pvm_precv(3) Receive a message directly into a buffer.


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 )


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.


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]

    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).


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).


    info = pvm_precv( tid, msgtag, array, cnt, PVM_FLOAT,
                      &src, &rtag, &rlen );

   >                SRC, RTAG, RCNT, INFO )


These error conditions can be returned by pvm_precv
giving an invalid tid, msgtag, or datatype.
pvmd not responding.