Locks a read-write lock object for writing.
Threads Library (libpthreads.a)
#include <pthread.h>
int pthread_rwlock_wrlock (rwlock)
pthread_rwlock_t *rwlock;
int pthread_rwlock_trywrlock (rwlock)
pthread_rwlock_t *rwlock;
The pthread_rwlock_wrlock subroutine 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 (that is, 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 write lock) at the time the call is made.
Implementations are allowed to favor writers over readers to avoid writer starvation.
The pthread_rwlock_trywrlock subroutine applies a write lock like the pthread_rwlock_wrlock subroutine, 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 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.
Item | Description |
---|---|
rwlock | Specifies the read-write lock to be locked for writing. |
If successful, the pthread_rwlock_wrlock subroutine returns zero. Otherwise, an error number is returned to indicate the error.
The pthread_rwlock_trywrlock subroutine returns zero 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.
The pthread_rwlock_trywrlock subroutine will fail if:
Item | Description |
---|---|
EBUSY | The read-write lock could not be acquired for writing because it was already locked for reading or writing. |
The pthread_rwlock_wrlock and pthread_rwlock_trywrlock subroutines may fail if:
Item | Description |
---|---|
EINVAL | The value specified by rwlock does not refer to an initialized read-write lock object. |
EDEADLK | The current thread already owns the read-write lock for writing or reading. |