PTHREAD_RWLOCK_RDLOCK(3) | Library Functions Manual | PTHREAD_RWLOCK_RDLOCK(3) |
pthread_rwlock_rdlock
,
pthread_rwlock_tryrdlock
—
acquire a read/write lock for reading
#include
<pthread.h>
int
pthread_rwlock_rdlock
(pthread_rwlock_t
*lock);
int
pthread_rwlock_tryrdlock
(pthread_rwlock_t
*lock);
The
pthread_rwlock_rdlock
()
function acquires a read lock on lock provided that
lock is not presently held for writing and no writer
threads are presently blocked on the lock. If the read lock cannot be
immediately acquired, the calling thread blocks until it can acquire the
lock.
The
pthread_rwlock_tryrdlock
()
function performs the same action, but does not block if the lock cannot be
immediately obtained (i.e., the lock is held for writing or there are
waiting writers).
A thread may hold multiple concurrent
read locks. If so,
pthread_rwlock_unlock
()
must be called once for each lock obtained.
The results of acquiring a read lock while the calling thread holds a write lock are undefined.
To prevent writer starvation, writers are favored over readers.
If successful, the pthread_rwlock_rdlock
()
and pthread_rwlock_tryrdlock
() functions will return
zero. Otherwise an error number will be returned to indicate the error.
The pthread_rwlock_tryrdlock
() function
will fail if:
EBUSY
]The pthread_rwlock_rdlock
() and
pthread_rwlock_tryrdlock
() functions may fail
if:
EAGAIN
]EDEADLK
]EINVAL
]ENOMEM
]pthread_rwlock_init(3), pthread_rwlock_trywrlock(3), pthread_rwlock_unlock(3), pthread_rwlock_wrlock(3)
The pthread_rwlock_rdlock
() and
pthread_rwlock_tryrdlock
() functions are expected to
conform to Version 2 of the Single UNIX
Specification (“SUSv2”).
The pthread_rwlock_rdlock
() function first
appeared in FreeBSD 3.0.
August 4, 1998 | macOS 14.6 |