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 .