#### POSIX Threads for Windows – REFERENCE - pthreads-win32

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## Name

pthread_rwlock_destroy, pthread_rwlock_init - destroy and initialize a read-write lock object

## Synopsis

#include <pthread.h>

pthread_wrlock_t rwlock = PTHREAD_RWLOCK_INITIALIZER;

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

## Description

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.

pthreads-win32 supports statically initialized rwlock objects using PTHREAD_RWLOCK_INITIALIZER. An application should still call pthread_rwlock_destroy at some point to ensure that any resources consumed by the read/write lock are released.

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.

pthreads-win32 defines _POSIX_READER_WRITER_LOCKS in pthread.h as 200112L to indicate that the reader/writer routines are implemented and may be used.

## Return Value

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 [EBUSY] and [EINVAL] error checks, if implemented, act as if they were performed immediately at the beginning of processing for the function and caused an error return prior to modifying the state of the read-write lock specified by rwlock.

## Errors

The pthread_rwlock_destroy function may fail if:

EBUSY
  The implementation has detected an attempt to destroy the object referenced by rwlock while it is locked.
EINVAL
  The value specified by rwlock is invalid.

The pthread_rwlock_init function shall fail if:

EAGAIN
  The system lacked the necessary resources (other than memory) to initialize another read-write lock.
ENOMEM
  Insufficient memory exists to initialize the read-write lock.

The pthread_rwlock_init function may fail if:

EINVAL
  The value specified by attr is invalid.

These functions shall not return an error code of [EINTR].

The following sections are informative.

## Examples

None.

## Application Usage

Applications using these and related read-write lock functions may be subject to priority inversion, as discussed in the Base Definitions volume of IEEE Std 1003.1-2001, Section 3.285, Priority Inversion.

## Rationale

None.

## Future Directions

None.

## See Also

pthread_rwlock_rdlock(3) , pthread_rwlock_timedrdlock(3) , pthread_rwlock_timedwrlock(3) , pthread_rwlock_tryrdlock(3) , pthread_rwlock_trywrlock(3) , pthread_rwlock_unlock(3) , pthread_rwlock_wrlock(3) , the Base Definitions volume of IEEE Std 1003.1-2001, <pthread.h>

## Copyright

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. 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.opengroup.org/unix/online.html .

Modified by Ross Johnson for use with pthreads-win32.

Table of Contents

- Name

- Synopsis

- Description

- Return Value

- Errors

- Examples

- Application Usage

- Rationale

- Future Directions

- See Also

- Copyright