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

[Phil Bouchard]

On 07/05/2017 08:25 PM, Thiago Macieira wrote:
> On quarta-feira, 5 de julho de 2017 15:31:28 PDT Phil Bouchard wrote:
>> 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.:
>
> What's the advantage compared to the current model where the GC runs
> periodically and frees unused objects before the window is closed?

- Well with root_ptr the behavior is 100% predictable thus you won't 
have these rendering lags at random times.  It happened to me before 
when I had relatively complex listitems using shadows and a nested list 
of pictures for each item; the scrolling speed wasn't constant and I 
think that's a good way to measure this problem.  With root_ptr the 
complexity will remain linear O(n).

- The code of Qt will be much simpler.

- You won't need a separate thread reserved for the garbage collector if 
that is already the case.

- The objects are destroyed is the exact reverse order they were 
constructed thus this will help debugging.


-Phil