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_timedrdlock — lock a read-write lock for reading

SYNOPSIS

       #include <pthread.h>
       #include <time.h>

       int pthread_rwlock_timedrdlock(pthread_rwlock_t *restrict rwlock,
           const struct timespec *restrict abstime);

DESCRIPTION

       The  pthread_rwlock_timedrdlock()  function shall apply a read lock to the read-write lock
       referenced by rwlock as in the pthread_rwlock_rdlock()  function.  However,  if  the  lock
       cannot  be  acquired without waiting for other threads to unlock the lock, this wait shall
       be terminated when the specified timeout  expires.  The  timeout  shall  expire  when  the
       absolute  time specified by abstime passes, as measured by the clock on which timeouts are
       based (that is, when the value of that  clock  equals  or  exceeds  abstime),  or  if  the
       absolute time specified by abstime has already been passed at the time of the call.

       The  timeout  shall  be  based on the CLOCK_REALTIME clock.  The resolution of the timeout
       shall be the resolution of the CLOCK_REALTIME clock. The timespec data type is defined  in
       the  <time.h> header. Under no circumstances shall the function fail with a timeout if the
       lock can be acquired immediately. The validity  of  the  abstime  parameter  need  not  be
       checked if the lock can be immediately acquired.

       If  a  signal that causes a signal handler to be executed is delivered to a thread blocked
       on a read-write lock via a call to  pthread_rwlock_timedrdlock(),  upon  return  from  the
       signal handler the thread shall resume waiting for the lock as if it was not interrupted.

       The  calling  thread may deadlock if at the time the call is made it holds a write lock on
       rwlock.  The results are undefined if this function is called with an uninitialized  read-
       write lock.

RETURN VALUE

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

ERRORS

       The pthread_rwlock_timedrdlock() function shall fail if:

       ETIMEDOUT
              The lock could not be acquired before the specified timeout expired.

       The pthread_rwlock_timedrdlock() function may fail if:

       EAGAIN The  read  lock  could not be acquired because the maximum number of read locks for
              lock would be exceeded.

       EDEADLK
              A deadlock condition was detected or the calling thread already holds a write  lock
              on rwlock.

       EINVAL The  abstime  nanosecond  value  is less than zero or greater than or equal to 1000
              million.

       This function shall not return an error code of [EINTR].

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       Applications using this function 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_timedrdlock() 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_timedwrlock(),
       pthread_rwlock_trywrlock(), pthread_rwlock_unlock()

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