[Development] Qt 5.9's new garbage collector documentation? + root_ptr

[Phil Bouchard]

On 07/05/2017 02:29 AM, Thiago Macieira wrote:
> On Tuesday, 4 July 2017 21:03:14 PDT Phil Bouchard wrote:
>> Hi,
>>
>> I read Qt 5.9 is using a new garbage collector that is more predictable.
>>   First good job and second I was wondering if there is any
>> documentation on that garbage collector in question.
>
> That might be in the QML engine VM. The rest of Qt does not use garbage
> collectors.
>
>> I guess if there is any interests to make the garbage collector
>> perfectly deterministic then root_ptr could be relatively easily
>> integrated at this stage.
>
> How does root_ptr work with JavaScript semantics?

(So as you can see in the file attached I have revamped my Javascript 
skills.  And so with the QML.)

But first of all root_ptr is as you know a "set" of reference counted 
pointers, where the "set" vanished from existence when the destructor of 
the associated root_ptr is called.

For example in HTML we could have 1 root_ptr for each HTML page and when 
this page is destroyed then the root_ptr guarantees all associated nodes 
will be destructed as well.  When I refer to a node I mean the 
representation of an atomic variable or a function in Javascript which 
is pointed to by a reference counted pointer.  So you can have all the 
mess you want in Javascript, when the page is destroyed then all memory 
associated to that page is freed.

It's the same thing with QML and its windows.  When a window is 
destroyed then all associated variables will vanish as well, cyclic or 
not.  From my experience, the only way a window can return a value is 
either by sending a signal with its parameters passed by value or by 
storing them in some local database.  But the parent shouldn't have any 
pointer connection of QML / Javascript type with its child window 
(downstream) otherwise it's bad programming.  Ex.:

            Window 1
            ---------
            |       |   Window 2
            |       |     ---
            |  root_ptr2->| |
            |       |     ---
root_ptr1->|       |
            |       |   Window 3
            |       |     ---
            |  root_ptr3->| |
            |       |     ---
            ---------

Here when root_ptr2 gets deleted from the list of Window 1's childs then 
everything inside Window 2 will get destroyed.  The same for root_ptr3 / 
Window 3.  If root_ptr1 gets destroyed then the whole app is guaranteed 
to vanish.


Regards,
-Phil
https://github.com/philippeb8/root_ptr
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