GETFDS(3PVM) PVM Version 3.4 GETFDS(3PVM)NAMEpvm_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 num‐
bers of the sockets in order to wait from input from either PVM mes‐
sages 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 mes‐
sage 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.
RESTRICTIONSpvm_getfds is only available when running PVM on a Unix or similar sys‐
tem.
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 ALSOpvm_notify(3PVM), pvm_trecv(3PVM)
22 Nov, 1994 GETFDS(3PVM)
