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 abs_timeout);

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 abs_timeout passes, as measured by
       the clock on which timeouts are based  (that  is,  when  the  value  of  that  clock  equals  or  exceeds
       abs_timeout), or if the absolute time specified by abs_timeout has already been passed at the time of the
       call.

       If the Timers option is supported, the timeout shall be based on the CLOCK_REALTIME clock.  If the Timers
       option  is  not  supported,  the  timeout  shall  be  based on the system clock as returned by the time()
       function. The resolution of the timeout shall be the resolution of the clock on which it  is  based.  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 abs_timeout 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
              The calling thread already holds a write lock on rwlock.

       EINVAL The value specified by rwlock does not refer to an initialized  read-write  lock  object,  or  the
              abs_timeout 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 IEEE Std 1003.1-2001, Section 3.285, Priority Inversion.

       The pthread_rwlock_timedrdlock() function is part of the Threads and Timeouts options  and  need  not  be
       provided on all implementations.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       pthread_rwlock_destroy()      ,      pthread_rwlock_rdlock()     ,     pthread_rwlock_timedwrlock()     ,
       pthread_rwlock_tryrdlock()     ,     pthread_rwlock_trywrlock()     ,      pthread_rwlock_unlock()      ,
       pthread_rwlock_wrlock() , the Base Definitions volume of IEEE Std 1003.1-2001, <pthread.h>, <time.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
       Standard  for  Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003 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 .

IEEE/The Open Group                                   2003                         PTHREAD_RWLOCK_TIMEDRDLOCK(P)