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 .