[MPICH] Variable length size of message

[Jarosław Bułat]

Hello!

I would like to send variable length size message between two processes.
Suppose maximal length of the message is known as MAXLEN. Can I do that
in the following way?:

receiver: 
char dIn[ msgSIZE ];
MPI_Irecv( dIn, MAXLEN, MPI_CHAR, rankSend, tagPING, MPI_COMM_WORLD,
req );

sender:
char dOut[ msgSIZE ];
int vsize = 1024;
MPI_Send( dOut, vsize, MPI_CHAR, rankRec, tagPING, MPI_COMM_WORLD );

Suppose first 4 bytes of dOut consists of length of the message. In that
way one can determine real length of message in receiver.

I've tested such a configuration and it's working. My question is: Is it
legal/supported? or is it working accidentally?


Jarek!