NAME

pvm_nrecv − Non-blocking receive. 
 

SYNOPSIS

Cint bufid = pvm_nrecv( int tid, int msgtag )
 
Fortrancall pvmfnrecv( tid, msgtag, bufid )

PARAMETERS

tidInteger task identifier of sending process supplied by the user. 

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

bufidInteger 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_recv(3PVM), pvm_unpack(3PVM), pvm_send(3PVM), pvm_mcast(3PVM)

  —  30 August, 1993