Ubuntu Manpage: pvm_nrecv - Non-blocking receive.

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