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();   
}