PRECV(3PVM) PVM Version 3.4 PRECV(3PVM)NAMEpvm_precv - Receive a message directly into a buffer.
SYNOPSIS
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
tid Integer task identifier of sending process (to match).
msgtag Integer message tag (to match). msgtag should be >= 0.
buf Pointer to a buffer to receive into.
len Length of buffer (in multiple of data type size).
datatype
Type of data to which buf points (see below).
atid Returns actual TID of sender.
atag Returns actual message tag.
alen Returns actual message length.
info 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 fol‐
lowing 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]
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, mes‐
sage A will arrive at task 2 before message B. Moreover, if both mes‐
sages 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 buf‐
fer (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
PvmBadParam
giving an invalid tid, msgtag, or datatype.
PvmSysErr
pvmd not responding.
SEE ALSOpvm_psend(3PVM), pvm_recv(3PVM)
15 March, 1994 PRECV(3PVM)
