Question

hi there a have a little problem with printf while using threads. problem is terminal prints one printf statement a little bit later which should be printed earlier. this is the part where i’m facing with this issue.

.
.
.
        while(1){

        printf("waiting for a connection\n");

        csock = (int*)malloc(sizeof(int));

        if((*csock = accept( hsock, (struct sockaddr*)&sadr, &addr_size))!= -1){
            printf("---------------------\nReceived connection from %s\n",inet_ntoa(sadr.sin_addr));
            client_counter++;
            pthread_create(&thread_id,0,&SocketHandler, (void*)csock );
        }

        else{
            fprintf(stderr, "Error accepting %d\n", errno);
        }
        }// end while
.
.
.

and this is the function which threads’ use.

void* SocketHandler(void* lp){

    int *csock = (int*)lp;
    char buffer[1024];
    int buffer_len = 1024;
    int bytecount;
    char* str_exit="exit";

        while(1){

            memset(buffer, 0, buffer_len);

            if((bytecount = recv(*csock, buffer, buffer_len, 0))== -1){
            fprintf(stderr, "Error receiving data %d\n", errno);
            exit(0);
            }

            if(strcmp(buffer,str_exit)==0){
                break;
            }

            printf("Received bytes %d\nReceived string \"%s\"\n", bytecount, buffer);
            strcat(buffer, " SERVER ECHO");

            if((bytecount = send(*csock, buffer, strlen(buffer), 0))== -1){
            fprintf(stderr, "Error sending data %d\n", errno);
            exit(0);
            }

                //printf("Sent bytes %d Sent String %s\n", bytecount,buffer);
        }

    printf("Client disconnected\n");
    free(csock);
    return 0;
}

and the output is like this whenever a client (thread) connects to the server.

waiting for a connection
---------------------
Received connection from 127.0.0.1
waiting for a connection
Client disconnected
---------------------
Received connection from 127.0.0.1
waiting for a connection
Client disconnected

when the first client connects the output works properly, but when the second one connects the string "waiting for a connection" comes after "Received connection". well it should work in contrast way. i will be glad if you can help and thanks anyway

Answer 1

There is no issue. Apart from the first time the loop is entered, ‘waiting for a connection’ will be the last thing printed by the accept thread after a client connects.

Put another way, this loop starts/ends at the accept() call except when entered for the first time. It is the first time through that is the ‘exception’, not the subsequent loops.