read-write lock object
SYNOPSIS
#include <pthread.h>
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 implementa-
tion 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 unde-
fined behavior.
The pthread_rwlock_init() function shall allocate any resources
required to use the read-write lock referenced by rwlock and initial-
izes 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 num-
ber 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 ini-
tialized and the contents of rwlock are undefined.
Only the object referenced by rwlock may be used for performing syn-
chronization. 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.
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 func-
tion 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:
ENOMEM Insufficient memory exists to initialize the read-write lock.
EPERM The caller does not have the privilege to perform the operation.
The pthread_rwlock_init() function may fail if:
EBUSY The implementation has detected an attempt to reinitialize the
object referenced by rwlock, a previously initialized but not
yet destroyed read-write lock.
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() , pthread_rwlock_timedrdlock() ,
pthread_rwlock_timedwrlock() , pthread_rwlock_tryrdlock() ,
pthread_rwlock_trywrlock() , pthread_rwlock_unlock() ,
pthread_rwlock_wrlock() , 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 .
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