pthread_rwlock_rdlock(3)
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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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