pthread_rwlock_wrlock

, pthread_rwlock_trywrlock

- lock or attempt to lock read-write lock object for writing

Synopsis

cc –mt [ flag... ] file... [ library... ]
#include <pthread.h>

int pthread_rwlock_wrlock(pthread_rwlock_t *rwlock);

int pthread_rwlock_trywrlock(pthread_rwlock_t *rwlock);

Description

The pthread_rwlock_wrlock() function applies a write lock to the read-write lock referenced by rwlock. The calling thread acquires the write lock if no other thread (reader or writer) holds the read-write lock rwlock. Otherwise, the thread blocks until it can acquire the lock.

The pthread_rwlock_trywrlock() function applies a write lock like the pthread_rwlock_wrlock() function, with the exception that the function fails if any thread currently holds rwlock (for reading or writing).

Writers are favored over readers of the same priority to avoid writer starvation. See pthread_rwlock_rdlock(3C).

Results are undefined if any of these functions are called with an uninitialized read-write lock.

If a signal is delivered to a thread waiting for a read-write lock for writing, upon return from the signal handler the thread resumes waiting for the read-write lock for writing as if it was not interrupted.

Return Values

If successful, the pthread_rwlock_wrlock() function returns 0. Otherwise, an error number is returned to indicate the error.

The pthread_rwlock_trywrlock() function returns 0 if the lock for writing on the read-write lock object referenced by rwlock is acquired. Otherwise an error number is returned to indicate the error.

Errors

The pthread_rwlock_wrlock() function will fail if:

EDEADLK

The current thread already owns the read-write lock for writing or reading.

The pthread_rwlock_trywrlock() function will fail if:

EBUSY

The read-write lock could not be acquired for writing because it was already locked for reading or writing.

Attributes

See attributes(5) for descriptions of the following attributes:

See Also

pthread_rwlock_init(3C), pthread_rwlock_unlock(3C), pthread_rwlockattr_init(3C), pthread_rwlock_rdlock(3C), attributes(5), standards(5)