370 lines
10 KiB
C
370 lines
10 KiB
C
/* $NetBSD: pthread_cond.c,v 1.56 2010/11/02 20:49:47 skrll Exp $ */
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/*-
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* Copyright (c) 2001, 2006, 2007, 2008 The NetBSD Foundation, Inc.
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* All rights reserved.
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*
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* This code is derived from software contributed to The NetBSD Foundation
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* by Nathan J. Williams and Andrew Doran.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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/*
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* We assume that there will be no contention on pthread_cond_t::ptc_lock
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* because functioning applications must call both the wait and wakeup
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* functions while holding the same application provided mutex. The
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* spinlock is present only to prevent libpthread causing the application
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* to crash or malfunction as a result of corrupted data structures, in
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* the event that the application is buggy.
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*
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* If there is contention on spinlock when real-time threads are in use,
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* it could cause a deadlock due to priority inversion: the thread holding
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* the spinlock may not get CPU time to make forward progress and release
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* the spinlock to a higher priority thread that is waiting for it.
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* Contention on the spinlock will only occur with buggy applications,
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* so at the time of writing it's not considered a major bug in libpthread.
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*/
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#include <sys/cdefs.h>
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__RCSID("$NetBSD: pthread_cond.c,v 1.56 2010/11/02 20:49:47 skrll Exp $");
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#include <errno.h>
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#include <sys/time.h>
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#include <sys/types.h>
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#include "pthread.h"
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#include "pthread_int.h"
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int _sys___nanosleep50(const struct timespec *, struct timespec *);
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extern int pthread__started;
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static int pthread_cond_wait_nothread(pthread_t, pthread_mutex_t *,
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const struct timespec *);
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int _pthread_cond_has_waiters_np(pthread_cond_t *);
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__weak_alias(pthread_cond_has_waiters_np,_pthread_cond_has_waiters_np)
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__strong_alias(__libc_cond_init,pthread_cond_init)
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__strong_alias(__libc_cond_signal,pthread_cond_signal)
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__strong_alias(__libc_cond_broadcast,pthread_cond_broadcast)
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__strong_alias(__libc_cond_wait,pthread_cond_wait)
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__strong_alias(__libc_cond_timedwait,pthread_cond_timedwait)
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__strong_alias(__libc_cond_destroy,pthread_cond_destroy)
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int
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pthread_cond_init(pthread_cond_t *cond, const pthread_condattr_t *attr)
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{
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pthread__error(EINVAL, "Invalid condition variable attribute",
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(attr == NULL) || (attr->ptca_magic == _PT_CONDATTR_MAGIC));
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cond->ptc_magic = _PT_COND_MAGIC;
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pthread_lockinit(&cond->ptc_lock);
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PTQ_INIT(&cond->ptc_waiters);
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cond->ptc_mutex = NULL;
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return 0;
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}
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int
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pthread_cond_destroy(pthread_cond_t *cond)
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{
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pthread__error(EINVAL, "Invalid condition variable",
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cond->ptc_magic == _PT_COND_MAGIC);
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pthread__error(EBUSY, "Destroying condition variable in use",
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cond->ptc_mutex == NULL);
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cond->ptc_magic = _PT_COND_DEAD;
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return 0;
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}
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inline int
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pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex,
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const struct timespec *abstime)
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{
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pthread_t self;
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int retval;
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pthread__error(EINVAL, "Invalid condition variable",
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cond->ptc_magic == _PT_COND_MAGIC);
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pthread__error(EINVAL, "Invalid mutex",
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mutex->ptm_magic == _PT_MUTEX_MAGIC);
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pthread__error(EPERM, "Mutex not locked in condition wait",
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mutex->ptm_owner != NULL);
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if (abstime != NULL) {
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pthread__error(EINVAL, "Invalid wait time",
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(abstime->tv_sec >= 0) &&
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(abstime->tv_nsec >= 0) &&
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(abstime->tv_nsec < 1000000000));
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}
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self = pthread__self();
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/* Just hang out for a while if threads aren't running yet. */
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if (__predict_false(pthread__started == 0)) {
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return pthread_cond_wait_nothread(self, mutex, abstime);
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}
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if (__predict_false(self->pt_cancel)) {
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pthread__cancelled();
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}
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/* Note this thread as waiting on the CV. */
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pthread__spinlock(self, &cond->ptc_lock);
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cond->ptc_mutex = mutex;
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PTQ_INSERT_HEAD(&cond->ptc_waiters, self, pt_sleep);
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self->pt_sleepobj = cond;
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pthread__spinunlock(self, &cond->ptc_lock);
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do {
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self->pt_willpark = 1;
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pthread_mutex_unlock(mutex);
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self->pt_willpark = 0;
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self->pt_blocking++;
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retval = _lwp_park(abstime, self->pt_unpark,
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__UNVOLATILE(&mutex->ptm_waiters),
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__UNVOLATILE(&mutex->ptm_waiters));
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self->pt_unpark = 0;
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self->pt_blocking--;
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membar_sync();
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pthread_mutex_lock(mutex);
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/*
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* If we have cancelled then exit. POSIX dictates that
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* the mutex must be held when we action the cancellation.
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*
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* If we absorbed a pthread_cond_signal() and cannot take
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* the wakeup, we must ensure that another thread does.
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*
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* If awoke early, we may still be on the sleep queue and
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* must remove ourself.
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*/
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if (__predict_false(retval != 0)) {
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switch (errno) {
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case EINTR:
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case EALREADY:
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retval = 0;
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break;
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default:
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retval = errno;
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break;
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}
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}
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if (__predict_false(self->pt_cancel | retval)) {
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pthread_cond_signal(cond);
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if (self->pt_cancel) {
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pthread__cancelled();
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}
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break;
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}
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} while (self->pt_sleepobj != NULL);
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return retval;
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}
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int
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pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex)
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{
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return pthread_cond_timedwait(cond, mutex, NULL);
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}
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static int __noinline
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pthread__cond_wake_one(pthread_cond_t *cond)
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{
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pthread_t self, signaled;
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pthread_mutex_t *mutex;
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lwpid_t lid;
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pthread__error(EINVAL, "Invalid condition variable",
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cond->ptc_magic == _PT_COND_MAGIC);
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/*
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* Pull the first thread off the queue. If the current thread
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* is associated with the condition variable, remove it without
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* awakening (error case in pthread_cond_timedwait()).
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*/
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self = pthread__self();
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pthread__spinlock(self, &cond->ptc_lock);
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if (self->pt_sleepobj == cond) {
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PTQ_REMOVE(&cond->ptc_waiters, self, pt_sleep);
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self->pt_sleepobj = NULL;
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}
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signaled = PTQ_FIRST(&cond->ptc_waiters);
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if (__predict_false(signaled == NULL)) {
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cond->ptc_mutex = NULL;
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pthread__spinunlock(self, &cond->ptc_lock);
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return 0;
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}
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mutex = cond->ptc_mutex;
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if (PTQ_NEXT(signaled, pt_sleep) == NULL) {
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cond->ptc_mutex = NULL;
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PTQ_INIT(&cond->ptc_waiters);
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} else {
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PTQ_REMOVE(&cond->ptc_waiters, signaled, pt_sleep);
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}
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signaled->pt_sleepobj = NULL;
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lid = signaled->pt_lid;
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pthread__spinunlock(self, &cond->ptc_lock);
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/*
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* For all valid uses of pthread_cond_signal(), the caller will
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* hold the mutex that the target is using to synchronize with.
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* To avoid the target awakening and immediately blocking on the
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* mutex, transfer the thread to be awoken to the current thread's
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* deferred wakeup list. The waiter will be set running when the
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* caller (this thread) releases the mutex.
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*/
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if (__predict_false(self->pt_nwaiters == (size_t)pthread__unpark_max)) {
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(void)_lwp_unpark_all(self->pt_waiters, self->pt_nwaiters,
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__UNVOLATILE(&mutex->ptm_waiters));
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self->pt_nwaiters = 0;
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}
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self->pt_waiters[self->pt_nwaiters++] = lid;
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pthread__mutex_deferwake(self, mutex);
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return 0;
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}
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int
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pthread_cond_signal(pthread_cond_t *cond)
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{
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if (__predict_true(PTQ_EMPTY(&cond->ptc_waiters)))
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return 0;
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return pthread__cond_wake_one(cond);
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}
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static int __noinline
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pthread__cond_wake_all(pthread_cond_t *cond)
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{
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pthread_t self, signaled;
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pthread_mutex_t *mutex;
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u_int max;
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size_t nwaiters;
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pthread__error(EINVAL, "Invalid condition variable",
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cond->ptc_magic == _PT_COND_MAGIC);
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/*
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* Try to defer waking threads (see pthread_cond_signal()).
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* Only transfer waiters for which there is no pending wakeup.
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*/
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self = pthread__self();
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pthread__spinlock(self, &cond->ptc_lock);
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max = pthread__unpark_max;
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mutex = cond->ptc_mutex;
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nwaiters = self->pt_nwaiters;
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PTQ_FOREACH(signaled, &cond->ptc_waiters, pt_sleep) {
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if (__predict_false(nwaiters == max)) {
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/* Overflow. */
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(void)_lwp_unpark_all(self->pt_waiters,
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nwaiters, __UNVOLATILE(&mutex->ptm_waiters));
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nwaiters = 0;
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}
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signaled->pt_sleepobj = NULL;
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self->pt_waiters[nwaiters++] = signaled->pt_lid;
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}
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PTQ_INIT(&cond->ptc_waiters);
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self->pt_nwaiters = nwaiters;
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cond->ptc_mutex = NULL;
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pthread__spinunlock(self, &cond->ptc_lock);
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pthread__mutex_deferwake(self, mutex);
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return 0;
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}
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int
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pthread_cond_broadcast(pthread_cond_t *cond)
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{
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if (__predict_true(PTQ_EMPTY(&cond->ptc_waiters)))
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return 0;
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return pthread__cond_wake_all(cond);
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}
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int
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_pthread_cond_has_waiters_np(pthread_cond_t *cond)
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{
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return !PTQ_EMPTY(&cond->ptc_waiters);
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}
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int
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pthread_condattr_init(pthread_condattr_t *attr)
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{
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attr->ptca_magic = _PT_CONDATTR_MAGIC;
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return 0;
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}
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int
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pthread_condattr_destroy(pthread_condattr_t *attr)
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{
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pthread__error(EINVAL, "Invalid condition variable attribute",
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attr->ptca_magic == _PT_CONDATTR_MAGIC);
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attr->ptca_magic = _PT_CONDATTR_DEAD;
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return 0;
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}
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/* Utility routine to hang out for a while if threads haven't started yet. */
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static int
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pthread_cond_wait_nothread(pthread_t self, pthread_mutex_t *mutex,
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const struct timespec *abstime)
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{
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struct timespec now, diff;
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int retval;
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if (abstime == NULL) {
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diff.tv_sec = 99999999;
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diff.tv_nsec = 0;
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} else {
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clock_gettime(CLOCK_REALTIME, &now);
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if (timespeccmp(abstime, &now, <))
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timespecclear(&diff);
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else
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timespecsub(abstime, &now, &diff);
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}
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do {
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pthread__testcancel(self);
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pthread_mutex_unlock(mutex);
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retval = _sys___nanosleep50(&diff, NULL);
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pthread_mutex_lock(mutex);
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} while (abstime == NULL && retval == 0);
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pthread__testcancel(self);
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if (retval == 0)
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return ETIMEDOUT;
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else
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/* spurious wakeup */
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return 0;
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}
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