PRECV (3)
Receive a message directly into a buffer.
SYNOPSIS
B
C int info = pvm_precv( int tid, int msgtag, char *buf,
int len, int datatype, int *atid,
int *atag, int *alen )
Fortran call pvmfprecv( tid, msgtag, buf, len, datatype,
atid, atag, alen, info )
PARAMETERS
Integer task identifier of sending process (to match).
Integer message tag (to match).
msgtag should be >= 0.
Pointer to a buffer to receive into.
Length of buffer (in multiple of data type size).
Type of data to which buf points (see below).
Returns actual TID of sender.
Returns actual message tag.
Returns actual message length.
Returns PvmOk on success.
Values less than zero indicate an error.
DESCRIPTION
The routine
pvm_precv
blocks the process until a message with label
msgtag
has arrived from tid.
pvm_precv then places the contents of the message in the supplied buffer,
buf,
up to a maximum length of len * (size of data type).
pvm_precv can receive messages sent by pvm_psend, pvm_send,
pvm_mcast, or pvm_bcast.
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_precv will accept a message from any process
which has a matching msgtag.
If msgtag = -1 and tid is defined by the user,
then pvm_precv will accept any message that is sent from process tid.
If tid = -1 and msgtag = -1,
then pvm_precv will accept any message from any process.
In C the datatype parameter must be one of the following,
depending on the type of data to be unpacked:
[Version 3.3.0 - This parameter only determines message length,
not data conversion. It only unpacks raw bytes]
4 16
datatype Data Type
PVM_STR string
PVM_BYTE byte
PVM_SHORT short
PVM_INT int
PVM_FLOAT real
PVM_CPLX complex
PVM_DOUBLE double
PVM_DCPLX double complex
PVM_LONG long integer
PVM_USHORT unsigned short int
PVM_UINT unsigned int
PVM_ULONG unsigned long int
In Fortran the same data types specified for unpack should be used.
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.
If pvm_precv is successful,
info
will be = 0.
If some error occurs then info will be < 0.
pvm_precv is blocking which means the routine waits until a message
matching the user specified tid and msgtag arrives at the
local pvmd.
If the message has already arrived then pvm_precv
returns immediately with the message.
pvm_precv does not affect the state of the current receive message buffer
(created by the other receive functions).
WARNINGS
In some versions of PVM (CM5, I860 and PGON),
messages sent using pvm_psend must be received only by pvm_precv,
likewise those sent with pvm_send
must be received by pvm_recv, pvm_nrecv or pvm_trecv.
pvm_psend is not compatible with pvm_recv
(nor pvm_send with pvm_precv).
In addition, pvm_probe is not interoperable with pvm_psend.
This problem occurs
because nonstandard message headers are used for efficiency
in the pvm_psend function.
In the generic Unix version of PVM,
the calls are fully interoperable.
The message tag space is shared between pvm_send and pvm_psend,
so you must be careful to avoid selecting the wrong message
(for example by using a wildcard to match the message).
EXAMPLES
C:
info = pvm_precv( tid, msgtag, array, cnt, PVM_FLOAT,
&src, &rtag, &rlen );
Fortran:
CALL PVMFPRECV( -1, 4, BUF, CNT, REAL4,
> SRC, RTAG, RCNT, INFO )
ERRORS
These error conditions can be returned by
pvm_precv
giving an invalid tid, msgtag, or datatype.
SEE ALSO
pvm_psend(3PVM) pvm_recv(3PVM)
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