.\" $Id: pvm_probe.3,v 1.1 1996/09/23 22:05:53 pvmsrc Exp $
.TH PROBE 3PVM "30 August, 1993" "" "PVM Version 3.4"
.SH NAME
pvm_probe \- Check if message has arrived.

.SH SYNOPSIS
.nf
.ft B
C	int bufid = pvm_probe( int tid, int msgtag )
.br

Fortran	call pvmfprobe( tid, msgtag, bufid )
.fi

.SH PARAMETERS
.IP tid 0.8i
Integer task identifier of sending process supplied by the user.
.br
.IP msgtag
Integer message tag supplied by the user.
msgtag should be >= 0.
.br
.IP bufid
Integer returning the value of the new active receive buffer
identifier.  Values less than zero indicate an error.

.SH DESCRIPTION
The routine
.I pvm_probe
checks to see if a message with label
.I msgtag
has arrived from
.I tid.
If a matching message has arrived pvm_probe
returns a buffer identifier in
.I bufid.
This
.I bufid
can be used with pvm_bufinfo
to determine information about the message such as
its source and length.
.PP
If the requested message has not arrived, then pvm_probe
returns with a 0 in
.I bufid.
If some error occurs
.I bufid
will be < 0.
.PP
A -1 in
.I msgtag
or
.I tid
matches anything.
This allows the user the following options.
If tid = -1 and msgtag is defined by the user,
then pvm_probe will accept a message from any process
which has a matching msgtag.
If msgtag = -1 and tid is defined by the user,
then pvm_probe will accept any message that is sent from process tid.
If tid = -1 and msgtag = -1,
then pvm_probe will accept any message from any process.
.PP
pvm_probe can be called multiple times to check if a given
message has arrived yet. After the message has arrived,
pvm_recv must be called before the message can be unpacked
into the user's memory using the unpack routines.

.SH EXAMPLES
.nf
C:
	tid = pvm_parent();
	msgtag = 4 ;
	arrived = pvm_probe( tid, msgtag );
	if ( arrived )
		info = pvm_bufinfo( arrived, &len, &tag, &tid );
	else
		/* go do other computing */
.sp
Fortran:
	CALL PVMFPROBE( -1, 4, ARRIVED )
	IF ( ARRIVED .GT. 0 ) THEN
		CALL PVMFBUFINFO( ARRIVED, LEN, TAG, TID, INFO )
	ELSE
*		GO DO USEFUL WORK
	ENDIF
.fi

.SH ERRORS
These error conditions can be returned by
.I pvm_probe.
.IP PvmBadParam
giving an invalid tid value or msgtag.
.IP PvmSysErr
pvmd not responding.
.PP
.SH SEE ALSO
pvm_bufinfo(3PVM),
pvm_getminfo(3PVM),
pvm_nrecv(3PVM),
pvm_recv(3PVM),
pvm_unpack(3PVM)