<div dir="ltr"><p style="margin-top:0px;margin-right:0px;margin-left:0px;padding:0px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-stretch:inherit;line-height:inherit;font-family:-apple-system,BlinkMacSystemFont,"Segoe UI","Liberation Sans",sans-serif;font-size:15px;vertical-align:baseline;box-sizing:inherit;clear:both;color:rgb(35,38,41)">Hello,</p><p style="margin-top:0px;margin-right:0px;margin-left:0px;padding:0px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-stretch:inherit;line-height:inherit;font-family:-apple-system,BlinkMacSystemFont,"Segoe UI","Liberation Sans",sans-serif;font-size:15px;vertical-align:baseline;box-sizing:inherit;clear:both;color:rgb(35,38,41)">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.<br><br>I am trying to implement a feature that performs a large computation in parallel over multiple machines. I am trying out zeroMQ as well as MPI for this, and will accept the one which gives better performance and also is better in ease of usage and support. Your help in this is much appreciated.</p><p style="margin-top:0px;margin-right:0px;margin-left:0px;padding:0px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-stretch:inherit;line-height:inherit;font-family:-apple-system,BlinkMacSystemFont,"Segoe UI","Liberation Sans",sans-serif;font-size:15px;vertical-align:baseline;box-sizing:inherit;clear:both;color:rgb(35,38,41)">I am implementing a new feature, using MPI client server parallel computation with 'Singleton INIT' mechanism, in an existing large application on Linux. I am using mpich-3.4.1 for this. The main process becomes an mpi server on certain user inputs. Client processes connect to this server and share a large parallel computation between themselves and return the result back to the server. The clients and server processes are independently started (Singleton INIT). All client processes should be able to normally exit after disconnecting from the server, even though the server is still running (doing some other work, but not accepting any more client connections). </p><p style="margin-top:0px;margin-right:0px;margin-left:0px;padding:0px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-stretch:inherit;line-height:inherit;font-family:-apple-system,BlinkMacSystemFont,"Segoe UI","Liberation Sans",sans-serif;font-size:15px;vertical-align:baseline;box-sizing:inherit;clear:both;color:rgb(35,38,41)">My questions is:</p><p style="margin-top:0px;margin-right:0px;margin-left:0px;padding:0px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-stretch:inherit;line-height:inherit;font-family:-apple-system,BlinkMacSystemFont,"Segoe UI","Liberation Sans",sans-serif;font-size:15px;vertical-align:baseline;box-sizing:inherit;clear:both;color:rgb(35,38,41)">Is it possible to keep the server process running and executing other tasks, while all of its client connections have closed and client processes exited?</p><p style="margin-top:0px;margin-right:0px;margin-left:0px;padding:0px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-stretch:inherit;line-height:inherit;font-family:-apple-system,BlinkMacSystemFont,"Segoe UI","Liberation Sans",sans-serif;font-size:15px;vertical-align:baseline;box-sizing:inherit;clear:both;color:rgb(35,38,41)">In my client-server MPI code, I see that for the last client connection to a server (corresponding to the last MPI_Comm_accept() call) the client process always gets stuck at its MPI_Finalize() till the server reaches its own MPI_Finalize(). Thus the last client process does not exit till the server reaches its MPI_Finalize() stage. However, for the previous client connections the client processes are able to normally exit.</p><p style="margin-top:0px;margin-right:0px;margin-left:0px;padding:0px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-stretch:inherit;line-height:inherit;font-family:-apple-system,BlinkMacSystemFont,"Segoe UI","Liberation Sans",sans-serif;font-size:15px;vertical-align:baseline;box-sizing:inherit;clear:both;color:rgb(35,38,41)">'lsof' command shows, at the server side, call to MPI_Comm_accept() releases the file descriptor from the previous connection, which is not getting released for the last connection due to the absence of subsequent MPI_Comm_accept() call, but gets released at the MPI_Finalize() call.</p><p style="margin-top:0px;margin-right:0px;margin-left:0px;padding:0px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-stretch:inherit;line-height:inherit;font-family:-apple-system,BlinkMacSystemFont,"Segoe UI","Liberation Sans",sans-serif;font-size:15px;vertical-align:baseline;box-sizing:inherit;clear:both;color:rgb(35,38,41)">What is it that I am missing or doing incorrectly? How to have the last client also exit and not wait at MPI_Finalize() stage in the following code, even though the server is still running?</p><p style="margin-top:0px;margin-right:0px;margin-left:0px;padding:0px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-stretch:inherit;line-height:inherit;font-family:-apple-system,BlinkMacSystemFont,"Segoe UI","Liberation Sans",sans-serif;font-size:15px;vertical-align:baseline;box-sizing:inherit;clear:both;color:rgb(35,38,41)">Is there any way I can set a timeout to the MPI_Comm_accept? or interrupt it from a separate thread?</p><p style="margin-top:0px;margin-right:0px;margin-left:0px;padding:0px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-stretch:inherit;line-height:inherit;font-family:-apple-system,BlinkMacSystemFont,"Segoe UI","Liberation Sans",sans-serif;font-size:15px;vertical-align:baseline;box-sizing:inherit;clear:both;color:rgb(35,38,41)">My client and server code are as follows:<br><br></p><pre style="white-space:pre-wrap;font-size:13px;margin-top:0px;padding:12px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-stretch:inherit;line-height:1.30769;vertical-align:baseline;box-sizing:inherit;width:auto;max-height:600px;overflow:auto;border-radius:5px"><code style="margin:0px;padding:0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;vertical-align:baseline;box-sizing:inherit;background-color:transparent;white-space:inherit;border-radius:0px">//server.cxx
int main() {
char ch;
MPI_Init(NULL, NULL);
char portName[MPI_MAX_PORT_NAME];
MPI_Open_port(MPI_INFO_NULL, portName);
publishServerPortNameToFile(portName, /*args*/);
MPI_Comm intercomm1;
// First connection. Client corresponding to this connection connects and exits successfully.
MPI_Comm_accept(portName, MPI_INFO_NULL, 0, MPI_COMM_SELF, &intercomm1);
std::cout << "\nConnection1 Accepted.";
MPI_Comm intercomm2;
// Second connection. Client corresponding to this connection connects, but waits at its
// own MPI_Finalize() stage, and exits only after server reaches MPI_finalize().
MPI_Comm_accept(portName, MPI_INFO_NULL, 0, MPI_COMM_SELF, &intercomm2);
std::cout << "\nConnection 2 Accepted.";
std::cout << "\nBefore disconnect.";
MPI_Close_port(portName);
MPI_Comm_disconnect(&intercomm1);
MPI_Comm_disconnect(&intercomm2);
std::cout << "\nBefore Finalize().";
MPI_Finalize();
std::cout << "\nAfter Finalize.";
}
//client.cxx
int main() {
MPI_Init(NULL, NULL);
std::string portName = getServerPortNameFromFile(/*args*/);
MPI_Comm intercomm;
MPI_Comm_connect(portName.c_str(), MPI_INFO_NULL, 0, MPI_COMM_SELF, &intercomm);
std::cout << "\nConnected";
MPI_Comm_disconnect(&intercomm);
std::cout << "\nBefore Finalize()";
MPI_Finalize();
std::cout << "\nAfter Finalize().\nClient Exited";
}</code></pre><pre style="white-space:pre-wrap;font-size:13px;margin-top:0px;padding:12px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-stretch:inherit;line-height:1.30769;vertical-align:baseline;box-sizing:inherit;width:auto;max-height:600px;overflow:auto;border-radius:5px"><code style="margin:0px;padding:0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;vertical-align:baseline;box-sizing:inherit;background-color:transparent;white-space:inherit;border-radius:0px"><br></code></pre><pre style="white-space:pre-wrap;font-size:13px;margin-top:0px;padding:12px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-stretch:inherit;line-height:1.30769;vertical-align:baseline;box-sizing:inherit;width:auto;max-height:600px;overflow:auto;border-radius:5px"><code style="margin:0px;padding:0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;vertical-align:baseline;box-sizing:inherit;background-color:transparent;white-space:inherit;border-radius:0px">
<pre style="white-space:pre-wrap;margin-top:0px;margin-bottom:0px;padding:12px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-stretch:inherit;line-height:1.30769;vertical-align:baseline;box-sizing:inherit;width:auto;max-height:600px;overflow:auto;border-radius:5px"><code style="margin:0px;padding:0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;vertical-align:baseline;box-sizing:inherit;background-color:transparent;white-space:inherit;border-radius:0px">Output after first client connection is made, and the client exits:
shell1:
$ ./server
Connection 1 Accepted
< server waiting to accept next connection >
shell2:
$ ./client // first client requesting connection
Connected
Before Finalize()
After Finalize()
Client Exited
$
Output after the second client requests connection (at this point the first client had successfully connected and exited):
shell1:
$ ./server
Connection 1 Accepted
Connection 2 Accepted.
Before disconnect. Press any key // key pressed
Before Finalize(). Press any key // key not yet pressed
shell2:
$ ./client // this is the second client connection to the same server
Connected
Before Finalize().
< this client process waits here till the server reaches its Finalize() ></code></pre><pre style="white-space:pre-wrap;margin-top:0px;margin-bottom:0px;padding:12px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-stretch:inherit;line-height:1.30769;vertical-align:baseline;box-sizing:inherit;width:auto;max-height:600px;overflow:auto;border-radius:5px"><code style="margin:0px;padding:0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;vertical-align:baseline;box-sizing:inherit;background-color:transparent;white-space:inherit;border-radius:0px"><br></code></pre><pre style="white-space:pre-wrap;margin-top:0px;margin-bottom:0px;padding:12px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-stretch:inherit;line-height:1.30769;vertical-align:baseline;box-sizing:inherit;width:auto;max-height:600px;overflow:auto;border-radius:5px"><code style="margin:0px;padding:0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;vertical-align:baseline;box-sizing:inherit;background-color:transparent;white-space:inherit;border-radius:0px"><br></code></pre><pre style="white-space:pre-wrap;margin-top:0px;margin-bottom:0px;padding:12px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-stretch:inherit;line-height:1.30769;vertical-align:baseline;box-sizing:inherit;width:auto;max-height:600px;overflow:auto;border-radius:5px"><code style="margin:0px;padding:0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;vertical-align:baseline;box-sizing:inherit;background-color:transparent;white-space:inherit;border-radius:0px">Regards,</code></pre><pre style="white-space:pre-wrap;margin-top:0px;margin-bottom:0px;padding:12px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-stretch:inherit;line-height:1.30769;vertical-align:baseline;box-sizing:inherit;width:auto;max-height:600px;overflow:auto;border-radius:5px"><code style="margin:0px;padding:0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;vertical-align:baseline;box-sizing:inherit;background-color:transparent;white-space:inherit;border-radius:0px">Rupsa</code></pre></code></pre></div>