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Pthread Library
HP-UX 11i Version 3: February 2007

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pthread_rwlock_wrlock(), pthread_rwlock_trywrlock() — lock or attempt to lock a read-write lock for writing


#include <pthread.h>

int pthread_rwlock_wrlock( pthread_rwlock_t *rwlock );

int pthread_rwlock_trywrlock( pthread_rwlock_t *rwlock );



Pointer to the read-write lock to be locked for writing.


The pthread_rwlock_wrlock() function applies a write lock to the read-write lock object 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 (that is, it does not return from the pthread_rwlock_wrlock() call) until it can acquire the lock. Results are undefined if the calling thread holds the read-write lock (whether a read or a write lock) at the time the call is made.

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

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, upon return from the signal handler, the thread shall resume waiting for the read-write lock as if it was not interrupted.


Upon successful completion, pthread_rwlock_wrlock() and pthread_rwlock_trywrlock() return zero. Otherwise, an error number is returned to indicate the error (the errno variable is not set).


If any of the following occur, the pthread_rwlock_trywrlock() function returns the corresponding error number:


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

For each of the following conditions, if the condition is detected, the pthread_rwlock_wrlock() and pthread_rwlock_trywrlock() functions return the corresponding error number:


The value specified by rwlock does not refer to an initialized read-write lock.


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


pthread_rwlock_wrlock() and pthread_rwlock_trywrlock() were developed by X/Open.


pthread_rwlock_init(3T), pthread_rwlock_destroy(3T), pthread_rwlock_tryrdlock(3T), pthread_rwlock_rdlock(3T), pthread_rwlock_unlock(3T).


pthread_rwlock_wrlock(): X/Open. pthread_rwlock_trywrlock(): X/Open.

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