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PTHREAD_RWLOCK_WRLOCK(3) Library Functions Manual PTHREAD_RWLOCK_WRLOCK(3)

pthread_rwlock_wrlock, pthread_rwlock_timedwrlock, pthread_rwlock_trywrlock
acquire a read/write lock for writing

#include <pthread.h>
int
pthread_rwlock_wrlock(pthread_rwlock_t *lock);
int
pthread_rwlock_timedwrlock(pthread_rwlock_t *lock, const struct timespec *abstime);
int
pthread_rwlock_trywrlock(pthread_rwlock_t *lock);

The pthread_rwlock_wrlock() function blocks until a write lock can be acquired against lock.
The pthread_rwlock_timedwrlock() function performs the same action, but will not wait beyond abstime to obtain the lock before returning.
The pthread_rwlock_trywrlock() function performs the same action as pthread_rwlock_wrlock(), but does not block if the lock cannot be immediately obtained.
The results are undefined if the calling thread already holds the lock at the time the call is made.

To prevent writer starvation, writers are favored over readers.

If successful, the pthread_rwlock_wrlock(), pthread_rwlock_timedwrlock(), and pthread_rwlock_trywrlock() functions will return zero. Otherwise an error number will be returned to indicate the error.

The pthread_rwlock_trywrlock() function will fail if:
 
 
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The calling thread is not able to acquire the lock without blocking.
The pthread_rwlock_timedwrlock() function will fail if:
 
 
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The time specified by abstime was reached before the lock could be obtained.
The pthread_rwlock_wrlock(), pthread_rwlock_timedwrlock(), and pthread_rwlock_trywrlock() functions may fail if:
 
 
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The calling thread already owns the read/write lock (for reading or writing).
 
 
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The value specified by lock is invalid.
 
 
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Insufficient memory exists to initialize the lock (applies to statically initialized locks only).

pthread_rwlock_unlock(3)

The pthread_rwlock_wrlock(), pthread_rwlock_timedwrlock(), and pthread_rwlock_trywrlock() functions are expected to conform to Version 2 of the Single UNIX Specification (“SUSv2”).

The pthread_rwlock_wrlock() function first appeared in FreeBSD 3.0 and OpenBSD 2.5. The pthread_rwlock_timedwrlock() function first appeared in OpenBSD 4.8.
June 5, 2013 OpenBSD-current