Wrestling the Garbage Collector.. And loosing..

[Simen Haugen]

Hi.

I'm having a problem with my application using extremly much memory, and the 
only way I'm able to free it is by deleting objects explicitly. I guess I'm 
not understanding the GC right, but I thought that it should free all 
objects without references to it when it's collecting, but my testing below 
shows I'm doing something wrong.

// Test 1
auto str = new char[512];
delete str;
str = new char[512]; // OK. No new allocation

// Test 2
auto str = new char[512];
str = new char[512]; // New memory allocated. GC isn't run. Guess it's 
expected behavior.

// Test 3
auto str = new char[512];
str = null;
str = new char[512]; // New memory allocated. GC isn't run. Guess it's 
expected behavior.

// Test 4
auto str = new char[512];
str = null;
GC.collect;
str = new char[512]; // New memory allocated. Why?

// Test 5
auto str = new char[512];
str.length = 0;
GC.collect;
str = new char[512]; // New memory allocated. Why?

I would have thought Test 4 and 5 shouldn't allocate more memory either as I 
remove the reference (or zero length) and run the GC, but it does.
I would also think Test 2 and 3 should make the GC reclaim memory when it is 
run.

The same applies for classes too, but there I need to explicitly delete all 
members in the destructor also..

And what does GC.minimize actually do? Even if I free an object and run 
minimize, the application still uses the same amout of memory (or at least 
it looks like it)

This is tested with dmd 1.028, tango ca. 0.99.5 (used trunk from back then) 
and win xp.

At this point my program is basically useless because of this. You can run 
it and restart it before the next run, but this limits its use very much. I 
can fix it by explicity deleting objects when I don't need them, but I 
really hope I don't have to.
I'm already using scope everywhere I can, and my tests with those shows it 
helps a lot, but the application will still require a good deal of memory 
and I need to limit this as much as I can.

I really hope someone could enlighten me on the correct usage of the GC 
(I've read the garbage collector documentation and memory article on 
digitalmars and the wikipedia article without getting much smarter)