PTHREAD_RWLOCK_TIMEDRDLOCK(P)				     POSIX Programmer's Manual				     PTHREAD_RWLOCK_TIMEDRDLOCK(P)

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 abso-
       lute 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  immedi-
       ately 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  inter-
       rupted.

       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 Technol-
       ogy -- 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)