Re: Garbage Collector : Ignoring a reference

[Guillaume Piolat via Digitalmars-d-learn]

On Tuesday, 26 April 2016 at 09:07:59 UTC, Begah wrote:
I am trying to create an asset manager for my textures. I had 
the idea ( it may be a wrong idea ) to create a hashmap of my 
textures with a string as the key. When the program request a 
texture, it firts check if it is in the hashmap and then 
returns if it is :


Texture[string] textures;

Texture loadTexture(string filename) {
  if(filename in textures)
return textures[filename]
  else
// Load image and put it in hashmap
}

Warning : I haven't tested if it actually doesn't work, but 
thinking about it, i think it should not.
My problem is that i return a reference of the texture to the 
program, but i keep one to myself and i want to free the 
texture if my program isn't using it anymore ( no more 
reference to it ). The problem i see, is that i will always 
have atleast one reference to the texture in my hashmap, but i 
want the garbage collector to ignore that reference and to free 
the texture if there are no more references anywhere in my 
program ( except in the hashmap ).


How could i tell the garbage collector to ignore the reference 
in the hashmap and to free it if there isn't any other 
reference that in my hashmap?


You should avoid to rely on the garbage collector to free 
non-memory resources anyway. This is accidental correctness. You 
are not guaranteed to get called by the GC, or by the appropriate 
thread.


You can call .destroy() on these textures when in the texture 
manager destructor.

Re: Garbage Collector : Ignoring a reference

[Namespace via Digitalmars-d-learn]

On Tuesday, 26 April 2016 at 09:07:59 UTC, Begah wrote:
I am trying to create an asset manager for my textures. I had 
the idea ( it may be a wrong idea ) to create a hashmap of my 
textures with a string as the key. When the program request a 
texture, it firts check if it is in the hashmap and then 
returns if it is :


Texture[string] textures;

Texture loadTexture(string filename) {
  if(filename in textures)
return textures[filename]
  else
// Load image and put it in hashmap
}

Warning : I haven't tested if it actually doesn't work, but 
thinking about it, i think it should not.
My problem is that i return a reference of the texture to the 
program, but i keep one to myself and i want to free the 
texture if my program isn't using it anymore ( no more 
reference to it ). The problem i see, is that i will always 
have atleast one reference to the texture in my hashmap, but i 
want the garbage collector to ignore that reference and to free 
the texture if there are no more references anywhere in my 
program ( except in the hashmap ).


How could i tell the garbage collector to ignore the reference 
in the hashmap and to free it if there isn't any other 
reference that in my hashmap?


Texture[string] textures;

Texture* loadTexture(string filename) {
  if(filename in textures)
return [filename]
  else
// Load image and put it in hashmap
}

Texture* tex = loadTexture(...);

Re: Garbage Collector : Ignoring a reference

[Marco Leise via Digitalmars-d-learn]

Am Tue, 26 Apr 2016 13:35:37 +
schrieb Begah :

> When the screen switches to another screen ie from menu to the 
> game,
> I want that the "button.png" texture is automaticly destroyed by 
> the gc.

My ideological point of view is that you must not use
non-deterministic garbage collection for resources. Neither
for files, GUI widgets or textures. The garbage collector
cannot look past its own confined environment (heap memory
allocated by the D program and loaded D libraries) and will
not have enough information to tell if the process is running
out of file handles, backing buffer for widgets or texture
memory on the graphics card. It only takes action, when its own
heap is filling up or when you manually call GC.collect().
All the convenient 100% GC languages from Java to Python
require the user to call ".close()" for files,
".dispose()/.Destroy()" for widgets, etc.
Reference counting is the correct approach. It makes using
external resources safe and convenient by removing the need
for manual lifetime management. Cyclic references cannot
exist in the D code in this scenario.

The texture constructor:
- sets ref count to 1
- adds texture to hash map
The copy constructor:
- increments the ref count
The destructor:
- decrements the ref count
- if ref count reaches 0:
  - removes the texture from the hash table
  - destroys the texture data

-- 
Marco

Re: Garbage Collector : Ignoring a reference

[ciechowoj via Digitalmars-d-learn]

Thus, i need a way to tell the gc to ignore the reference ( or 
something similar ) in that hashmap.


So, having pointer that doesn't hold a reference isn't that hard 
(store it in memory region that is unreachable to gc), but don't 
you need a way to tell if that pointer ins't dangling, beyond 
initial problem?

Re: Garbage Collector : Ignoring a reference

[ag0aep6g via Digitalmars-d-learn]

On 26.04.2016 15:35, Begah wrote:

Nothing will reload.

An example :
I load a texture "button.png" in a class and draw it to the screen,
When the screen switches to another screen ie from menu to the game,
I want that the "button.png" texture is automaticly destroyed by the gc.
But this will never happen because i still have a reference to it in my
hashmap.
Thus, i need a way to tell the gc to ignore the reference ( or something
similar ) in that hashmap.


How would you prevent reads of that now-invalid element of the hashmap?

Re: Garbage Collector : Ignoring a reference

[Begah via Digitalmars-d-learn]

On Tuesday, 26 April 2016 at 13:01:26 UTC, ciechowoj wrote:

On Tuesday, 26 April 2016 at 09:07:59 UTC, Begah wrote:
How could i tell the garbage collector to ignore the reference 
in the hashmap and to free it if there isn't any other 
reference that in my hashmap?


You could always zero the reference in the hashmap, as it won't 
be valid after reload anyway...


Nothing will reload.

An example :
I load a texture "button.png" in a class and draw it to the 
screen,
When the screen switches to another screen ie from menu to the 
game,
I want that the "button.png" texture is automaticly destroyed by 
the gc.
But this will never happen because i still have a reference to it 
in my hashmap.
Thus, i need a way to tell the gc to ignore the reference ( or 
something similar ) in that hashmap.

Re: Garbage Collector : Ignoring a reference

[ciechowoj via Digitalmars-d-learn]

On Tuesday, 26 April 2016 at 09:07:59 UTC, Begah wrote:
How could i tell the garbage collector to ignore the reference 
in the hashmap and to free it if there isn't any other 
reference that in my hashmap?


You could always zero the reference in the hashmap, as it won't 
be valid after reload anyway...

Re: Garbage Collector : Ignoring a reference

[Alex Parrill via Digitalmars-d-learn]

On Tuesday, 26 April 2016 at 09:07:59 UTC, Begah wrote:
I am trying to create an asset manager for my textures. I had 
the idea ( it may be a wrong idea ) to create a hashmap of my 
textures with a string as the key. When the program request a 
texture, it firts check if it is in the hashmap and then 
returns if it is :


[...]


What you want are "weak references". I don't think D supports 
them yet.

Garbage Collector : Ignoring a reference

[Begah via Digitalmars-d-learn]

I am trying to create an asset manager for my textures. I had the 
idea ( it may be a wrong idea ) to create a hashmap of my 
textures with a string as the key. When the program request a 
texture, it firts check if it is in the hashmap and then returns 
if it is :


Texture[string] textures;

Texture loadTexture(string filename) {
  if(filename in textures)
return textures[filename]
  else
// Load image and put it in hashmap
}

Warning : I haven't tested if it actually doesn't work, but 
thinking about it, i think it should not.
My problem is that i return a reference of the texture to the 
program, but i keep one to myself and i want to free the texture 
if my program isn't using it anymore ( no more reference to it ). 
The problem i see, is that i will always have atleast one 
reference to the texture in my hashmap, but i want the garbage 
collector to ignore that reference and to free the texture if 
there are no more references anywhere in my program ( except in 
the hashmap ).


How could i tell the garbage collector to ignore the reference in 
the hashmap and to free it if there isn't any other reference 
that in my hashmap?