pthread_rwlock_trywrlock man page


This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

pthread_rwlock_trywrlock, pthread_rwlock_wrlock — lock a read-write lock object for writing


#include <pthread.h>

int pthread_rwlock_trywrlock(pthread_rwlock_t *rwlock);
int pthread_rwlock_wrlock(pthread_rwlock_t *rwlock);


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

The pthread_rwlock_wrlock() function shall apply 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 shall block until it can acquire the lock. The calling thread may deadlock if at the time the call is made it holds the read-write lock (whether a read or write lock).

Implementations may favor writers over readers to avoid writer starvation.

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 Value

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

If successful, the pthread_rwlock_wrlock() function shall return zero; otherwise, an error number shall be returned to indicate the error.


The pthread_rwlock_trywrlock() function shall fail if:

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

The pthread_rwlock_wrlock() function may fail if:

A deadlock condition was detected or the current thread already owns the read-write lock for writing or reading.

These functions shall not return an error code of [EINTR].

The following sections are informative.

Application Usage

Applications using these functions may be subject to priority inversion, as discussed in the Base Definitions volume of POSIX.1‐2008, Section 3.287, Priority Inversion.


If an implementation detects that the value specified by the rwlock argument to pthread_rwlock_trywrlock() or pthread_rwlock_wrlock() does not refer to an initialized read-write lock object, it is recommended that the function should fail and report an [EINVAL] error.

See Also

pthread_rwlock_destroy(), pthread_rwlock_rdlock(), pthread_rwlock_timedrdlock(), pthread_rwlock_timedwrlock(), pthread_rwlock_unlock()

The Base Definitions volume of POSIX.1‐2008, Section 3.287, Priority Inversion, Section 4.11, Memory Synchronization, <pthread.h>