.\" $Id: pvm_recv.3,v 1.1 1996/09/23 22:05:59 pvmsrc Exp $
.TH RECV 3PVM "30 August, 1993" "" "PVM Version 3.4"
.SH NAME
pvm_recv \- Receive a message.

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

Fortran	call pvmfrecv( 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 returns the value of the new active receive buffer identifier.
Values less than zero indicate an error.

.SH DESCRIPTION
The routine
.I pvm_recv
blocks the process until a message with label
.I msgtag
has arrived from
.I tid.
pvm_recv then places the message in a new \fIactive\fR receive buffer,
which also clears the current receive buffer.
.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_recv will accept a message from any process
which has a matching msgtag.
If msgtag = -1 and tid is defined by the user,
then pvm_recv will accept any message that is sent from process tid.
If tid = -1 and msgtag = -1,
then pvm_recv will accept any message from any process.
.PP
The PVM model guarantees the following about message order.
If task 1 sends message A to task 2, then task 1 sends message B to task 2,
message A will arrive at task 2 before message B.
Moreover, if both messages arrive before task 2 does a receive,
then a wildcard receive will always return message A.
.PP
If pvm_recv is successful,
.I bufid
will be the value of the new active receive buffer identifier.
If some error occurs then
.I bufid
will be < 0.
.PP
pvm_recv is blocking which means the routine waits until a message
matching the user specified tid and msgtag values arrives at the
local pvmd. If the message has already arrived then pvm_recv
returns immediately with the message.
.PP
Once pvm_recv returns, the data in the message can be unpacked
into the user's memory using the unpack routines.

.SH EXAMPLES
.nf
C:
	tid = pvm_parent();
	msgtag = 4 ;
	bufid = pvm_recv( tid, msgtag );
	info = pvm_upkint( tid_array, 10, 1 );
	info = pvm_upkint( problem_size, 1, 1 );
	info = pvm_upkfloat( input_array, 100, 1 );
.sp
Fortran:
	CALL PVMFRECV( -1, 4, BUFID )
	CALL PVMFUNPACK( INTEGER4, TIDS, 25, 1, INFO )
	CALL PVMFUNPACK( REAL8, MATRIX, 100, 100, INFO )
.fi


.SH ERRORS
These error conditions can be returned by
.I pvm_recv
.IP PvmBadParam
giving an invalid tid value, or msgtag < -1.
.IP PvmSysErr
pvmd not responding.
.PP
.SH SEE ALSO
pvm_bufinfo(3PVM),
pvm_getminfo(3PVM),
pvm_nrecv(3PVM),
pvm_unpack(3PVM),
pvm_probe(3PVM),
pvm_send(3PVM),
pvm_mcast(3PVM)