[Issue 8139] Make objects really disposable by addition of "Object finalized" assertion

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https://issues.dlang.org/show_bug.cgi?id=8139

Iain Buclaw  changed:

   What|Removed |Added

   Priority|P2  |P4

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[Issue 8139] Make objects really disposable by addition of Object finalized assertion

[d-bugmail]

http://d.puremagic.com/issues/show_bug.cgi?id=8139


Alex R�nne Petersen a...@lycus.org changed:

   What|Removed |Added

 CC||a...@lycus.org


--- Comment #1 from Alex R�nne Petersen a...@lycus.org 2012-05-24 12:46:56 
CEST ---
The idea in and of itself is not bad. In fact, it would make debugging
wonderfully easy. My only concern is this: Object size. We already store two
words of memory in *every single object header*. This means 8 bytes on 32-bit
and 16 bytes on 64-bit.

Now suppose we added an extra bool field to Object. Not only would the compiler
have to be changed to align fields correctly, but it would also result in
objects eating 12 bytes on 32-bit and 24 bytes on 64-bit (simply because the GC
only power of two allocations or something along those lines).

Now, the memory concern is not a problem for a class like this:

class A
{
bool b;
short s;
}

Obviously we don't need word alignment here, and we could probably optimize
given that. But consider:

class B
{
A a;
}

Suddenly that bool field has to suck an entire machine word's worth of space
for 'a' to be aligned correctly.

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[Issue 8139] Make objects really disposable by addition of Object finalized assertion

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--- Comment #2 from Denis Shelomovskij verylonglogin@gmail.com 2012-05-24 
15:00:11 MSD ---
(In reply to comment #1)
 Now suppose we added an extra bool field to Object.

From Sean Kelly's reply at NG:
 rt_finalize currently nulls out the vtbl pointer, which can server as an 
 isAlive flag if desired.

Link:
http://forum.dlang.org/thread/jo0p3a$aue$1...@digitalmars.com#post-mailman.323.1336157840.24740.digitalmars-d:40puremagic.com

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[Issue 8139] Make objects really disposable by addition of Object finalized assertion

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--- Comment #3 from Alex R�nne Petersen a...@lycus.org 2012-05-24 13:00:51 
CEST ---
In that case, I have no objections to doing this.

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[Issue 8139] Make objects really disposable by addition of Object finalized assertion

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Jacob Carlborg d...@me.com changed:

   What|Removed |Added

 CC||d...@me.com


--- Comment #4 from Jacob Carlborg d...@me.com 2012-05-24 05:10:01 PDT ---
 From Sean Kelly's reply at NG:
  rt_finalize currently nulls out the vtbl pointer, which can server as an 
  isAlive flag if desired.
 
 Link:
 http://forum.dlang.org/thread/jo0p3a$aue$1...@digitalmars.com#post-mailman.323.1336157840.24740.digitalmars-d:40puremagic.com

The vtbl is only needed for virtual methods.

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--- Comment #5 from Alex R�nne Petersen a...@lycus.org 2012-05-24 14:11:06 
CEST ---
It's still set for all objects because it contains a pointer to type info.

(The other machine word is the monitor.)

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