NRECV (3)
Non-blocking receive.
SYNOPSIS
B
C int bufid = pvm_nrecv( int tid, int msgtag )
Fortran call pvmfnrecv( tid, msgtag, bufid )
PARAMETERS
Integer task identifier of sending process supplied by the user.
Integer message tag supplied by the user.
msgtag should be >= 0.
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.
giving an invalid tid value or msgtag.
SEE ALSO
pvm_bufinfo(3PVM) pvm_getminfo(3PVM) pvm_recv(3PVM) pvm_unpack(3PVM) pvm_send(3PVM) pvm_mcast(3PVM)
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