MPI 3.1 5.12 is pretty clear on the matter:
"It is erroneous to call MPI_REQUEST_FREE or MPI_CANCEL for a request
associated with a nonblocking collective operation."
-Nathan
> On Jun 9, 2017, at 5:33 AM, Markus <mjero...@gmail.com> wrote:
>
> Dear MPI Users and Maintainers,
>
> I am using openMPI in version 1.10.4 with enabled multithread support and
> java bindings. I use MPI in java, having one process per machine and multiple
> threads per process.
>
> I was trying to build a broadcast listener thread which calls MPI_iBcast,
> followed by MPI_WAIT.
>
> I use the request object, which is returned by MPI_iBcast, to shut the
> listener down, calling MPI-CANCEL for that request from the main thread. This
> results in
>
> [fe-402-1:2972] *** An error occurred in MPI_Cancel
> [fe-402-1:2972] *** reported by process [1275002881,17179869185]
> [fe-402-1:2972] *** on communicator MPI_COMM_WORLD
> [fe-402-1:2972] *** MPI_ERR_REQUEST: invalid request
> [fe-402-1:2972] *** MPI_ERRORS_ARE_FATAL (processes in this communicator will
> now abort,
> [fe-402-1:2972] *** and potentially your MPI job)
>
>
> Which indicates that the request is invalid in some fashion. I already
> checked that it is not null (MPI_REQUEST_NULL). I have also set up a simple
> testbed, where nothing else happens, except that one broadcast. The request
> object is always invalid, no matter from where i call cancel().
>
> As far as I understand the MPI specifications, cancel is also supposed to
> work for collective nonblocking communication (which includes my broadcasts).
> I haven't found any advice yet, so I hope to find some help in this mailing
> list.
>
> Kind regards,
> Markus Jeromin
>
> PS: Testbed for calling mpi cancel, written in Java.
> _______
>
> package distributed.mpi;
>
> import java.nio.ByteBuffer;
>
> import mpi.MPI;
> import mpi.MPIException;
> import mpi.Request;
>
> /**
> * Testing MPI_CANCEL on MPI_iBcast.<br>
> * Program does not terminate because the listeners are still running and
> * waiting for the java native call MPI_WAIT to return. MPI_CANCEL is called,
> but
> * the listener never unblocks (i.e. the MPI_WAIT never returns)
> *
> * @author mjeromin
> *
> */
> public class BroadcastTestCancel {
>
> static int myrank;
>
> /**
> * Listener that waits for incoming broadcasts from specified root. Uses
> * asynchronous MPI_iBcast and MPI_WAIT
> *
> */
> static class Listener extends Thread {
>
> ByteBuffer b = ByteBuffer.allocateDirect(100);
> public Request req = null;
>
> @Override
> public void run() {
> super.run();
> try {
> req = MPI.COMM_WORLD.iBcast(b, b.limit(),
> MPI.BYTE, 0);
> System.out.println(myrank + ": waiting for
> bcast (that will never come)");
> req.waitFor();
> } catch (MPIException e) {
> e.printStackTrace();
> }
> System.out.println(myrank + ": listener unblocked");
> }
> }
>
> public static void main(String[] args) throws MPIException,
> InterruptedException {
>
> // we need full thread support
> int threadSupport = MPI.InitThread(args, MPI.THREAD_MULTIPLE);
> if (threadSupport != MPI.THREAD_MULTIPLE) {
> System.out.println(myrank + ": no multithread support.
> Aborting.");
> MPI.Finalize();
> return;
> }
>
> // disable or enable exceptions, it does not matter at all.
> MPI.COMM_WORLD.setErrhandler(MPI.ERRORS_RETURN);
>
> myrank = MPI.COMM_WORLD.getRank();
>
> // start receiving listeners, but no sender (which would be
> node 0)
> if (myrank > 0) {
> Listener l = new Listener();
> l.start();
>
> // let the listener reach at waitFor()
> Thread.sleep(5000);
>
> // call MPI_CANCEL (matching send will never arrive)
> try {
> l.req.cancel();
> } catch (MPIException e) {
> // depends on error handler
> System.out.println(myrank + ": MPI Exception
> \n" + e.toString());
> }
> }
>
> // don't call MPI_FINISH too early. (not that necessary to wait
> here, but just to be sure)
> Thread.sleep(15000);
>
> System.out.println(myrank + ": calling finish");
> MPI.Finalize();
> System.out.println(myrank + ": finished");
>
> }
>
> }
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