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PROLOG
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.
NAME
pthread_rwlock_destroy, pthread_rwlock_init — destroy and initialize a 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);
pthread_rwlock_t rwlock = PTHREAD_RWLOCK_INITIALIZER;
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.
See Section 2.9.9, Synchronization Object Copies and Alternative Mappings for further
requirements.
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.
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.
ERRORS
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.
EPERM The caller does not have the privilege to perform the operation.
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 POSIX.1‐2017, Section 3.291,
Priority Inversion.
RATIONALE
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_rwlock_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.
FUTURE DIRECTIONS
None.
SEE ALSO
pthread_rwlock_rdlock(), pthread_rwlock_timedrdlock(), pthread_rwlock_timedwrlock(),
pthread_rwlock_trywrlock(), pthread_rwlock_unlock()
The Base Definitions volume of POSIX.1‐2017, Section 3.291, Priority Inversion,
<pthread.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1-2017, Standard for Information Technology -- Portable Operating System Interface
(POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .
Any typographical or formatting errors that appear in this page are most likely to have
been introduced during the conversion of the source files to man page format. To report
such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .