From: Stephen Siegel <siegel@XXXXXXXXXXXX>
Date: June 9, 2006 8:05:00 PM GMT+02:00
To: William Gropp <gropp@XXXXXXXXXXX>
Cc: Rajeev Thakur <thakur@XXXXXXXXXXX>,"'Rusty Lusk'" <lusk@XXXXXXXXXXX>,"'Rob Ross'" <rross@XXXXXXXXXXX>
Subject: RE: Euro PVMMPI


Since you liked that one, here is the other error I found with
MPI-SPIN.  It's Example 2.19 ("Multiple-producer, single-consumer
code, modified to use test calls") of the same book ("MPI: The
Complete Reference, Vol. 1").  This concerns the code

for (flag=0; !flag; i=(i+1)%(size-1)) {
  MPI_Test(&(buffer[i].req), &flag, &status);
}
...
MPI_Irecv(buffer[i]...);

The code following the for loop depends upon the fact that, upon
exiting the loop, i will have the value that caused the MPI_Test
statement to set flag to true. However, i is incremented once more
before the test (!flag) is evaluated, so it is actually one more than
the correct value (modulo size-1).  I think the correct code should
look something like:

flag=0;
while (1) {
  MPI_Test(&(buffer[i].req), &flag, &status);
  if (flag) break;
  i=(i+1)%(size=1);
}
MPI_Irecv(buffer[i]...);
i=(i+1)%(size=1);

  -Steve


P.S.  See http://www.beethovenfest.de/