dbus glib + pthreads

[John Palmieri]

----- "Kees Jongenburger" <kees.jongenburger at gmail.com> wrote:

> On Sat, Oct 31, 2009 at 12:25 AM, John Palmieri <johnp at redhat.com>
> wrote:
> > You always need to use private connections in different threads
> otherwise one thread can starve the buffer or make calls to code
> across the thread boundary.
> 
> I am trying to understand what this mean.
> 
> is having a private connection  the same as having
> a private variable and calling dbus_g_bus_get(DBUS_BUS_SYSTEM,
> &error);?

No, dbus_g_bus_get returns a pointer to a singleton for each type of supported bus (system and session).  It will always be the same shared connection. From the docs:

Returns a connection to the given bus. The connection is a global variable shared with other callers of this function.

> or do I need to go lower like here
> http://dbus.freedesktop.org/doc/api/html/group__DBusConnection.html
> and call dbus_connection_open_private ?

The Glib docs don't seem to have private connections so you would have to use dbus_bus_get_private and dbus_connection_setup_with_g_main to get the functionality you want.  

> >
> > ----- "Kees Jongenburger" <kees.jongenburger at gmail.com> wrote:
> >
> >> Hello I am having difficulties using dbus in combination with a
> >> threaded program.
> >>
> >> Basically I have two threads one where I want to listen to
> incoming
> >> dbus calls and one thread that will call other dbus services. This
> >> second thread
> >> will for example also perform a long running download or call
> other
> >> dbus services (also using glib). My main thread uses the glib main
> >> loop while my second thread
> >> simply performs his tasks end then dies.
> >>
> >> I am experiencing random crashes when in the seconds thread I
> start
> >> performing dbus glib method calls.I am  dbus_threads_init_default
> but
> >> clearly this is not enough
> >> What else am I missing?
> >>
> >> -Do I have to use the same dbus connection for booth threads or
> not?
> >> -Do I have to use a private dbus connection?
> >> -Should I run two mainloops?
> >>
> >> I am currently quite clueless. Here is such a backtrace for
> example
> >> 0x00007f91c0a85b6f in g_main_context_query () from
> >> /usr/lib/libglib-2.0.so.0
> >> (gdb) bt
> >> #0  0x00007f91c0a85b6f in g_main_context_query () from
> >> /usr/lib/libglib-2.0.so.0
> >> #1  0x00007f91c0a8a627 in ?? () from /usr/lib/libglib-2.0.so.0
> >> #2  0x00007f91c0a8adad in g_main_loop_run () from
> >> /usr/lib/libglib-2.0.so.0
> >> #3  0x0000000000402a13 in run_main_loop () at
> >> echo_calling_service_threaded.c:202
> >> #4  0x0000000000402aee in main (argc=2, argv=0x7fffc95d6738) at
> >> echo_calling_service_threaded.c:234
> >>
> >>
> >> I created sample code and "demo" that shows the problem I am
> >> experiencing you can get it from
> >> http://github.com/keesj/dbus_glib_pthread
> >>
> >> We have a EchoService that can echo strings. We also have a
> >> EchoCallingService that can be called to call the
> >> EchoService a certain number of time. The EchoCallingService on
> one
> >> side accepts incomming requests to call the
> >> EchoService a given number of times.
> >> At the same time it will be calling the EchoService itself. We
> want
> >> to
> >> use thread to model this and want one thread that
> >> listens for incoming dbus messages(this is the main thread)
> >> and one thread that performs the calls to the EchoService.
> >>
> >>
> >>
> >> The flow of the calls should look something like this.
> >> test/test_echo_calling_service test 1200
> >>   |
> >>   |
> >>   |--callEcho(test,1200)->echo_calling_service_threaded(incomming
> >> end)
> >>                            |
> >>                            |
> >>                            |- start or
> >> notify--->echo_calling_service_threaded(sending end)
> >>   |<-----------------------|                     |
> >>                                                  |
> >>                                                  |--1200 times
> >> echo(test)-->echo_service
> >>
> >>       |
> >>
> >> |<--------------------------|
> >>
> >>
> >> How to test the current code:
> >> 0) compile the code run make
> >> 1) modify and copy the configuration file in data/
> >> (echo_calling_service.conf and echo_service.conf) to
> >> /etc/dbus/system.d the user name needs changing.
> >> 2) run export LD_LIBRARY_PATH=alib
> >> 3) start the echo_service ./echo_service -v &
> >> 4) run ./echo_client and see it is possible to call the echo
> service
> >> 10000 times witout problem
> >> 5) start the echo calling service ./echo_calling_service_threaded
> -v
> >> &
> >> (possibly running this under gdb)
> >> 6) start the test -> execute ./test/test_echo_calling_service test
> >> 1200 a number of times
> >>
> >> Expected outcome the service works like charm and doesn't eat
> memory
> >> or crash
> >>
> >> Actual outcome:
> >> the echo_calling_service_threaded crashed in unpredictable ways
> >> _______________________________________________
> >> dbus mailing list
> >> dbus at lists.freedesktop.org
> >> http://lists.freedesktop.org/mailman/listinfo/dbus
> >
> > --
> > --
> > John (J5) Palmieri
> > Software Engineer
> > Red Hat, Inc.
> >

-- 
--
John (J5) Palmieri
Software Engineer
Red Hat, Inc.