pthread_rwlock_unlock()--Unlock Exclusive Write or Shared Read Lock

 #include <pthread.h>
 int pthread_rwlock_unlock(pthread_rwlock_t *rwlock);   

The pthread_rwlock_unlock() function unlocks a shared read or exclusive write lock held by the calling thread.

A thread should call pthread_rwlock_unlock() once for each time that the thread successfully called pthread_rwlock_rdlock(), pthread_rwlock_tryrdlock(), pthread_rwlock_trywrlock(), pthread_rwlock_timedrdlock_np(), or pthread_rwlock_timedwrlock_np() to acquire a shared read or exclusive write lock. For example, if a thread holds 4 shared read locks on a read/write lock object, the thread must call pthread_rwlock_unlock() 4 times before the read/write lock becomes completely unlocked.

If a thread holds both shared read and exclusive write locks for the specified read/write lock object, the exclusive write locks are unlocked first. If more than one outstanding exclusive write lock was held by the thread, a matching number of successful calls to pthread_rwlock_unlock() must be done before all write locks are unlocked. When all write locks are unlocked, subsequent calls to pthread_rwlock_unlock() unlock the shared read locks.

Authorities and Locks

For successful completion, either a shared read or exclusive write lock must be held on the read/write lock before you call pthread_rwlock_unlock().

Parameters

rwlock

(Input) The address of the read/write lock

Return Value

0

pthread_rwlock_unlock() was successful.

value

pthread_rwlock_unlock() was not successful. value is set to indicate the error condition.

Error Conditions

If pthread_rwlock_unlock() was not successful, the error condition returned usually indicates one of the following errors. Under some conditions, the value returned could indicate an error other than those listed here.

[EINVAL]

The value specified for the argument is not correct.

[EPERM]

A shared read or exclusive write lock was not held by the calling thread and could not be unlocked.

Related Information

• The <pthread.h> header file. See Header files for Pthread functions.
  
  
• pthread_rwlock_init()--Initialize Read/Write Lock
  
  
• pthread_rwlock_rdlock()--Get Shared Read Lock
  
  
• pthread_rwlock_timedrdlock_np()--Get Shared Read Lock with Time-Out
  
  
• pthread_rwlock_timedwrlock_np()--Get Exclusive Write Lock with Time-Out
  
  
• pthread_rwlock_tryrdlock()--Get Shared Read Lock with No Wait
  
  
• pthread_rwlock_trywrlock()--Get Exclusive Write Lock with No Wait
  
  
• pthread_rwlock_wrlock()--Get Exclusive Write Lock

Example

See any of the following examples:

• pthread_rwlock_tryrdlock()
  
  
• pthread_rwlock_trywrlock()
  
  
• pthread_rwlock_timedrdlock_np()
  
  
• pthread_rwlock_timedwrlock_np()

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