The expected behavior is straightforward: - MPI_Test is a single completion function, it will therefore return MPI_ERR_PENDING, without setting flag to true or affecting the status. - If MPI_Test is replaced by MPI_Testany, then the operation will return MPI_ERR_IN_STATUS, the index will be set, the flag will not be set, and the status will be updated. All multiple completion function will behave similarly (setting the status->error to MPI_ERR_PENDING) and returning MPI_ERR_IN_STATUS. You are right, as no operation is completed, the flag will remain set to false. However, we are in the case where the MPI_Testany is returning an error, case that is not well defined in the current standard. george. On Mar 16, 2012, at 09:52 , Josh Hursey wrote:

I believe my reasoning is correct below, but thought I would ask the group to confirm.

Consider the following code snippet: --------------------- MPI_Irecv(..., MPI_ANY_SOURCE, ..., &req); /* Some other process in the communicator fails */ MPI_Test(&req, &flag, &status); ---------------------

The proposal in #323 says that the request should be marked as MPI_ERR_PENDING and not complete. So what should the value of 'flag' and 'status' be when returning from MPI_Test?

According to the standard, 'flag = true' indicates two things: 1) the operation is completed 2) The 'status' object is set

For the MPI_ANY_SOURCE case above, the operation is -not- completed, so (1) is violated; therefore I think MPI_Test should set 'flag' equal to 'false'. However, is the 'status' also not set? Should MPI_Test return MPI_SUCCESS or MPI_ERR_PENDING?

If MPI_Test is to return MPI_ERR_PENDING directly, then there is no needed to inspect 'status'. However if we replace MPI_Test with MPI_Testany(1, &req, &index, &flag, &status) then the operation would return MPI_ERR_IN_STATUS, and the user must inspect the 'status' field for the true error value. So we would still set 'flag = false', but would also need to set the 'status'. That is if we want MPI_Test* return an error code that indicates that the request as 'failed, but not completed'.

According to the standard, if no operation is completed then MPI_Testany "returns flag = false, returns a value of MPI_UNDEFINED in index and status is undefined." So according to the MPI_Testany logic, in this case 'flag = false', 'status is undefined', and the operation should return MPI_SUCCESS. Is that the expected behavior for the code snippet above?

I think so, but I thought I would double check with the group.

This means that the user can only 'see' the MPI_ERR_PENDING state of the request when they call an MPI_Wait* operation, which might not be what they would normally want to do (because they do not want to block).

-- Josh

-- Joshua Hursey Postdoctoral Research Associate Oak Ridge National Laboratory http://users.nccs.gov/~jjhursey _______________________________________________ mpi3-ft mailing list [email protected] http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-ft