Re: [dbus-cplusplus-devel] Setting the callback function and data in dbus-c++ for async calls

[Schmottlach, G. <gle...@ha...>]

It may be better for you to exam this fork of the D-Bus C++ binding where both asynchronous client/server mechanisms are supported:

git://zub.lamer.la/dbus-c++-async.git

I don't believe the "original" C++ binding really supported this.

Also, don't use the C++ binding from different threads because the underlying library (D-Bus Lib) really isn't thread-safe when making asynchronous requests. (See: http://lists.freedesktop.org/archives/dbus/2009-March/011031.html) for more details). It exhibits several race conditions.

The example programs in the above GIT repository are pretty much broken. They compile but won't work so don't use them as a guide. The underlying binding there, however, will work in the asynchronous fashion you desire.

Good luck . . .


-----Original Message-----
From: Freyensee, James P [mailto:jam...@in...] 
Sent: Tuesday, June 09, 2009 7:12 PM
To: dbu...@li...
Cc: Ahmed, Suhail; Benis, Robertino
Subject: [dbus-cplusplus-devel] Setting the callback function and data in dbus-c++ for async calls

Hello:

I am struggling to understand how I could do an asynchronous call using dbus-c++ and was wondering if anyone has any currently working example code, explanation, or a tutorial to help me out.

This is what I know (I believe at least).

For asynchronous calls I need to call the dbus function 

dbus_bool_t  dbus_pending_call_set_notify ( DBusPendingCall *  pending, DBusPendingCallNotifyFunction  function, void *  user_data, DBusFreeFunction  free_user_data  )

This happens when the constructor 

PendingCall::PendingCall(PendingCall::Private *p) : _pvt(p) {}

is called.  

I believe this PendingCall::PendingCall() constructor called when the function in Connection.cpp:

PendingCall Connection::send_async(Message &msg, int timeout)

is called.  

Now I was thinking that a new, unwritten function in object.cpp needs be written as follows that would call send_async():

PendingCall ObjectProxy::_invoke_method_async(CallMessage &call)
{
	if (call.path() == NULL)
		call.path(path().c_str());

	if (call.destination() == NULL)
		call.destination(service().c_str());

	return conn().send_async(call);
}

This is actually pretty similar to 

Message ObjectProxy::_invoke_method(CallMessage &call) {}

in Object.cpp.

The big question is how do I use this dbus-c++ framework to set the (DBusPendingCallNotifyFunction  function, void *  user_data) parameters of the dbus_pending_call_set_notify() function?  I figure I need to set some parameters in the CallMessage object in ObjectProxy::_invoke_method_async() and/or the Message object in the Connection::send_async().  However, I don't know what to do and how to do it.

Second question- is there anything else I am missing that I would need to do to make the callback operation work right in this dbus-c++ framework?

Thank you for the help!

Regards,
Jay Freyensee


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