man pages section 3: Basic Library Functions

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Updated: July 2014



pthread_rwlock_init, pthread_rwlock_destroy - initialize or destroy read-write lock object


cc –mt [ flag... ] file... [ library... ]
#include <pthread.h>

int pthread_rwlock_init(pthread_rwlock_t *restrict rwlock,
     const pthread_rwlockattr_t *restrict attr);
int pthread_rwlock_destroy(pthread_rwlock_t **rwlock);
pthread_rwlock_t rwlock=PTHREAD_RWLOCK_INITIALIZER;


The pthread_rwlock_init() function initializes the read-write lock referenced by rwlock with the attributes referenced by attr. If attr is NULL, the default read-write lock attributes are used; the effect is the same as passing the address of a default read-write lock attributes object. Once initialized, the lock can be used any number of times without being re-initialized. Upon successful initialization, the state of the read-write lock becomes initialized and unlocked. Results are undefined if pthread_rwlock_init() is called specifying an already initialized read-write lock. Results are undefined if a read-write lock is used without first being initialized.

If the pthread_rwlock_init() function fails, rwlock is not initialized and the contents of rwlock are undefined.

The pthread_rwlock_destroy() function destroys the read-write lock object referenced by rwlock and releases any resources used by the lock. The effect of subsequent use of the lock is undefined until the lock is re-initialized by another call to pthread_rwlock_init(). An implementation may cause pthread_rwlock_destroy() to set the object referenced by rwlock to an invalid value. Results are undefined if pthread_rwlock_destroy() is called when any thread holds rwlock. Attempting to destroy an uninitialized read-write lock results in undefined behaviour. A destroyed read-write lock object can be re-initialized using pthread_rwlock_init(); the results of otherwise referencing the read-write lock object after it has been destroyed are undefined.

In cases where default read-write lock attributes are appropriate, the macro PTHREAD_RWLOCK_INITIALIZER can be used to initialize read-write locks that are statically allocated. The effect is equivalent to dynamic initialization by a call to pthread_rwlock_init() with the parameter attr specified as NULL, except that no error checks are performed.

Return Values

If successful, the pthread_rwlock_init() and pthread_rwlock_destroy() functions return 0. Otherwise, an error number is returned to indicate the error.


The pthread_rwlock_init() and pthread_rwlock_destroy() functions will fail if:


The value specified by attr is invalid.


The value specified by rwlock is invalid.


See attributes(5) for descriptions of the following attributes:

Interface Stability

See also

pthread_rwlock_rdlock(3C), pthread_rwlock_unlock(3C), pthread_rwlock_wrlock(3C), pthread_rwlockattr_init(3C), attributes(5), standards(5)