---
name: "pvm_precv"
section: "3"
platform: "linux"
package: "pvm-dev"
version: "3.4.2-8"
release: "Debian 3.0 (Woody)"
platforms: ["linux"]
url: "https://new.carta.tech/pvm_precv"
---

# pvm\_precv(3)

Receive a message directly into a buffer.

## 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).**\

- 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 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).

## 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)