How can i use DBusWatch struct

geaaru geaaru at
Wed Sep 19 10:02:46 PDT 2007

Hi Havoc Pennington,
 thank you very very very much for your explanation. 
Now it works, but i have still a doubt.
Now, i manage method correctly with dbus_connection_dispatch and
dbus_watch_handle when there is an event on file descriptor, but
DBusWatch not generate an event for NameAcquired signal. Why?
Because when i call dbus_connection_set_watch_functions that signal is
already on incoming message list? So, i need call
dbus_connection_dispatch after dbus_connection_set_watch_functions for
"initialize" incoming message list for a correct management by
DBusWatch, right?

Still, thanks.


On Wed, 2007-09-19 at 12:12 -0400, Havoc Pennington wrote:
> Hi,
> read_write_dispatch() is an alternative to your own select(). Don't
> use it if you are using DBusWatch.
> If you use DBusWatch, you need to *also* use DBusTimeout. You also
> need to either dispatch() on every iteration of the main loop, *or*
> use set_dispatch_status_function() so you know whether to dispatch.
> set_wakeup_main_function() only matters if you are using threads.
> When a watch is toggled off, you need to remove its file descriptor
> from select(), or you will select() on a descriptor that should not be
> select()'d on. For example, a write watch will be toggled off if there
> are no messages to write.
> When your select() sees that a descriptor is ready, you need to call
> dbus_watch_handle() on the watch corresponding to that descriptor.
> register_object_path() has nothing to do with any of this; it sets up
> handlers to run when you dispatch, if a message is dispatched that
> goes to that object path.
> As it says in the docs, do not use pop_message() in combination with dispatch.
> Conceptually here is what is going on:
>  - there is a list of incoming messages
>  - there is a list of outgoing messages
>  - when the connection file descriptor is ready to write,
> dbus_watch_handle() will write the outgoing messages to the descriptor
> and remove them from the outgoing list
>  - when the connection file descriptor is ready to read,
> dbus_watch_handle() will read the incoming messages from the
> descriptor and add them to the incoming list
>  - when you dbus_connection_dispatch(), each message in turn is
> removed from the incoming list and any handlers that you have
> registered are invoked, such as those from register_object_path()
>  - if you use pop_message() the messages are removed from the incoming
> queue without being dispatched, which is not what you want
> If you are hand-rolling your own C API, remember you also need to
> implement object introspection.
> Havoc
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