pthread_rwlock_rdlock(3) - NetBSD Manual Pages

PTHREAD_RWLOCK_RDLOC... NetBSD Library Functions ManualPTHREAD_RWLOCK_RDLOC...


NAME
pthread_rwlock_rdlock, pthread_rwlock_timedrdlock, pthread_rwlock_tryrdlock -- acquire a read/write lock for reading
LIBRARY
POSIX Threads Library (libpthread, -lpthread)
SYNOPSIS
#include <pthread.h> int pthread_rwlock_rdlock(pthread_rwlock_t *lock); int pthread_rwlock_timedrdlock(pthread_rwlock_t * restrict lock, const struct timespec * restrict abstime); int pthread_rwlock_tryrdlock(pthread_rwlock_t *lock);
DESCRIPTION
The pthread_rwlock_rdlock() function acquires a read lock on lock pro- vided that lock 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_timedrdlock() performs the same action, but will not wait beyond abstime to obtain the lock before returning. The pthread_rwlock_tryrdlock() function performs the same action as pthread_rwlock_rdlock(), but does not block if the lock cannot be immedi- ately 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.
RETURN VALUES
If successful, the pthread_rwlock_rdlock(), pthread_rwlock_timedrdlock(), and pthread_rwlock_tryrdlock() functions will return zero. Otherwise an error number will be returned to indicate the error.
ERRORS
The pthread_rwlock_tryrdlock() function shall fail if: [EBUSY] The lock could not be acquired because a writer holds the lock or was blocked on it. The pthread_rwlock_timedrdlock() function shall fail if: [ETIMEDOUT] The time specified by abstime was reached before the lock could be obtained. The pthread_rwlock_rdlock(), pthread_rwlock_timedrdlock(), 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 lock for writing. [EINVAL] The value specified by lock is invalid.
SEE ALSO
pthread_rwlock_destroy(3), pthread_rwlock_init(3), pthread_rwlock_unlock(3), pthread_rwlock_wrlock(3)
STANDARDS
pthread_rwlock_rdlock(), pthread_rwlock_timedrdlock(), and pthread_rwlock_tryrdlock() conform to ISO/IEC 9945-1:1996 (``POSIX.1''). NetBSD 5.1 January 30, 2003 NetBSD 5.1

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