NAME

pvm_precv − Receive a message directly into a buffer. 
 

SYNOPSIS

Cint info = pvm_precv( int tid, int msgtag, char ∗buf,
                      int len, int datatype, int ∗atid,
                      int ∗atag, int ∗alen )
 
Fortrancall pvmfprecv( tid, msgtag, buf, len, datatype,
                        atid, atag, alen, info )

PARAMETERS

tidInteger task identifier of sending process (to match). 

msgtagInteger message tag (to match).  msgtag should be >= 0. 

bufPointer to a buffer to receive into. 

lenLength of buffer (in multiple of data type size). 

datatypeType of data to which buf points (see below). 

atidReturns actual TID of sender. 

atagReturns actual message tag. 

alenReturns actual message length. 

infoReturns 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]

datatypeData Type
PVM_STRstring
PVM_BYTEbyte
PVM_SHORTshort
PVM_INTint
PVM_FLOATreal
PVM_CPLXcomplex
PVM_DOUBLEdouble
PVM_DCPLXdouble complex
PVM_LONGlong integer
PVM_USHORTunsigned short int
PVM_UINTunsigned int
PVM_ULONGunsigned 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

PvmBadParam
giving an invalid tid, msgtag, or datatype.

PvmSysErr
pvmd not responding.

SEE ALSO

pvm_psend(3PVM), pvm_recv(3PVM)

  —  15 March, 1994