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_trywrlock, pthread_rwlock_wrlock — lock a read-write lock object for writing

SYNOPSIS

       #include <pthread.h>

       int pthread_rwlock_trywrlock(pthread_rwlock_t *rwlock);
       int pthread_rwlock_wrlock(pthread_rwlock_t *rwlock);

DESCRIPTION

       The  pthread_rwlock_trywrlock()  function  shall  apply  a  write  lock  like the pthread_rwlock_wrlock()
       function, with the exception that the function shall fail if  any  thread  currently  holds  rwlock  (for
       reading or writing).

       The  pthread_rwlock_wrlock()  function  shall  apply  a  write  lock to the read-write lock referenced by
       rwlock.  The calling thread shall acquire the write lock if no thread (reader or writer) holds the  read-
       write  lock  rwlock.   Otherwise,  if another thread holds the read-write lock rwlock, the calling thread
       shall block until it can acquire the lock.  If a deadlock condition occurs or the calling thread  already
       owns the read-write lock for writing or reading, the call shall either deadlock or return [EDEADLK].

       Results are undefined if any of these functions are called with an uninitialized read-write lock.

       If  a  signal  is  delivered  to a thread waiting for a read-write lock for writing, upon return from the
       signal handler the thread resumes waiting  for  the  read-write  lock  for  writing  as  if  it  was  not
       interrupted.

RETURN VALUE

       The  pthread_rwlock_trywrlock() function shall return zero if the lock for writing on the read-write lock
       object referenced by rwlock is acquired. Otherwise, an error number shall be  returned  to  indicate  the
       error.

       If  successful,  the pthread_rwlock_wrlock() function shall return zero; otherwise, an error number shall
       be returned to indicate the error.

ERRORS

       The pthread_rwlock_trywrlock() function shall fail if:

       EBUSY  The read-write lock could not be acquired for writing because it was already locked for reading or
              writing.

       The pthread_rwlock_wrlock() function may fail if:

       EDEADLK
              A deadlock condition was detected or the current thread  already  owns  the  read-write  lock  for
              writing or reading.

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

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       Applications  using  these  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_trywrlock()  or  pthread_rwlock_wrlock()  does not refer to an initialized read-write lock
       object, it is recommended that the function should fail and report an [EINVAL] error.

FUTURE DIRECTIONS

       None.

SEE ALSO

       pthread_rwlock_destroy(), pthread_rwlock_rdlock(), pthread_rwlock_timedrdlock(),
       pthread_rwlock_timedwrlock(), pthread_rwlock_unlock()

       The Base Definitions volume of POSIX.1‐2017, Section 3.291,  Priority  Inversion,  Section  4.12,  Memory
       Synchronization, <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 .

IEEE/The Open Group                                   2017                      PTHREAD_RWLOCK_TRYWRLOCK(3POSIX)