freebsd-dev/lib/libthr/thread/thr_cond.c

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/*
* Copyright (c) 2005 David Xu <davidxu@freebsd.org>
* All rights reserved.
*
* 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 unmodified, 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 AUTHOR ``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 AUTHOR 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.
*
* $FreeBSD$
*/
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#include "namespace.h"
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <pthread.h>
#include <limits.h>
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#include "un-namespace.h"
#include "thr_private.h"
/*
* Prototypes
*/
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int __pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex);
int __pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex,
const struct timespec * abstime);
static int cond_init(pthread_cond_t *cond, const pthread_condattr_t *attr);
static int cond_wait_common(pthread_cond_t *cond, pthread_mutex_t *mutex,
const struct timespec *abstime, int cancel);
static int cond_signal_common(pthread_cond_t *cond, int broadcast);
/*
* Double underscore versions are cancellation points. Single underscore
* versions are not and are provided for libc internal usage (which
* shouldn't introduce cancellation points).
*/
__weak_reference(__pthread_cond_wait, pthread_cond_wait);
__weak_reference(__pthread_cond_timedwait, pthread_cond_timedwait);
__weak_reference(_pthread_cond_init, pthread_cond_init);
__weak_reference(_pthread_cond_destroy, pthread_cond_destroy);
__weak_reference(_pthread_cond_signal, pthread_cond_signal);
__weak_reference(_pthread_cond_broadcast, pthread_cond_broadcast);
static int
cond_init(pthread_cond_t *cond, const pthread_condattr_t *cond_attr)
{
pthread_cond_t pcond;
int rval = 0;
if ((pcond = (pthread_cond_t)
calloc(1, sizeof(struct pthread_cond))) == NULL) {
rval = ENOMEM;
} else {
/*
* Initialise the condition variable structure:
*/
if (cond_attr == NULL || *cond_attr == NULL) {
pcond->c_pshared = 0;
pcond->c_clockid = CLOCK_REALTIME;
} else {
pcond->c_pshared = (*cond_attr)->c_pshared;
pcond->c_clockid = (*cond_attr)->c_clockid;
}
_thr_umutex_init(&pcond->c_lock);
*cond = pcond;
}
/* Return the completion status: */
return (rval);
}
static int
init_static(struct pthread *thread, pthread_cond_t *cond)
{
int ret;
THR_LOCK_ACQUIRE(thread, &_cond_static_lock);
if (*cond == NULL)
ret = cond_init(cond, NULL);
else
ret = 0;
THR_LOCK_RELEASE(thread, &_cond_static_lock);
return (ret);
}
int
_pthread_cond_init(pthread_cond_t *cond, const pthread_condattr_t *cond_attr)
{
*cond = NULL;
return (cond_init(cond, cond_attr));
}
int
_pthread_cond_destroy(pthread_cond_t *cond)
{
struct pthread *curthread = _get_curthread();
struct pthread_cond *cv;
int rval = 0;
if (*cond == NULL)
rval = EINVAL;
else {
cv = *cond;
THR_UMUTEX_LOCK(curthread, &cv->c_lock);
/*
* NULL the caller's pointer now that the condition
* variable has been destroyed:
*/
*cond = NULL;
THR_UMUTEX_UNLOCK(curthread, &cv->c_lock);
/*
* Free the memory allocated for the condition
* variable structure:
*/
free(cv);
}
/* Return the completion status: */
return (rval);
}
struct cond_cancel_info
{
pthread_mutex_t *mutex;
pthread_cond_t *cond;
int count;
};
static void
cond_cancel_handler(void *arg)
{
struct pthread *curthread = _get_curthread();
struct cond_cancel_info *info = (struct cond_cancel_info *)arg;
pthread_cond_t cv;
if (info->cond != NULL) {
cv = *(info->cond);
THR_UMUTEX_UNLOCK(curthread, &cv->c_lock);
}
_mutex_cv_lock(info->mutex, info->count);
}
static int
cond_wait_common(pthread_cond_t *cond, pthread_mutex_t *mutex,
const struct timespec *abstime, int cancel)
{
struct pthread *curthread = _get_curthread();
struct timespec ts, ts2, *tsp;
struct cond_cancel_info info;
pthread_cond_t cv;
int ret = 0;
/*
* If the condition variable is statically initialized,
* perform the dynamic initialization:
*/
if (__predict_false(*cond == NULL &&
(ret = init_static(curthread, cond)) != 0))
return (ret);
cv = *cond;
THR_UMUTEX_LOCK(curthread, &cv->c_lock);
ret = _mutex_cv_unlock(mutex, &info.count);
if (ret) {
THR_UMUTEX_UNLOCK(curthread, &cv->c_lock);
return (ret);
Make libthr async-signal-safe without costly signal masking. The guidlines I followed are: Only 3 functions (pthread_cancel, pthread_setcancelstate, pthread_setcanceltype) are required to be async-signal-safe by POSIX. None of the rest of the pthread api is required to be async-signal-safe. This means that only the three mentioned functions are safe to use from inside signal handlers. However, there are certain system/libc calls that are cancellation points that a caller may call from within a signal handler, and since they are cancellation points calls have to be made into libthr to test for cancellation and exit the thread if necessary. So, the cancellation test and thread exit code paths must be async-signal-safe as well. A summary of the changes follows: o Almost all of the code paths that masked signals, as well as locking the pthread structure now lock only the pthread structure. o Signals are masked (and left that way) as soon as a thread enters pthread_exit(). o The active and dead threads locks now explicitly require that signals are masked. o Access to the isdead field of the pthread structure is protected by both the active and dead list locks for writing. Either one is sufficient for reading. o The thread state and type fields have been combined into one three-state switch to make it easier to read without requiring a lock. It doesn't need a lock for writing (and therefore for reading either) because only the current thread can write to it and it is an integer value. o The thread state field of the pthread structure has been eliminated. It was an unnecessary field that mostly duplicated the flags field, but required additional locking that would make a lot more code paths require signal masking. Any truly unique values (such as PS_DEAD) have been reborn as separate members of the pthread structure. o Since the mutex and condvar pthread functions are not async-signal-safe there is no need to muck about with the wait queues when handling a signal ... o ... which also removes the need for wrapping signal handlers and sigaction(2). o The condvar and mutex async-cancellation code had to be revised as a result of some of these changes, which resulted in semi-unrelated changes which would have been difficult to work on as a separate commit, so they are included as well. The only part of the changes I am worried about is related to locking for the pthread joining fields. But, I will take a closer look at them once this mega-patch is committed.
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}
info.mutex = mutex;
info.cond = cond;
if (abstime != NULL) {
clock_gettime(cv->c_clockid, &ts);
TIMESPEC_SUB(&ts2, abstime, &ts);
tsp = &ts2;
} else
tsp = NULL;
if (cancel) {
THR_CLEANUP_PUSH(curthread, cond_cancel_handler, &info);
_thr_cancel_enter_defer(curthread);
ret = _thr_ucond_wait(&cv->c_kerncv, &cv->c_lock, tsp, 1);
info.cond = NULL;
_thr_cancel_leave_defer(curthread, ret);
THR_CLEANUP_POP(curthread, 0);
} else {
ret = _thr_ucond_wait(&cv->c_kerncv, &cv->c_lock, tsp, 0);
}
if (ret == EINTR)
ret = 0;
_mutex_cv_lock(mutex, info.count);
return (ret);
}
int
_pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex)
{
return (cond_wait_common(cond, mutex, NULL, 0));
}
int
__pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex)
{
return (cond_wait_common(cond, mutex, NULL, 1));
}
int
_pthread_cond_timedwait(pthread_cond_t * cond, pthread_mutex_t * mutex,
const struct timespec * abstime)
{
if (abstime == NULL || abstime->tv_sec < 0 || abstime->tv_nsec < 0 ||
abstime->tv_nsec >= 1000000000)
Make libthr async-signal-safe without costly signal masking. The guidlines I followed are: Only 3 functions (pthread_cancel, pthread_setcancelstate, pthread_setcanceltype) are required to be async-signal-safe by POSIX. None of the rest of the pthread api is required to be async-signal-safe. This means that only the three mentioned functions are safe to use from inside signal handlers. However, there are certain system/libc calls that are cancellation points that a caller may call from within a signal handler, and since they are cancellation points calls have to be made into libthr to test for cancellation and exit the thread if necessary. So, the cancellation test and thread exit code paths must be async-signal-safe as well. A summary of the changes follows: o Almost all of the code paths that masked signals, as well as locking the pthread structure now lock only the pthread structure. o Signals are masked (and left that way) as soon as a thread enters pthread_exit(). o The active and dead threads locks now explicitly require that signals are masked. o Access to the isdead field of the pthread structure is protected by both the active and dead list locks for writing. Either one is sufficient for reading. o The thread state and type fields have been combined into one three-state switch to make it easier to read without requiring a lock. It doesn't need a lock for writing (and therefore for reading either) because only the current thread can write to it and it is an integer value. o The thread state field of the pthread structure has been eliminated. It was an unnecessary field that mostly duplicated the flags field, but required additional locking that would make a lot more code paths require signal masking. Any truly unique values (such as PS_DEAD) have been reborn as separate members of the pthread structure. o Since the mutex and condvar pthread functions are not async-signal-safe there is no need to muck about with the wait queues when handling a signal ... o ... which also removes the need for wrapping signal handlers and sigaction(2). o The condvar and mutex async-cancellation code had to be revised as a result of some of these changes, which resulted in semi-unrelated changes which would have been difficult to work on as a separate commit, so they are included as well. The only part of the changes I am worried about is related to locking for the pthread joining fields. But, I will take a closer look at them once this mega-patch is committed.
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return (EINVAL);
return (cond_wait_common(cond, mutex, abstime, 0));
}
int
__pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex,
const struct timespec *abstime)
{
if (abstime == NULL || abstime->tv_sec < 0 || abstime->tv_nsec < 0 ||
abstime->tv_nsec >= 1000000000)
return (EINVAL);
return (cond_wait_common(cond, mutex, abstime, 1));
}
static int
cond_signal_common(pthread_cond_t *cond, int broadcast)
{
struct pthread *curthread = _get_curthread();
pthread_cond_t cv;
int ret = 0;
/*
* If the condition variable is statically initialized, perform dynamic
* initialization.
*/
if (__predict_false(*cond == NULL &&
(ret = init_static(curthread, cond)) != 0))
return (ret);
cv = *cond;
THR_UMUTEX_LOCK(curthread, &cv->c_lock);
if (!broadcast)
ret = _thr_ucond_signal(&cv->c_kerncv);
else
ret = _thr_ucond_broadcast(&cv->c_kerncv);
THR_UMUTEX_UNLOCK(curthread, &cv->c_lock);
return (ret);
}
int
_pthread_cond_signal(pthread_cond_t * cond)
{
return (cond_signal_common(cond, 0));
}
int
_pthread_cond_broadcast(pthread_cond_t * cond)
{
return (cond_signal_common(cond, 1));
}