GETFDS(3PVM)							 GETFDS(3PVM)

NAME
  pvm_getfds - Get file	descriptors in use by PVM.

SYNOPSIS
  C	  int nfds = pvm_getfds( int **fds )

  Fortran Not Available

PARAMETERS

  fds	  Returns integer array	of file	descriptors.

DISCUSSION
  A PVM	task uses sockets to communicate between libpvm	and other tasks	or
  the pvmd.  It	is sometimes useful to know the	file descriptor	numbers	of
  the sockets in order to wait from input from either PVM messages or an
  external source.  For	example, the PVM console waits on both keyboard	input
  and notify messages.	Input can be multiplexed by polling all	sources, but
  this wastes cpu cycles.  Instead, the	select() system	call can be used to
  wait until one or more sources of input are ready.

  If it	completes successfully,	pvm_getfds returns the number of sockets in
  use, and the file descriptor numbers in an array (allocated and freed	by
  libpvm).  At least one socket	always exists (from task to pvmd), and its
  descriptor is	always fds[0].	The number of sockets varies as	direct routes
  are established to other tasks.

  It can be difficult to track the set of file descriptors if direct routing
  is enabled, because routes are created as messages are either	sent or
  received.  The simplest approach is to disable direct	routing.

  When select returns with a PVM file descriptor ready,	a complete message
  may be ready to be received, or instead only a fragment may be waiting.
  pvm_nrecv or pvm_probe should	be used	test without blocking.

EXAMPLES
  The following	program	fragment waits until either keyboard input is avail-
  able,	or a PVM message has arrived.

	  int *d;
	  fd_set r;

	  pvm_setopt(PvmRoute, PvmDontRoute);
	  pvm_getfds(&d);

	  FD_ZERO(&r);
	  FD_SET(0, &r);
	  FD_SET(d[0], &r);
	  while	(1) {
		  if (select(d[0] + 1, &r, (fd_set*)0, (fd_set*)0,
			     (struct timeval*)0) > 0) {
			  if (FD_ISSET(0, &r))
				  ...	 /* read keyboard input	*/
			  if (FD_ISSET(d[0], &r) && pvm_nrecv(-1, -1) >	0)
				  ...	 /* got	a PVM message */
		  }
	  }

ERRORS
  The following	error condition	can be returned	by pvm_getfds:
       PvmSysErr      pvmd not responding.

RESTRICTIONS
  pvm_getfds is	only availble when running PVM on a Unix or similar system.

SEE ALSO
  pvm_notify(3PVM), pvm_trecv(3PVM)