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.

DESCRIPTION

       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.

RESTRICTIONS

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

EXAMPLES

       The  following  program  fragment waits until either keyboard input is available, 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.

SEE ALSO

       pvm_notify(3PVM), pvm_trecv(3PVM)

                                           22 Nov, 1994                              GETFDS(3PVM)