Newsgroups: comp.parallel.mpi
From: hejc@apap2.pap.univie.ac.at
Subject: causality violation
Organization: Vienna University Computer Center
Date: 17 Dec 1996 16:50:08 GMT
Message-ID: <596j00$ubg@www.univie.ac.at>

Hi,

 I often use 'nusphot' or 'VAMPIR' to investigate my
MPI programs. Two-point communications are displayed with
arrows, pointing from the sender process to the receiver
process. 
 In some of my programs, the receiving of the message occurs
before the sending, and the arrows are pointing to the past, which
should be impossible.

 Can somebody explain me what's the origin of this 'causality
violation'?
 Is it a failure of the tracefile generation, or a failure
of the MPI program, and what conclusions can be drawn from the
occurrence of these time-reversed messages?

	Thanks in advance,

		Gerhard 

