[fpc-pascal] DBus in GUI application

[Krzysztof]

Thanks for sharing. Your code is working fine. But did you notice
deadlocks (randomly)? For example if I use thread for signals
listening. And then main thread (e.g. button click) want to call some
method from same dbus interface. Even if try to use different
connection by calling dbus_bus_get(DBUS_BUS_SESSION, @err), I'm
getting same pointer. This is my code for method call:

var
  msg: PDBusMessage;
  pending: PDBusPendingCall;
begin

  if conn = nil then Exit;

  // create a new method call and check for errors
  msg := dbus_message_new_method_call('org.mpris.MediaPlayer2.clementine',
// target for the method call
                                      '/Player', // object to call on
                                      'org.freedesktop.MediaPlayer',
// interface to call on
                                      'Next'); // method name
  if (msg = nil) then
  begin
    WriteLn('Message Null');
    Exit;
  end;

  // send message and get a handle for a reply
  if (dbus_connection_send_with_reply(conn, msg, @pending, -1) = 0)
then // -1 is default timeout
  begin
    WriteLn('Out Of Memory!');
    Exit;
  end;
  if (pending = nil) then
  begin
    WriteLn('Pending Call Null');
    Exit;
  end;
  dbus_connection_flush(conn);

  WriteLn('Request Sent');

  // free message
  dbus_message_unref(msg);

  // block until we recieve a reply
  dbus_pending_call_block(pending);

  // get the reply message
  msg := dbus_pending_call_steal_reply(pending);
  if (msg = nil) then
  begin
    WriteLn('Reply Null');
    Exit;
  end;
  // free the pending message handle
  dbus_pending_call_unref(pending);

  // free reply
  dbus_message_unref(msg);
end;

2014-04-05 15:35 GMT+02:00 Luca Olivetti <luca at wetron.es>:
> El 04/04/14 17:46, Krzysztof ha escrit:
>> Hi,
>>
>> DBus documentation give me a headache. Does anyone know solution how
>> to implement DBus in GUI main loop (for signals listening)? I have
>> tried with threads but have two problems:
>> 1. Not all signals are catched (randomly)
>> 2. Deadlock when main thread trying to use dbus methods
>
> Last time (and the only time) I wrote a dbus server was 5 years ago (so
> I used the plain translation of the C api and a now obsolete version of
> dbus), but it was a daemon (not a gui program) with more or less this
> structure:
>
>
> while not terminated do
> begin
>    DbusCycle;
>    { do other things }
> end;
>
> and DbusCycle was managing a non-blocking dbus connection like this:
>
> begin
>   //non blocking read of the next available message
>   if conn<>nil then
>   begin
>     if dbus_connection_get_is_connected(conn)=0 then
>     begin
>        Logger.Error('perdida conexion con bus');
>        conn:=nil;
>     end;
>   end;
>   if conn=nil then ConnectToSystembus;
>   if conn=nil then exit;
>   dbus_connection_read_write(conn,0);
>   msg:=dbus_connection_pop_message(conn);
>   if msg=nil then exit;
>
>   lastfailed:=false;
>
>   // check this is a method call for the right interface & method
>   if (dbus_message_is_method_call(msg,
> 'es.wetron.almacen_tapas.method.Status', 'GetStatus') <> 0) then
>      reply_to_getstatus_call else
>   if (dbus_message_is_method_call(msg,
> 'es.wetron.almacen_tapas.method.Status', 'GetFifo') <> 0) then
>      reply_to_getfifo_call else
>   if (dbus_message_is_method_call(msg,
> 'es.wetron.almacen_tapas.method.Simulation', 'Simulate') <> 0) then
>      reply_to_simulate_call;
>   // free the message
>   dbus_message_unref(msg);
> end;
>
>
> not much help, I know, but it worked (btw: since I also controlled the
> client, in hindsight it was a stupid decision: I could have used
> something more cross-platform like a socket).
>
> Bye
>
>
> --
> Luca Olivetti
> Wetron Automation Technology http://www.wetron.es
> Tel. +34 935883004  Fax +34 935883007
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