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)