pthread_rwlock_rdlock(3) BSD Library Functions Manual pthread_rwlock_rdlock(3)
NAME
pthread_rwlock_rdlock, pthread_rwlock_tryrdlock -- acquire a read/write
lock for reading
SYNOPSIS
#include <pthread.h>
int
pthread_rwlock_rdlock(pthread_rwlock_t *rwlock);
int
pthread_rwlock_tryrdlock(pthread_rwlock_t *rwlock);
DESCRIPTION
The pthread_rwlock_rdlock() function acquires a read lock on rwlock, pro-
vided that rwlock is not presently held for writing and no writer threads
are presently blocked on the lock. If the read lock cannot be immedi-
ately 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.
IMPLEMENTATION NOTES
To prevent writer starvation, writers are favored over readers.
RETURN VALUES
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.
SEE ALSO
pthread_rwlock_init(3), pthread_rwlock_trywrlock(3),
pthread_rwlock_unlock(3), pthread_rwlock_wrlock(3)
STANDARDS
The pthread_rwlock_rdlock() and pthread_rwlock_tryrdlock() functions are
expected to conform to Version 2 of the Single UNIX Specification
(``SUSv2'').
ERRORS
The pthread_rwlock_tryrdlock() function will fail if:
[EBUSY] The lock could not be acquired, because a writer holds
the lock or was blocked on it.
The pthread_rwlock_rdlock() and pthread_rwlock_tryrdlock() functions may
fail if:
[EAGAIN] The lock could not be acquired, because the maximum
number of read locks against lock has been exceeded.
[EDEADLK] The current thread already owns rwlock for writing.
[EINVAL] The value specified by rwlock is invalid.
[ENOMEM] Insufficient memory exists to initialize the lock
(applies to statically initialized locks only).
HISTORY
The pthread_rwlock_rdlock() function first appeared in FreeBSD 3.0.
BSD August 4, 1998 BSD
Mac OS X 10.8 - Generated Thu Aug 30 09:58:55 CDT 2012