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 .