[Issue 1804] Severe GC leaks with repetitive array allocations

[d-bugmail at puremagic.com]

https://d.puremagic.com/issues/show_bug.cgi?id=1804


safety0ff.bugz <safety0ff.bugz at gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |RESOLVED
                 CC|                            |safety0ff.bugz at gmail.com
         Resolution|                            |FIXED


--- Comment #9 from safety0ff.bugz <safety0ff.bugz at gmail.com> 2014-02-14 20:07:41 PST ---
(In reply to comment #8)
> I'm reopening this, because I noticed the problem
> (core.exception.OutOfMemoryError after about 20000 iterations) still exists on
> Windows XP 32bit with latest dmd 2.063. Works ok on Linux though.

The original bug was fixed. Your observation is due to false pointers, consider
the code at the end of this comment:
When version = A is enabled, the false pointers cause memory to be considered
alive much longer, exactly like the code in the OP.
When version = A is disabled, only pointers to the start of the memory block
make the GC consider it "alive," so less memory is retained by false pointers.
-------------- Begin Code ----------------------
import std.stdio;
import core.memory;

version = A;

void main()
{
    for(uint i=1; i!=0; i++)
    {
version(A) auto tmp = cast(char*)GC.malloc(i * 1024, GC.BlkAttr.NO_SCAN);
else       auto tmp = cast(char*)GC.malloc(i * 1024, GC.BlkAttr.NO_SCAN |
GC.BlkAttr.NO_INTERIOR);

        for (uint j = 0; j<i*1024; j+=1024)
            tmp[j] = 0; // poke the memory
        if(i % 1_000 == 0)
            writefln("%d iterations, roughly %.1f MiB", i, i/1024.0);
    }
}
-------------- End Code -------------------------

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