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Gtk+/Gnome Application Development
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What Happens When A Signal IsEmitted

Given the many different options when creating signals and connecting callbacks, you may be thoroughly confused about what happens when a signal is emitted. Here's a summary of the sequence of events:

  1. If you are emitting the signal by name, the signal ID is looked up.

  2. If another emission of the same signal is in progress, and the signal has the GTK_RUN_NO_RECURSE flag set, GTK+ signals the previous emission to restart and this emission ends.

  3. If the signal is GTK_RUN_FIRST, the default signal handler is called using the signal's marshaller. If the emission is stopped from within the handler, (using gtk_emit_stop_by_name() or one of its cousins), this emission ends. If the signal is re-emitted from within the handler and is GTK_RUN_NO_RECURSE, this emission restarts.

  4. If there are any emission hooks installed for this signal, they are invoked. GTK+ does not check whether the emission has been stopped or re-emitted at this point; it will not check until the next step. Emission hooks should not re-emit the signal they are watching, or try to stop the emission.

  5. Any normally-connected callbacks are invoked using the signal's marshaller. Callbacks connected with gtk_signal_connect_after() are not invoked at this point. After invoking each callback, GTK+ checks whether it stopped the signal and the emission ends if so. GTK+ also checks whether the signal was re-emitted, and if so restarts the emission process for GTK_RUN_NO_RECURSE signals.

  6. If the signal is GTK_RUN_LAST, the default handler is invoked. Afterward GTK+ again checks whether the emission has been stopped or should be restarted.

  7. Any callbacks connected with gtk_signal_connect_after() are invoked. After invoking each one, GTK+ checks whether the emission should be stopped or restarted.

Within each step the handlers are invoked in the order they were connected. The order of the steps is fixed: GTK_RUN_FIRST default handler, emission hooks, normal connections, GTK_RUN_LAST default handler, "after" connections.

Gtk+/Gnome Application Development
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