NRECV(3PVM)

NAME
pvm_nrecv - Non-blocking receive.

SYNOPSIS
C    int bufid = pvm_nrecv( int tid, int msgtag )
Fortran    call pvmfnrecv( tid, msgtag, bufid )

PARAMETERS

tid Integer task identifier of sending process supplied by the user.

msgtag
    Integer message tag supplied by the user. msgtag should be >= 0.

bufid
    Integer returning the value of the new active receive buffer identifier. Values less than zero indicate an error.

DISCUSSION
The routine pvm_nrecv checks to see if a message with label msgtag has arrived from tid. and also clears the current receive buffer if any, If a matching message has arrived pvm_nrecv immediately places the message in a new active receive buffer, and returns the buffer identifier in bufid.

If the requested message has not arrived, then pvm_nrecv immediately returns with a 0 in bufid. If some error occurs bufid will be < 0.

A -1 in msgtag or tid matches anything. This allows the user the following options. If tid = -1 and msgtag is defined by the user, then pvm_nrecv will accept a message from any process which has a matching msgtag. If msgtag = -1 and tid is defined by the user, then pvm_nrecv will accept any message that is sent from process tid. If tid = -1 and msgtag = -1, then pvm_nrecv will accept any message from any process.

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.

pvm_nrecv is non-blocking in the sense that the routine always returns immediately either with the message or with the information that the message has not arrived at the local pvmd yet. pvm_nrecv can be called multiple times to check if a given message has arrived yet. In addition the blocking receive pvm_recv can be called for the same message if the application runs out of work it could do before the data arrives.

If pvm_nrecv returns with the message, then the data in the message can be unpacked into the user's memory using the unpack routines.

EXAMPLES
C:
	tid = pvm_parent();
	msgtag = 4 ;
	arrived = pvm_nrecv( tid, msgtag );
	if ( arrived > 0)
		info = pvm_upkint( tid_array, 10, 1 );
	else
		/* go do other computing */

Fortran:
	CALL PVMFNRECV( -1, 4, ARRIVED )
	IF ( ARRIVED .gt. 0 ) THEN
	   CALL PVMFUNPACK( INTEGER4, TIDS, 25, 1, INFO )
	   CALL PVMFUNPACK( REAL8, MATRIX, 100, 100, INFO )
	ELSE
*	   GO DO USEFUL WORK
	ENDIF

ERRORS
These error conditions can be returned by pvm_nrecv.
	PvmBadParam	giving an invalid tid value or msgtag.
	PvmSysErr	pvmd not responding.

SEE ALSO
recv(3PVM), unpack(3PVM), send(3PVM), mcast(3PVM)