Order of Destruction in Garbage Collector

[DanielSchick]

Hej hej,

first of all I want to give a big thanks to the developers of G#. GREAT WORK!

But I have a question concering the Garbage Collector of G#.

I have the following situation:

A ConfigObject can read and write parameters from a XML-file.

When it is finally destroyed the data is actually written to disk.

This works perfectly.

Now I have DeviceObjects which need to read and write their parameters to that ConfigObject.

So the ConfigObject is a property of each DeviceObject.

In the Destructor of a DeviceObject it hands its parameters to the ConfigObject.

And when the ConfigObject destructs it should write the parameters to the XML-File, which works in this order.

Now the problem is:

In my application I open the same ConfigObject (Singelton) multiple times in different DeviceObjects and at first in the MainApplication itself.

When I close the MainApplication the GarbageCollector starts to destroy the ConfigObject at first, since it was initialized before the DeviceObjects. The G# Debugger shows that there are multiple users of the ConfigObject but the GarbageCollector still continues to destroy first the ConfigObject until it is finally destroyed.

Finally the DeviceObjects are destroyed which write their parameters to the ConfigObject in their destructor. But the ConfigObject is then already destructed and the parameters are not written to disk!

So the G# Garbage Collector dosn't first destroy the DeviceObjects, although they hold a reference to the ConfigObject.

I hope you see my problem, that the GarbageCollector doesn't change its order of destruction when I have somehow nested references.

I know that I can do some workarounds to solve that problem, but my idea is, that the framework could handle that issue for me, which would made development much easier.

I would be very thankful to any of your ideas and comments, since I am not a that experienced LV programmer...

Cheers

Daniel

[Mattias_Ericsson]

Hi Daniel,

We really appriate that you like the G# Framework! As I understand it, you are not using the Destroy method of the DeviceObject directly, but let the garbage collector (GC) do the work. However, the GC doesn't take any care of aggregation or any kind of usage of the objects, just trying to kill them in the following order:

1) Sort by class, classes with the "oldest" first object created

2) Sort by object, the "oldest" object dies first.

This is exactly the behaviour you describe above. If you compare how the GC work in e.g C#, there you have no guarantee when the destructor of the objects executes, but aggregated objects will not be GC in the wrong order, since the aggregating object is still holding a reference to its aggregates and your situation above would have worked. This would be quite hard to implement in G#, but not impossible. I will take a look at it until the next major release of the framework. This is a really good suggestion!

The best way (or workaround) to solve your problem could be made in two ways:

1) Run the GC twice, first time with the "DeviceObjects.lvclass" as input parameter to "full class name", the run the GC again without any input. This will force GC to first kill all DeviceObjects, then the rest of them. Notice, if you have your classes in a lvlib, you have to specify the complete name space as full class name.

2) You could just use the Destroy method and loop and kill each of the DeviceObjects before you use the GC.

Regards,

Mattias

[DanielSchick]

Hej Matthias,

thank you for your fast reply. So, now I know, that it was not a mistake of mine, and I think I will do a work-around.

But I think, in order to overcome the destructor-problem I will not explicitly destroy the DeviceObjects in my MainApplication or add extra code there.

Since I am waiting now for your new release I will adjust my set-methods of the DeviceObjects. So the parameters are handed to the Config already by setting them and not when the DeviceObject destructs. Thereby I only have to modify the class methods later and not the code of the MainApp, when there might be a fix in the next release.

By the way, is there any relase date for the new major release?

Cheers,

Daniel

[Mattias_Ericsson]

Hi,

Ok, sounds a good way of solving it. The release date is not yet set, but I had a look at the Garbage Collector issue and have now a working beta. I must test it a bit more first, especially tricky is when there are circular dependencies (objects have references to each other), but I think I got a working solution. I guess I could do a minor release first just including this new behavior of GC. Give me a week or two and I could release G# IDE 1.2.5.

Regards,

Mattias

[DanielSchick]

Alright, I am looking forward to this...

...

And it works like a charm!

Thank you very much!

Daniel