mirror of
https://git.FreeBSD.org/src.git
synced 2024-12-09 09:40:42 +00:00
Rewrite rwlock to user atomic operations to change rwlock state, this
eliminates internal mutex lock contention when most rwlock operations are read. Orignal patch provided by: jeff
This commit is contained in:
parent
b81b7f0a7d
commit
5ab512bb8e
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=177770
@ -290,3 +290,56 @@ _pthread_cond_broadcast(pthread_cond_t * cond)
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return (cond_signal_common(cond, 1));
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}
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int
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_pthread_cond_wait_unlocked(pthread_cond_t *cond, pthread_mutex_t *mutex,
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const struct timespec *abstime)
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{
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struct pthread *curthread = _get_curthread();
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struct timespec ts, ts2, *tsp;
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pthread_cond_t cv;
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int ret;
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cv = *cond;
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THR_UMUTEX_LOCK(curthread, &cv->c_lock);
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_pthread_mutex_unlock(mutex);
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if (abstime != NULL) {
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clock_gettime(cv->c_clockid, &ts);
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TIMESPEC_SUB(&ts2, abstime, &ts);
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tsp = &ts2;
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} else
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tsp = NULL;
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ret = _thr_ucond_wait(&cv->c_kerncv, &cv->c_lock, tsp, 0);
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if (ret == EINTR)
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ret = 0;
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return (ret);
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}
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int
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_pthread_cond_broadcast_unlock(pthread_cond_t *cond, pthread_mutex_t *mutex, int broadcast)
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{
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struct pthread *curthread = _get_curthread();
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pthread_cond_t cv;
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int ret = 0;
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/*
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* If the condition variable is statically initialized, perform dynamic
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* initialization.
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*/
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if (__predict_false(*cond == NULL &&
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(ret = init_static(curthread, cond)) != 0))
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return (ret);
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cv = *cond;
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THR_UMUTEX_LOCK(curthread, &cv->c_lock);
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_pthread_mutex_unlock(mutex);
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if (!broadcast)
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ret = _thr_ucond_signal(&cv->c_kerncv);
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else
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ret = _thr_ucond_broadcast(&cv->c_kerncv);
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THR_UMUTEX_UNLOCK(curthread, &cv->c_lock);
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return (ret);
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}
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@ -275,8 +275,10 @@ struct pthread_rwlock {
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pthread_mutex_t lock; /* monitor lock */
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pthread_cond_t read_signal;
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pthread_cond_t write_signal;
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int state; /* 0 = idle >0 = # of readers -1 = writer */
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volatile int32_t state;
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int blocked_writers;
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int blocked_readers;
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struct pthread *owner;
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};
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/*
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@ -673,6 +675,8 @@ void _thread_bp_death(void);
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int _sched_yield(void);
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int _pthread_getaffinity_np(pthread_t, size_t, cpuset_t *);
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int _pthread_setaffinity_np(pthread_t, size_t, const cpuset_t *);
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int _pthread_cond_wait_unlocked(pthread_cond_t *, pthread_mutex_t *, const struct timespec *) __hidden;
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int _pthread_cond_broadcast_unlock(pthread_cond_t *, pthread_mutex_t *, int broadcast);
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/* #include <fcntl.h> */
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#ifdef _SYS_FCNTL_H_
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@ -35,8 +35,11 @@
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#include "un-namespace.h"
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#include "thr_private.h"
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/* maximum number of times a read lock may be obtained */
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#define MAX_READ_LOCKS (INT_MAX - 1)
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#define RWLOCK_WRITE_OWNER 0x80000000U
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#define RWLOCK_WRITE_WAITERS 0x40000000U
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#define RWLOCK_READ_WAITERS 0x20000000U
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#define RWLOCK_MAX_READERS 0x1fffffffU
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#define RWLOCK_READER_COUNT(c) ((c) & RWLOCK_MAX_READERS)
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__weak_reference(_pthread_rwlock_destroy, pthread_rwlock_destroy);
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__weak_reference(_pthread_rwlock_init, pthread_rwlock_init);
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@ -85,7 +88,9 @@ rwlock_init(pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr __unused)
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} else {
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/* success */
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prwlock->state = 0;
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prwlock->blocked_readers = 0;
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prwlock->blocked_writers = 0;
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prwlock->owner = NULL;
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*rwlock = prwlock;
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}
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}
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@ -105,14 +110,13 @@ _pthread_rwlock_destroy (pthread_rwlock_t *rwlock)
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pthread_rwlock_t prwlock;
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prwlock = *rwlock;
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*rwlock = NULL;
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_pthread_mutex_destroy(&prwlock->lock);
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_pthread_cond_destroy(&prwlock->read_signal);
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_pthread_cond_destroy(&prwlock->write_signal);
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free(prwlock);
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*rwlock = NULL;
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ret = 0;
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}
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return (ret);
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@ -142,37 +146,66 @@ _pthread_rwlock_init (pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr
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return (rwlock_init(rwlock, attr));
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}
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static inline int
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rwlock_tryrdlock(struct pthread_rwlock *prwlock, int prefer_reader)
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{
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int32_t state;
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int32_t wrflags;
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if (prefer_reader)
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wrflags = RWLOCK_WRITE_OWNER;
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else
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wrflags = RWLOCK_WRITE_OWNER | RWLOCK_WRITE_WAITERS;
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state = prwlock->state;
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while (!(state & wrflags)) {
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if (RWLOCK_READER_COUNT(state) == RWLOCK_MAX_READERS)
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return (EAGAIN);
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if (atomic_cmpset_acq_32(&prwlock->state, state, state + 1))
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return (0);
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CPU_SPINWAIT;
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state = prwlock->state;
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}
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return (EBUSY);
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}
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static int
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rwlock_rdlock_common (pthread_rwlock_t *rwlock, const struct timespec *abstime)
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rwlock_rdlock_common(pthread_rwlock_t *rwlock, const struct timespec *abstime)
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{
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struct pthread *curthread = _get_curthread();
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const int prefer_read = curthread->rdlock_count > 0;
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pthread_rwlock_t prwlock;
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int ret;
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int ret, wrflags, old;
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int32_t state;
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if (rwlock == NULL)
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if (__predict_false(rwlock == NULL))
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return (EINVAL);
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prwlock = *rwlock;
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/* check for static initialization */
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if (prwlock == NULL) {
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if (__predict_false(prwlock == NULL)) {
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if ((ret = init_static(curthread, rwlock)) != 0)
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return (ret);
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prwlock = *rwlock;
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}
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/* grab the monitor lock */
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if ((ret = _pthread_mutex_lock(&prwlock->lock)) != 0)
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/*
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* POSIX said the validity of the abstimeout parameter need
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* not be checked if the lock can be immediately acquired.
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*/
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ret = rwlock_tryrdlock(prwlock, prefer_read);
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if (ret == 0) {
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curthread->rdlock_count++;
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return (ret);
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/* check lock count */
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if (prwlock->state == MAX_READ_LOCKS) {
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_pthread_mutex_unlock(&prwlock->lock);
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return (EAGAIN);
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}
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if ((curthread->rdlock_count > 0) && (prwlock->state > 0)) {
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if (__predict_false(abstime &&
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(abstime->tv_nsec >= 1000000000 || abstime->tv_nsec < 0)))
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return (EINVAL);
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if (prefer_read) {
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/*
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* To avoid having to track all the rdlocks held by
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* a thread or all of the threads that hold a rdlock,
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@ -185,36 +218,51 @@ rwlock_rdlock_common (pthread_rwlock_t *rwlock, const struct timespec *abstime)
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* when it already has one or more rdlocks avoids the
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* deadlock. I hope the reader can follow that logic ;-)
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*/
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; /* nothing needed */
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} else {
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/* give writers priority over readers */
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while (prwlock->blocked_writers || prwlock->state < 0) {
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if (abstime)
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ret = _pthread_cond_timedwait
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(&prwlock->read_signal,
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&prwlock->lock, abstime);
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else
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ret = _pthread_cond_wait(&prwlock->read_signal,
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&prwlock->lock);
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if (ret != 0) {
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/* can't do a whole lot if this fails */
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_pthread_mutex_unlock(&prwlock->lock);
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return (ret);
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}
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wrflags = RWLOCK_WRITE_OWNER;
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} else
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wrflags = RWLOCK_WRITE_OWNER | RWLOCK_WRITE_WAITERS;
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/* reset to zero */
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ret = 0;
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for (;;) {
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_pthread_mutex_lock(&prwlock->lock);
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state = prwlock->state;
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/* set read contention bit */
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while ((state & wrflags) && !(state & RWLOCK_READ_WAITERS)) {
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if (atomic_cmpset_acq_32(&prwlock->state, state, state | RWLOCK_READ_WAITERS))
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break;
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CPU_SPINWAIT;
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state = prwlock->state;
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}
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atomic_add_32(&prwlock->blocked_readers, 1);
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if (state & wrflags) {
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ret = _pthread_cond_wait_unlocked(&prwlock->read_signal, &prwlock->lock, abstime);
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old = atomic_fetchadd_32(&prwlock->blocked_readers, -1);
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if (old == 1)
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_pthread_mutex_lock(&prwlock->lock);
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else
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goto try_it;
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} else {
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atomic_subtract_32(&prwlock->blocked_readers, 1);
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}
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if (prwlock->blocked_readers == 0)
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atomic_clear_32(&prwlock->state, RWLOCK_READ_WAITERS);
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_pthread_mutex_unlock(&prwlock->lock);
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try_it:
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/* try to lock it again. */
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if (rwlock_tryrdlock(prwlock, prefer_read) == 0) {
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curthread->rdlock_count++;
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ret = 0;
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break;
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}
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if (ret)
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break;
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}
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curthread->rdlock_count++;
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prwlock->state++; /* indicate we are locked for reading */
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/*
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* Something is really wrong if this call fails. Returning
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* error won't do because we've already obtained the read
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* lock. Decrementing 'state' is no good because we probably
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* don't have the monitor lock.
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*/
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_pthread_mutex_unlock(&prwlock->lock);
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return (ret);
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}
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@ -238,44 +286,40 @@ _pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock)
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pthread_rwlock_t prwlock;
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int ret;
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if (rwlock == NULL)
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if (__predict_false(rwlock == NULL))
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return (EINVAL);
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prwlock = *rwlock;
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/* check for static initialization */
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if (prwlock == NULL) {
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if (__predict_false(prwlock == NULL)) {
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if ((ret = init_static(curthread, rwlock)) != 0)
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return (ret);
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prwlock = *rwlock;
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}
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/* grab the monitor lock */
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if ((ret = _pthread_mutex_lock(&prwlock->lock)) != 0)
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return (ret);
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if (prwlock->state == MAX_READ_LOCKS)
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ret = EAGAIN;
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else if ((curthread->rdlock_count > 0) && (prwlock->state > 0)) {
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/* see comment for pthread_rwlock_rdlock() */
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ret = rwlock_tryrdlock(prwlock, curthread->rdlock_count > 0);
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if (ret == 0)
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curthread->rdlock_count++;
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prwlock->state++;
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}
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/* give writers priority over readers */
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else if (prwlock->blocked_writers || prwlock->state < 0)
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ret = EBUSY;
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else {
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curthread->rdlock_count++;
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prwlock->state++; /* indicate we are locked for reading */
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}
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/* see the comment on this in pthread_rwlock_rdlock */
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_pthread_mutex_unlock(&prwlock->lock);
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return (ret);
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}
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static inline int
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rwlock_trywrlock(struct pthread_rwlock *prwlock)
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{
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int32_t state;
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state = prwlock->state;
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while (!(state & RWLOCK_WRITE_OWNER) && RWLOCK_READER_COUNT(state) == 0) {
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if (atomic_cmpset_acq_32(&prwlock->state, state, state | RWLOCK_WRITE_OWNER))
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return (0);
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CPU_SPINWAIT;
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state = prwlock->state;
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}
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return (EBUSY);
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}
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int
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_pthread_rwlock_trywrlock (pthread_rwlock_t *rwlock)
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{
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@ -283,72 +327,22 @@ _pthread_rwlock_trywrlock (pthread_rwlock_t *rwlock)
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pthread_rwlock_t prwlock;
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int ret;
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if (rwlock == NULL)
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if (__predict_false(rwlock == NULL))
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return (EINVAL);
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prwlock = *rwlock;
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/* check for static initialization */
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if (prwlock == NULL) {
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if (__predict_false(prwlock == NULL)) {
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if ((ret = init_static(curthread, rwlock)) != 0)
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return (ret);
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prwlock = *rwlock;
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}
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/* grab the monitor lock */
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if ((ret = _pthread_mutex_lock(&prwlock->lock)) != 0)
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return (ret);
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if (prwlock->state != 0)
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ret = EBUSY;
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else
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/* indicate we are locked for writing */
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prwlock->state = -1;
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/* see the comment on this in pthread_rwlock_rdlock */
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_pthread_mutex_unlock(&prwlock->lock);
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return (ret);
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}
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int
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_pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
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{
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struct pthread *curthread = _get_curthread();
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pthread_rwlock_t prwlock;
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int ret;
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if (rwlock == NULL)
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return (EINVAL);
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prwlock = *rwlock;
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if (prwlock == NULL)
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return (EINVAL);
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/* grab the monitor lock */
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if ((ret = _pthread_mutex_lock(&prwlock->lock)) != 0)
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return (ret);
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if (prwlock->state > 0) {
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curthread->rdlock_count--;
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prwlock->state--;
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if (prwlock->state == 0 && prwlock->blocked_writers)
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ret = _pthread_cond_signal(&prwlock->write_signal);
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} else if (prwlock->state < 0) {
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prwlock->state = 0;
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if (prwlock->blocked_writers)
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ret = _pthread_cond_signal(&prwlock->write_signal);
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else
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ret = _pthread_cond_broadcast(&prwlock->read_signal);
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} else
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ret = EINVAL;
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/* see the comment on this in pthread_rwlock_rdlock */
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_pthread_mutex_unlock(&prwlock->lock);
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ret = rwlock_trywrlock(prwlock);
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if (ret == 0)
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prwlock->owner = curthread;
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return (ret);
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}
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@ -358,48 +352,78 @@ rwlock_wrlock_common (pthread_rwlock_t *rwlock, const struct timespec *abstime)
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struct pthread *curthread = _get_curthread();
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pthread_rwlock_t prwlock;
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int ret;
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int32_t state;
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if (rwlock == NULL)
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if (__predict_false(rwlock == NULL))
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return (EINVAL);
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prwlock = *rwlock;
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/* check for static initialization */
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if (prwlock == NULL) {
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if (__predict_false(prwlock == NULL)) {
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if ((ret = init_static(curthread, rwlock)) != 0)
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return (ret);
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prwlock = *rwlock;
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}
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/* grab the monitor lock */
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if ((ret = _pthread_mutex_lock(&prwlock->lock)) != 0)
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return (ret);
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/*
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* POSIX said the validity of the abstimeout parameter need
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* not be checked if the lock can be immediately acquired.
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*/
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/* try to lock it in userland */
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ret = rwlock_trywrlock(prwlock);
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if (ret == 0) {
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prwlock->owner = curthread;
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return (ret);
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}
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if (__predict_false(abstime &&
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(abstime->tv_nsec >= 1000000000 || abstime->tv_nsec < 0)))
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return (EINVAL);
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/* reset to zero */
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ret = 0;
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for (;;) {
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_pthread_mutex_lock(&prwlock->lock);
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state = prwlock->state;
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while (((state & RWLOCK_WRITE_OWNER) || RWLOCK_READER_COUNT(state) != 0) &&
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(state & RWLOCK_WRITE_WAITERS) == 0) {
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if (atomic_cmpset_acq_32(&prwlock->state, state, state | RWLOCK_WRITE_WAITERS))
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break;
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CPU_SPINWAIT;
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state = prwlock->state;
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||||
}
|
||||
|
||||
while (prwlock->state != 0) {
|
||||
prwlock->blocked_writers++;
|
||||
|
||||
if (abstime != NULL)
|
||||
ret = _pthread_cond_timedwait(&prwlock->write_signal,
|
||||
&prwlock->lock, abstime);
|
||||
else
|
||||
ret = _pthread_cond_wait(&prwlock->write_signal,
|
||||
&prwlock->lock);
|
||||
if (ret != 0) {
|
||||
prwlock->blocked_writers--;
|
||||
_pthread_mutex_unlock(&prwlock->lock);
|
||||
return (ret);
|
||||
while ((state & RWLOCK_WRITE_OWNER) || RWLOCK_READER_COUNT(state) != 0) {
|
||||
if (abstime == NULL)
|
||||
ret = _pthread_cond_wait(&prwlock->write_signal, &prwlock->lock);
|
||||
else
|
||||
ret = _pthread_cond_timedwait(&prwlock->write_signal, &prwlock->lock, abstime);
|
||||
|
||||
if (ret)
|
||||
break;
|
||||
state = prwlock->state;
|
||||
}
|
||||
|
||||
prwlock->blocked_writers--;
|
||||
if (prwlock->blocked_writers == 0)
|
||||
atomic_clear_32(&prwlock->state, RWLOCK_WRITE_WAITERS);
|
||||
_pthread_mutex_unlock(&prwlock->lock);
|
||||
|
||||
if (rwlock_trywrlock(prwlock) == 0) {
|
||||
prwlock->owner = curthread;
|
||||
ret = 0;
|
||||
break;
|
||||
}
|
||||
|
||||
if (ret)
|
||||
break;
|
||||
}
|
||||
|
||||
/* indicate we are locked for writing */
|
||||
prwlock->state = -1;
|
||||
|
||||
/* see the comment on this in pthread_rwlock_rdlock */
|
||||
_pthread_mutex_unlock(&prwlock->lock);
|
||||
|
||||
return (ret);
|
||||
}
|
||||
|
||||
@ -415,3 +439,62 @@ _pthread_rwlock_timedwrlock (pthread_rwlock_t *rwlock,
|
||||
{
|
||||
return (rwlock_wrlock_common (rwlock, abstime));
|
||||
}
|
||||
|
||||
int
|
||||
_pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
|
||||
{
|
||||
struct pthread *curthread = _get_curthread();
|
||||
pthread_rwlock_t prwlock;
|
||||
int32_t state;
|
||||
|
||||
if (__predict_false(rwlock == NULL))
|
||||
return (EINVAL);
|
||||
|
||||
prwlock = *rwlock;
|
||||
|
||||
if (__predict_false(prwlock == NULL))
|
||||
return (EINVAL);
|
||||
|
||||
state = prwlock->state;
|
||||
|
||||
if (state & RWLOCK_WRITE_OWNER) {
|
||||
if (__predict_false(prwlock->owner != curthread))
|
||||
return (EPERM);
|
||||
prwlock->owner = NULL;
|
||||
while (!atomic_cmpset_rel_32(&prwlock->state, state, state & ~RWLOCK_WRITE_OWNER)) {
|
||||
CPU_SPINWAIT;
|
||||
state = prwlock->state;
|
||||
}
|
||||
} else if (RWLOCK_READER_COUNT(state) != 0) {
|
||||
while (!atomic_cmpset_rel_32(&prwlock->state, state, state - 1)) {
|
||||
CPU_SPINWAIT;
|
||||
state = prwlock->state;
|
||||
if (RWLOCK_READER_COUNT(state) == 0)
|
||||
return (EPERM);
|
||||
}
|
||||
curthread->rdlock_count--;
|
||||
} else {
|
||||
return (EPERM);
|
||||
}
|
||||
|
||||
#if 0
|
||||
if (state & RWLOCK_WRITE_WAITERS) {
|
||||
_pthread_mutex_lock(&prwlock->lock);
|
||||
_pthread_cond_signal(&prwlock->write_signal);
|
||||
_pthread_mutex_unlock(&prwlock->lock);
|
||||
} else if (state & RWLOCK_READ_WAITERS) {
|
||||
_pthread_mutex_lock(&prwlock->lock);
|
||||
_pthread_cond_broadcast(&prwlock->read_signal);
|
||||
_pthread_mutex_unlock(&prwlock->lock);
|
||||
}
|
||||
#endif
|
||||
|
||||
if (state & RWLOCK_WRITE_WAITERS) {
|
||||
_pthread_mutex_lock(&prwlock->lock);
|
||||
_pthread_cond_broadcast_unlock(&prwlock->write_signal, &prwlock->lock, 0);
|
||||
} else if (state & RWLOCK_READ_WAITERS) {
|
||||
_pthread_mutex_lock(&prwlock->lock);
|
||||
_pthread_cond_broadcast_unlock(&prwlock->write_signal, &prwlock->lock, 1);
|
||||
}
|
||||
return (0);
|
||||
}
|
||||
|
Loading…
Reference in New Issue
Block a user