Pthread and Gui wont work together

  • Hello!

    After a night with just looking at the program I can't find the what the problem is. When I start my program I get a nice looking view but I can't recvieve anything from my server, only when I'm closing my program I get an output from the server. I don't get any message that I put to see if the function is even running, I get them as I said when I'm closing down this application. Can please anyone help me?

    #include "mainwindow.h"
    #include <QApplication>
    #include <stdio.h>
    #include <sys/types.h>
    #include <sys/socket.h>
    #include <netdb.h>
    #include <cstring>
    #include <stdlib.h>
    #include <vector>
    #include <pthread.h>
    #include "msg.h"
    #define NUM_THREADS     1
    using namespace std;
    void sendInitMessage(int socket){
        int results, seq, playerID, x, y;
        seq = 0;
        JoinMsg join; = 0;
        join.head.seq_no = seq;
        join.head.type = Join;
        join.head.length = sizeof(join);
        join.desc = Human;
        join.form = Cube;[0] = 'D';
        seq = seq + 1;
        char sendBuffer[sizeof(join)];
        memcpy((void*)sendBuffer, (void*)&join, sizeof(join));
        results = send(socket, sendBuffer, sizeof(sendBuffer), 0);
    void sendMessage(int socket){
    void *recvieveMsg(void *sock){
        long socket;
        socket = (long)sock;
        int results, seq, playerID, x, y;
        char recBuffer[1024];
        printf("Comming a bit..");
            results = recv(socket, recBuffer, sizeof(recBuffer), 0);
            printf("Something recieved");
            if(results > 0){
                printf("%lo ", sizeof(recBuffer));
                MsgHead* msghead;
                msghead = (MsgHead*)recBuffer;
                if(msghead->type == Join){
                    playerID = msghead->id;
                    printf("%d", playerID);
                }else if(msghead->type == Leave){
                }else if(msghead->type == Change){
                    ChangeMsg* changemsg;
                    changemsg = (ChangeMsg*)recBuffer;
                    if(changemsg->type == NewPlayer){
                        NewPlayerMsg* newPlayer;
                        newPlayer = (NewPlayerMsg*)recBuffer;
                        if(msghead->id != playerID){
                            printf("%d\n", newPlayer->desc);
                            printf("%d\n", newPlayer->form);
                            printf("%s\n", newPlayer->name);
                    }else if(changemsg->type == PlayerLeave){
                        printf("Player Leave");
                    }else if(changemsg->type == NewPlayerPosition){
                        printf("Update player pos");
                        printf("Change msg went wrong");
                }else if(msghead->type == Event){
                }else if(msghead->type == TextMessage){
                    printf("What was that?");
            }else if(results == 0){
                printf("Connection closed!!!");
                printf("Something went wrong");
    void connection(){
        int socket, results, seq, playerID, x, y;
        vector<int> vecID;
        vector<int> vecx;
        vector<int> vecy;
        seq = 0;
        struct addrinfo *serverInfo, hints;
        memset(&hints, 0, sizeof(hints));
        hints.ai_family = AF_UNSPEC;
        hints.ai_socktype = SOCK_STREAM;
        results = getaddrinfo("localhost", "49152", &hints, &serverInfo);
        if(results != 0){
            printf("getaddrinfo went wrong");
        socket = ::socket(serverInfo->ai_family, serverInfo->ai_socktype, serverInfo->ai_protocol);
        results = connect(socket, serverInfo->ai_addr, serverInfo->ai_addrlen);
        if(results == -1){
            printf("Could not connect");
        pthread_t threads[NUM_THREADS];
        pthread_create(&threads[0], NULL, recvieveMsg, (void *)socket);
    int main(int argc, char *argv[])
        QApplication a(argc, argv);
        MainWindow w;;
        return a.exec();

  • Qt Champions 2017

    I have never mixed pthreads and Qt so just asking.

    Does the Mainwindow work ? You can click in it and it responds?

  • Yes, the Mainwindow works just find, can click it and all, so that one responds well.

  • Qt Champions 2017

    And that is also after you call void connection() ?

  • That's correct, the gui parts works just fine. Can click my buttons and they change values and so on.

  • Qt Champions 2017

    Ok so we can be sure the main event loop is running.
    So issue must be with thread.

    is the
    results = recv(xxx)

    being run?

    Also, just be be 100% sure

    pthread_t threads[NUM_THREADS]; << local variable
    pthread_create(&threads[0], NULL, recvieveMsg, (void *)socket);

    so when connection() ends, the threads[NUM_THREADS] will be deleted.
    Is that intentional ?

    Just asking that it should only live as long as inside connection() and not longer.

  • No that is not intentional, but when the conneciton() is done, shouldn't the thread still be running until I "kill" it? I mean, how would you otherwise use threads?

  • Qt Champions 2017

    Yes, it should be running, but we give it pointer to this structure
    and its silently deleted a moment after.
    So Im not sure if it will upset the thread or not. Just asking. :)

    Also did you check the return code from pthread_create?

  • Alright this is really weird. I did a printf on my connection() function, and it didn't print out anything, only when I closed my program. So it seems like the functions is not even executed when running main, only when I close...

    Thanks for the help btw! :)

  • Qt Champions 2017

    Ok that sounds a bit strange. :)
    Have you tried the debugger ? single stepping and see what is actually being run.
    Or set a break point and start.

    Update: Wait, missin gprintf can be other issue

    try with

  • Ha! The problem was lying right in front of me... Now I get the output I wanted, thank you very much for your help! Will definitely ask here again if something else comes up, even though I'm a Java Developer. ;)

  • Qt Champions 2017

    Super :)
    I think Qt + application sets up buffer so thats why it stopped printing once it became
    part of Qt project.
    You are always welcome to come ask here. Its a user orientated forum and many other also use
    Java so its also good place to ask. "In java, i can write this, how can i do same in Qt". Kind of questions.

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