false(self->pt_cancel | retval)) {
pthread_cond_signal(cond);
if (self->pt_cancel) {
pthread__cancelled();
}
break;
}
} while (self->pt_sleepobj != NULL);
return retval;
}
int
pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex)
{
return pthread_cond_timedwait(cond, mutex, NULL);
}
static int __noinline
pthread__cond_wake_one(pthread_cond_t *cond)
{
pthread_t self, signaled;
pthread_mutex_t *mutex;
lwpid_t lid;
pthread__error(EINVAL, "Invalid condition variable",
cond->ptc_magic == _PT_COND_MAGIC);
/*
* Pull the first thread off the queue. If the current thread
* is associated with the condition variable, remove it without
* awakening (error case in pthread_cond_timedwait()).
*/
self = pthread__self();
pthread__spinlock(self, &cond->ptc_lock);
if (self->pt_sleepobj == cond) {
PTQ_REMOVE(&cond->ptc_waiters, self, pt_sleep);
self->pt_sleepobj = NULL;
}
signaled = PTQ_FIRST(&cond->ptc_waiters);
if (__predict_false(signaled == NULL)) {
cond->ptc_mutex = NULL;
pthread__spinunlock(self, &cond->ptc_lock);
return 0;
}
mutex = cond->ptc_mutex;
if (PTQ_NEXT(signaled, pt_sleep) == NULL) {
cond->ptc_mutex = NULL;
PTQ_INIT(&cond->ptc_waiters);
} else {
PTQ_REMOVE(&cond->ptc_waiters, signaled, pt_sleep);
}
signaled->pt_sleepobj = NULL;
lid = signaled->pt_lid;
pthread__spinunlock(self, &cond->ptc_lock);
/*
* For all valid uses of pthread_cond_signal(), the caller will
* hold the mutex that the target is using to synchronize with.
* To avoid the target awakening and immediatley blocking on the
* mutex, transfer the thread to be awoken to the current thread's
* deferred wakeup list. The waiter will be set running when the
* caller (this thread) releases the mutex.
*/
if (__predict_false(self->pt_nwaiters == pthread__unpark_max)) {
(void)_lwp_unpark_all(self->pt_waiters, self->pt_nwaiters,
__UNVOLATILE(&mutex->ptm_waiters));
self->pt_nwaiters = 0;
}
self->pt_waiters[self->pt_nwaiters++] = lid;
pthread__mutex_deferwake(self, mutex);
return 0;
}
int
pthread_cond_signal(pthread_cond_t *cond)
{
if (__predict_true(PTQ_EMPTY(&cond->ptc_waiters)))
return 0;
return pthread__cond_wake_one(cond);
}
static int __noinline
pthread__cond_wake_all(pthread_cond_t *cond)
{
pthread_t self, signaled;
pthread_mutex_t *mutex;
u_int max;
size_t nwaiters;
pthread__error(EINVAL, "Invalid condition variable",
cond->ptc_magic == _PT_COND_MAGIC);
/*
* Try to defer waking threads (see pthread_cond_signal()).
* Only transfer waiters for which there is no pending wakeup.
*/
self = pthread__self();
pthread__spinlock(self, &cond->ptc_lock);
max = pthread__unpark_max;
mutex = cond->ptc_mutex;
nwaiters = self->pt_nwaiters;
PTQ_FOREACH(signaled, &cond->ptc_waiters, pt_sleep) {
if (__predict_false(nwaiters == max)) {
/* Overflow. */
(void)_lwp_unpark_all(self->pt_waiters,
nwaiters, __UNVOLATILE(&mutex->ptm_waiters));
nwaiters = 0;
}
signaled->pt_sleepobj = NULL;
self->pt_waiters[nwaiters++] = signaled->pt_lid;
}
PTQ_INIT(&cond->ptc_waiters);
self->pt_nwaiters = nwaiters;
cond->ptc_mutex = NULL;
pthread__spinunlock(self, &cond->ptc_lock);
pthread__mutex_deferwake(self, mutex);
return 0;
}
int
pthread_cond_broadcast(pthread_cond_t *cond)
{
if (__predict_true(PTQ_EMPTY(&cond->ptc_waiters)))
return 0;
return pthread__cond_wake_all(cond);
}
int
_pthread_cond_has_waiters_np(pthread_cond_t *cond)
{
return !PTQ_EMPTY(&cond->ptc_waiters);
}
int
pthread_condattr_init(pthread_condattr_t *attr)
{
attr->ptca_magic = _PT_CONDATTR_MAGIC;
return 0;
}
int
pthread_condattr_destroy(pthread_condattr_t *attr)
{
pthread__error(EINVAL, "Invalid condition variable attribute",
attr->ptca_magic == _PT_CONDATTR_MAGIC);
attr->ptca_magic = _PT_CONDATTR_DEAD;
return 0;
}
/* Utility routine to hang out for a while if threads haven't started yet. */
static int
pthread_cond_wait_nothread(pthread_t self, pthread_mutex_t *mutex,
const struct timespec *abstime)
{
struct timespec now, diff;
int retval;
if (abstime == NULL) {
diff.tv_sec = 99999999;
diff.tv_nsec = 0;
} else {
clock_gettime(CLOCK_REALTIME, &now);
if (timespeccmp(abstime, &now, <))
timespecclear(&diff);
else
timespecsub(abstime, &now, &diff);
}
do {
pthread__testcancel(self);
pthread_mutex_unlock(mutex);
retval = _sys_nanosleep(&diff, NULL);
pthread_mutex_lock(mutex);
} while (abstime == NULL && retval == 0);
pthread__testcancel(self);
if (retval == 0)
return ETIMEDOUT;
else
/* spurious wakeup */
return 0;
}