[Dbus-cxx-users] Hangs (deadlock) with return type of bool

[Fabrizio L. <fa...@lu...>]

I am not sure if this is a bug with dbus-cxx or if I am doing something
wrong. I am trying to use dbus-cxx to send a message to a dbus-python
application (quicktile). Using d-feet I can see that the signature is doCommand
(String command) |-> (Boolean arg_1). In cpp I have created a wrapper class
for the method:

*quickTileProxy.h
<https://github.com/flungo/opensnap-quicktile/blob/feature/dbus/src/quickTileProxy.h>*

#define QT_DBUS_NAME "com.ssokolow.QuickTile"#define QT_OBJECT_PATH
"/com/ssokolow/QuickTile"#define QT_INTERFACE "com.ssokolow.QuickTile"
class quickTileProxy {
    DBus::ObjectProxy::pointer object;public:
    DBus::MethodProxy<bool, std::string>& doCommand;
    quickTileProxy(DBus::Connection::pointer connection);private:

};

*quickTileProxy.cpp
<https://github.com/flungo/opensnap-quicktile/blob/feature/dbus/src/quickTileProxy.cpp>*

#include <dbus-cxx.h>#include "quickTileProxy.h"

quickTileProxy::quickTileProxy(DBus::Connection::pointer connection) :
    object(connection->create_object_proxy(QT_DBUS_NAME, QT_OBJECT_PATH)),
        doCommand(*(object->create_method<bool,std::string>(QT_INTERFACE,"doCommand")))
{

}

This is instantiated with:

*opensnap.cpp:181
<https://github.com/flungo/opensnap-quicktile/blob/feature/dbus/src/opensnap.cpp#L181>*

qt_proxy = new quickTileProxy(connection);

and doCommand is called with the line:

*opensnap.cpp:40
<https://github.com/flungo/opensnap-quicktile/blob/feature/dbus/src/opensnap.cpp#L40>*

rtn = qt_proxy->doCommand(args);

The command runs successfully on the quicktile daemon and the action is
performed however at this point the code hangs. Using gdb I have traced the
point that the code hangs to between lines 127 and 128 of
/usr/include/dbus-cxx-0.8/dbus-cxx/methodproxy.h:

ReturnMessage::const_pointer retmsg = this->call( _callmsg );
T_return _retval;

The disassembly shows that it is in a __lll_lock_wait and would appear to
be deadlocked. The full disassembly:

__lll_lock_wait()
__lll_lock_wait+28: mov    %edx,%eax
__lll_lock_wait+30: xchg   %eax,(%rdi)
__lll_lock_wait+32: test   %eax,%eax
__lll_lock_wait+34: jne    0x7ffff2eb4115 <__lll_lock_wait+21>
__lll_lock_wait+36: pop    %rdx
__lll_lock_wait+37: pop    %r10
__lll_lock_wait+39: retq

I am currently using *aur/dbus-cxx 0.8.0-2* (which I think is the latest)
from the Arch Linux AUR. If you would like to browse or download the full
source code then it is available from GitHub
<https://github.com/flungo/opensnap-quicktile/tree/feature/dbus>. Hopefully
someone is able to shed some light on what is going wrong?

I don’t *think* there is an issue with the python side of things as I can
execute fine with d-feet but the source for this is also available on GitHub
<https://github.com/ssokolow/quicktile>.

Many Thanks,
Fabrizio Lungo

http://yours.sincere.ly/flungo/ <http://sincere.ly/flungo/>
​