Is Phobos's Garbage Collector utterly broken? (Phobos vs Tango)

[Sean Kelly]

Vladimir Panteleev wrote:
> On Wed, 01 Aug 2007 09:08:16 +0300, Vladimir Panteleev <thecybershadow at gmail.com> wrote:
> 
>> I initially wrote it to try to find a memory leak in Tango's GC (which was actually fixed at some point).
> 
> Turns out it's still there, and it's the old "binary data" issue with pointer-searching GCs, which was fixed in D/Phobos 1.001 by making the GC type-aware. Check out the attached sample programs for a simple example - the Tango version can't know there are no pointers in its GrowBuffer's data, and thus leaks like crazy, while the Phobos version stays at 13MB.

The cause of this is somewhat an artifact of the OO design in Tango. 
The underlying buffer being allocated is a byte[], but the reference to 
it is a void[].  The problem occurs when GrowBuffer grows the buffer by 
increasing its length, which causes the buffer to be reallocated as a 
void[].  The reason this is a problem is that neither runtime, Tango or 
Phobos, preserves memory block attributes during a reallocation--they 
both simply key off the type being used to perform the reallocation. 
Obviously, this is a problem, and I've decided to change the behavior in 
Tango accordingly.  It will take some doing and I'm a bit over-busy at 
the moment, but before long the Tango runtime will preserve all block 
attributes on a reallocation.  In essence, this will occur by having the 
runtime call gc_realloc, but before this will work gc_realloc must be 
fixed to handle slices.


Sean