PTHREAD_RWLOCK_RDLOCK(3) BSD Programmer's 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 provid- ed 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 ac- quired, 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 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 lock for writing. [EINVAL] The value specified by lock is invalid. [ENOMEM] Insufficient memory exists to initialize the lock (applies to statically initialized locks only).
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.
The pthread_rwlock_rdlock() function first appeared in FreeBSD 3.0 and OpenBSD 2.5. MirOS BSD #10-current August 4, 1998 1
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