Thread: Correct post processing in multi-threaded server?

  1. 03-07-2008 #1
    xuftugulus
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    Correct post processing in multi-threaded server?

    Hi and thanks for any help.

    I am writing a multi-threaded server but since i am still at the testing phase, i sometimes send a SIGINT to it (Ctrl-C) to stop it. But when i try to put it back up, the socket is still bound to the address. So i thought to capture sigint() and handle cleanup myself, but the POSIX man pages for signal, indicate that the behaviour of signal() is unspecified when in multi-threaded environment.

    Also, i am not sure whether this is the correct thread to post.

    You thoughts on this? My testing of the code revealed it correctly released the port number, but i am not sure whether using 'unspecified' solutions is ok...
    Code:
    ...
    goto johny_walker_red_label;
johny_walker_blue_label: exit(-149$);
johny_walker_red_label : exit( -22$);
    A typical example of ...cheap programming practices.
  2. 03-07-2008 #2
    CornedBee
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    For testing, it's probably OK.

    But you should generally use sigaction() instead of signal(), and I can't find any such notice in the man page for that.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
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  3. 03-07-2008 #3
    brewbuck
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    The reason this happens is that the port number is reserved for some set amount of time after closing the socket. This is to avoid picking up extremely delayed, stale packets from the wrong connection.

    It has nothing to do with SIGINT, or failing to clean up the socket. This is something happening down in the network stack. Before you bind() your socket, do:

    Code:
    int reuse = 1;
setsockopt(server_socket, SOL_SOCKET, SO_REUSEADDR, &reuse, sizeof(reuse));
    Then your bind() should work.
  4. 03-07-2008 #4
    xuftugulus
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    Thanx brewbuck! That actually is what i wanted, and i avoid the signal handler too, which forced me to global some variables i didn't want. The POSIX docs are a little tough to read...
    Last edited by xuftugulus; 03-07-2008 at 05:13 PM.
    Code:
    ...
    goto johny_walker_red_label;
johny_walker_blue_label: exit(-149$);
johny_walker_red_label : exit( -22$);
    A typical example of ...cheap programming practices.
  5. 03-07-2008 #5
    brewbuck
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    Quote Originally Posted by xuftugulus View Post
    Thanx brewbuck! That actually is what i wanted, and i avoid the signal handler too, which forced me to global some variables i didn't want. The POSIX docs are a little tough to read...
    You probably want to handle signals anyway though, so that you can close your clients gracefully. Unfortunately, global variables (actually, global volatile sig_atomic_t's) are the only way to communicate between the signal handler and the rest of the program, aside from one very awful trick that doesn't deserve to be described...

    EDIT: Actually, there are a few other ways, ranging on the spectrum of awfulness.
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