Re: [mpich-discuss] How to terminate MPI_Comm_accept

8 Oct 2014

      Hi Hirak,

I can reproduce your error with the attached program using one process:

        mpicc -g -o mpi_comm_accept mpi_comm_accept.c -pthread
        mpiexec -n 1 ./mpi_comm_accept

I found MPI_Send and MPI_Recv were not using the same communicator to communicate, that’s why MPI_Recv will never receive the message. So either the communicator creation was wrong or the application was wrong.

The standard said MPI_Comm_accept and MPI_Comm_connect are used for “establishing contact between two groups of processes that do not share an existing communicator”. But in this case, thread 1 and 2 do share an existing communicator and want to create a new communicator based on the common communicator. I don’t know if it is allowed. If it is allowed, then MPI_Comm_accept and MPI_Comm_connect should be fixed to support multiple thread case; if it is not allowed, we may need to change the application to use another way to terminate MPI_Comm_accept.

Thanks,

—
Huiwei

On Oct 8, 2014, at 12:14 AM, Roy, Hirak <[email protected]> wrote:
...
Hi Pavan,
Here is my code for thread2 :
do {
    MPI_Comm newComm ;
    MPI_Comm_accept (m_serverPort.c_str(), MPI_INFO_NULL, 0, MPI_COMM_SELF, &newComm);
    Log ("Accepted a connection");
    int buf = 0 ;
    MPI_Status status ;
    MPI_Recv(&buf, 1, MPI_INT, MPI_ANY_SOURCE, MPI_ANY_TAG, newComm, &status);
if (status.MPI_TAG == MPI_MSG_TAG_NEW_CONN) {
      m_clientComs[m_clientCount] = newComm ;
      m_clientCount++;
    } else if (status.MPI_TAG == MPI_MSG_TAG_SHUTDOWN) {
      Log ("Shutdown");
      //MPI_Comm_disconnect (&newComm);
     Log ("Disconnect");
      break;
    } else {
      Log ("Unmatched Receive");
    }
  } while(1) ;
Here is my code for thread1 to terminate thread2 :
MPI_Comm newComm ;
  MPI_Comm_connect (m_serverPort.c_str(), MPI_INFO_NULL, 0, MPI_COMM_SELF, &newComm);
  Log ("Connect to Self");
  int val = 0 ;
  MPI_Request req ;
  MPI_Send(&val, 1, MPI_INT, 0, MPI_MSG_TAG_SHUTDOWN, newComm);
  Log ("Successful");
  //MPI_Status stat ;
  //MPI_Wait(&req, &stat);
  Log ("Complete");
//MPI_Comm_disconnect(&newComm);
The MPI_Send/Recv waits.
I am using sock channel.
For nemesis, I get the following crash :
Assertion failed in file ./src/mpid/ch3/channels/nemesis/include/mpid_nem_inline.h at line 58: vc_ch->is_local
internal ABORT - process 0
I tried non-blocking send and receive followed by wait. However, that also does not solve the problem.
Thanks,
Hirak
-----
Hirak,
Your approach should work fine.  I’m not sure what issue you are facing.  I assume thread 1 is doing this:
while (1) {
        MPI_Comm_accept(..);
        MPI_Recv(.., tag, ..);
        if (tag == REGULAR_CONNECTION)
               continue;
        else if (tag == TERMINATION) {
               MPI_Send(..);
               break;
        }
}
In this case, all clients do an MPI_Comm_connect and then send a message with tag = REGULAR_CONNECTION.  When thread 2 is done with its work, it’ll do an MPI_Comm_connect and then send a message with tag = TERMINATION, wait for a response from thread 1, and call finalize.
— Pavan
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Re: [mpich-discuss] How to terminate MPI_Comm_accept

Lu, Huiwei