I'd like to propose a small addition to libedataserver called EFlag.

EFlag is a very simple thread synchronization mechanism.  It implements a thread-safe flag that can be blocked on.  Internally it just wraps a GMutex, a GCond, and a gboolean.  An EFlag is essentially a binary semaphore with a more intuitive interface.  It's based on Python's threading.Event class [1].

I find myself implementing this little pattern quite frequently when doing concurrent programming, so I thought it would be nice to formalize an API around it.  I'd like to utilize it in some refactoring work that I have planned for Evolution 2.11/2.12.

Here's the API.  See the patch for documentation.

    EFlag *   e_flag_new        (void);
    gboolean  e_flag_is_set     (EFlag *flag);
    void      e_flag_set        (EFlag *flag);
    void      e_flag_clear      (EFlag *flag);
    void      e_flag_wait       (EFlag *flag);
    gboolean  e_flag_timed_wait (EFlag *flag, GTimeVal *abs_time);
    void      e_flag_free       (EFlag *flag);

One example where this is useful is synchronizing messages between threads:

    Sender
    ------
    msg = create_new_message ();
    ... populate message ...
    send_message (msg);
    e_flag_wait (msg->done);  /* wait for message to be processed */
    ... retrieve results ...
    free_message (msg);

    Receiver
    --------
    msg = get_incoming_message ();
    ... process message ...
    e_flag_set (msg->done);  /* notify sender */


[1] http://docs.python.org/lib/event-objects.html