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pvm_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.

DESCRIPTION

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

pvm_bufinfo(3PVM), pvm_getminfo(3PVM), pvm_recv(3PVM), pvm_unpack(3PVM), pvm_send(3PVM), pvm_mcast(3PVM)