pthread_rwlock_trywrlock, pthread_rwlock_wrlock - lock a read-write lock object for writing
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 shall acquire the write lock if no thread (reader or writer) holds the read-write lock rwlock. Otherwise, if another thread holds the read-write lock rwlock, the calling thread shall block until it can acquire the lock. If a deadlock condition occurs or the calling thread already owns the read-write lock for writing or reading, the call shall either deadlock or return [EDEADLK].
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.
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].
Applications using these functions may be subject to priority inversion, as discussed in XBD 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.
pthread_rwlock_destroy, pthread_rwlock_rdlock, pthread_rwlock_timedrdlock, pthread_rwlock_timedwrlock, pthread_rwlock_unlock
XBD Priority Inversion, Memory Synchronization, <pthread.h>
First released in Issue 5.
The following changes are made for alignment with IEEE Std 1003.1j-2000:
The margin code in the SYNOPSIS is changed to THR to indicate that the functionality is now part of the Threads option (previously it was part of the Read-Write Locks option in IEEE Std 1003.1j-2000 and also part of the XSI extension).
The [EDEADLK] error is deleted as a pthread_rwlock_trywrlock() error.
The SEE ALSO section is updated.
IEEE Std 1003.1-2001/Cor 2-2004, item XSH/TC2/D6/104 is applied, updating the ERRORS section so that the [EDEADLK] error includes detection of a deadlock condition.
The pthread_rwlock_trywrlock() and pthread_rwlock_wrlock() functions are moved from the Threads option to the Base.
The [EINVAL] error for an uninitialized read-write lock object is removed; this condition results in undefined behavior.
POSIX.1-2008, Technical Corrigendum 2, XSH/TC2-2008/0290  and XSH/TC2-2008/0291  are applied.
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