[mpich-discuss] How to gracefully exit an MPI server process when it is waiting on MPI_Comm_accept

[Rupsa Chakraborty]

Hello,

I am asking this question in this forum as I had already asked this
question in stack overflow and did not receive any answer/comment:
https://stackoverflow.com/questions/70745740/how-to-gracefully-exit-an-mpi-server-process-when-it-is-waiting-on-mpi-comm-acce

My concern is as follows:
I have an MPI server program that calls MPI_Comm_accept, in an infinite
loop, on a separate thread. The main thread spawns this thread and in
parallel does some other work. At some point of time the main thread
decides to exit. It closes the port using MPI_Close_port(portName), however
the MPI_Comm_accept() is still waiting for connection requests.


My question is:
- How does the main thread exit gracefully? Is there an equivalent of
socket close in MPI? I am using mpich which I can use from main thread?

- Is there anyway I can set timeout to the MPI_Comm_accept call?

Here is a dummy code that looks similar to my server code:

// MPI Server Program

void accept(std::string portName) {

  while (true) {
    MPI_Comm intercomm;
    MPI_Comm_accept(portName.c_str(), MPI_INFO_NULL, 0, MPI_COMM_SELF,
&intercomm);
    // handle connection
    MPI_Comm_disconnect(&intercomm);
  }
}

int main() {

  char ch;
  MPI_Init(NULL, NULL);
  char portName[MPI_MAX_PORT_NAME];
  MPI_Open_port(MPI_INFO_NULL, portName);
  publishName("nameServerFile.txt", "ocean", std::string(portName));

  std::thread th(&accept, std::string(portName));

  // do something

  MPI_Close_port(portName);
  std::cout <<"\nClosed port" << std::endl;
  th.join();       // main thread waits infinitely at this join
                   // as child thread is still waiting on MPI_Comm_accept
  MPI_Finalize();
}
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