pthread_once(3T)														  pthread_once(3T)

NAME

       pthread_once() - call an initialization routine only once

SYNOPSIS


   Parameters
       once_control   Pointer to the once-control object associated with the one-time initialization function

       init_routine   The one-time initialization routine.  This routine is called only once, regardless of the number of times it and its associ-
		      ated once_control are passed to

DESCRIPTION

       The function guarantees that is only called one time in an application.	This function will use the once_control object to determine if has
       previously been called via

       The  first time is called with once_control and causes to be called with no arguments.  Subsequent calls to with the same once_control will
       not cause to be called again.  When returns, the caller is guaranteed that has been called (either just now or via a previous call).

       The macro is used to statically initialize a once control block.  This initialization must be done before calling

       is not a cancellation point.  However, the caller supplied may be a cancellation point.	If the thread executing is canceled, the once_con-
       trol  argument will be set to a state which indicates that has not been called yet (see pthread_cancel(3T)).  The next time the function is
       called with once_control, the function will be called.

       The behavior of is undefined if once_control has automatic storage duration or is not initialized by

RETURN VALUE

       returns returns the following values:

	      Successful completion.

	      Failure.
		     An error number is returned to indicate the error.  (The variable is not set.)

ERRORS

       The following error value is returned by if the corresponding condition is detected.

       Either	      once_control or init_routine is invalid.

EXAMPLES

       Some modules are designed for dynamic initialization, i.e., global initialization is performed when the first function  of  the	module	is
       invoked.  In a single-threaded program, this is generally implemented as follows:

	      (Rest of the code after initialization.)

       For  a  multithreaded  process, a simple initialization flag is not sufficient; the flag must be protected against modification by multiple
       threads.  Consequently, this flag has to be protected by a mutex that has to be initialized only once, and so on.  A multithreaded  program
       should use initialization similar to:

	      (Rest of the code after initialization.)

AUTHOR

       was derived from the IEEE POSIX P1003.1c standard.

SEE ALSO

       pthread_create(3T).

STANDARDS CONFORMANCE

								  Pthread Library						  pthread_once(3T)