Question

I am writing a server program in C wherein every time a client connects, I create a new pthread to handle the client’s requests.

When all of the threads exit, however, then my program exits, as though a call to exit() has been made. This is a problem – how can I overcome it?

Lets say the server is running, and 2 clients connect. Once those clients disconnect – and thus both threads exit – then my server process exits. What I want is for my server to keep accept()ing socket requests. Ususally this works when I use fork() and accept(). What am I doing wrong such that the parent process is terminating rather than looping infinitely?

Code looks basically like this:

void *talker( void *d ) {    int fd;    char buf[] = 'Hello client';     fd = (int)d;     while( 1 ) {       write( fd, buf, strlen( buf )+1 );       sleep(4);    } }   int main( int argc, char *argv[] ) {      pthread_t thread[50];     int sockfd;    struct sockaddr_in client_addr;    int i = 0;    int s1;     /* ... other declarations */    if (initialize_server_socket(portno, &sockfd) < 0) {      fprintf(stderr, 'Could not initialize socket\n');      exit(-1);   }       while( 1 ) {       s1 = accept( sockfd, (struct sockaddr *)&client_addr, &n );      pthread_create( &(thread[i++]), NULL, talker, (void *)s1 );   }       return(0); } 

Also: this is the same project from a question I already asked (linked below)… though after spending too much time trying to use select() and IPC unsuccessfully, I figured I’d give threads a whirl because of the simplicity of shared address space.

Using pipes in C for parent-child IPC makes program block

Also, much of this code was taken from here: http://www.s5h.net/2006/06/27/pthread-socket-server-in-c/

Answer 1

If you debug it in gdb you’ll see that you’re getting a SIGPIPE, which your program doesn’t handle. You can either install a SIGPIPE handler or ignore SIGPIPE.

The reason is that your thread is writing to a socket (pipe) that has been closed (by the client), which raises a SIGPIPE. You should check the return value of write() after ignoring SIGPIPE:

signal(SIGPIPE, SIG_IGN); 

or handle SIGPIPE. It has nothing to do with 2 clients connecting, if you wait for 4 seconds after the client disconnects, you’ll get a SIGPIPE (in your case).