This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
pthread_rwlock_destroy, pthread_rwlock_init — destroy and initialize a read-write lock object
int pthread_rwlock_destroy(pthread_rwlock_t * rwlock);
int pthread_rwlock_init(pthread_rwlock_t *restrict rwlock, const pthread_rwlockattr_t *restrict attr);
pthread_rwlock_t rwlock = PTHREAD_RWLOCK_INITIALIZER;
The pthread_rwlock_destroy() function shall destroy the read-write lock object referenced by rwlock and release any resources used by the lock. The effect of subsequent use of the lock is undefined until the lock is reinitialized 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 behavior.
The pthread_rwlock_init() function shall allocate any resources required to use the read-write lock referenced by rwlock and initializes the lock to an unlocked state with attributes referenced by attr. If attr is NULL, the default read-write lock attributes shall be 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 reinitialized. 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 shall not be initialized and the contents of rwlock are undefined.
Only the object referenced by rwlock may be used for performing synchronization. The result of referring to copies of that object in calls to pthread_rwlock_destroy(), pthread_rwlock_rdlock(), pthread_rwlock_timedrdlock(), pthread_rwlock_timedwrlock(), pthread_rwlock_tryrdlock(), pthread_rwlock_trywrlock(), pthread_rwlock_unlock(), or pthread_rwlock_wrlock() is undefined.
In cases where default read-write lock attributes are appropriate, the macro PTHREAD_RWLOCK_INITIALIZER can be used to initialize read-write locks. The effect shall be equivalent to dynamic initialization by a call to pthread_rwlock_init() with the attr parameter specified as NULL, except that no error checks are performed.
The behavior is undefined if the value specified by the attr argument to pthread_rwlock_init() does not refer to an initialized read-write lock attributes object.
If successful, the pthread_rwlock_destroy() and pthread_rwlock_init() functions shall return zero; otherwise, an error number shall be returned to indicate the error.
The pthread_rwlock_init() function shall fail if:
- The system lacked the necessary resources (other than memory) to initialize another read-write lock.
- Insufficient memory exists to initialize the read-write lock.
These functions shall not return an error code of [EINTR].
The following sections are informative.
Applications using these and related read-write lock functions may be subject to priority inversion, as discussed in the Base Definitions volume of POSIX.1‐2008, Section 3.287, Priority Inversion.
If an implementation detects that the value specified by the rwlock argument to pthread_rwlock_destroy() does not refer to an initialized read-write lock object, it is recommended that the function should fail and report an [EINVAL] error.
If an implementation detects that the value specified by the attr argument to pthread_rwlockr_init() does not refer to an initialized read-write lock attributes object, it is recommended that the function should fail and report an [EINVAL] error.
If an implementation detects that the value specified by the rwlock argument to pthread_rwlock_destroy() or pthread_rwlock_init() refers to a locked read-write lock object, or detects that the value specified by the rwlock argument to pthread_rwlock_init() refers to an already initialized read-write lock object, it is recommended that the function should fail and report an [EBUSY] error.
pthread_rwlock_rdlock(), pthread_rwlock_timedrdlock(), pthread_rwlock_timedwrlock(), pthread_rwlock_trywrlock(), pthread_rwlock_unlock()
The Base Definitions volume of POSIX.1‐2008, Section 3.287, Priority Inversion, <pthread.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html .
- The caller does not have the privilege to perform the operation.
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