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PRECV(3PVM)			 PVM Version 3.4		     PRECV(3PVM)

NAME
     pvm_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).

     datatypeType 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 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 ms-
     gtag  =  -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  deter-
     mines 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 match-
     ing 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 compati-
     ble 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  effi-
     ciency  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 		     PRECV(3PVM)

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