Tracking memory usage

[Cauterite via Digitalmars-d-learn]

On Sunday, 7 August 2016 at 00:28:40 UTC, Alfred Pincher wrote:
> this is a very nice feature. I hope D has something similar?

If you want to implement that kind of allocation tracking you'll 
probably want to use gc_getProxy()+gc_setProxy(). They're global 
C functions you can access by declaring:
extern(C) gc.gcinterface.GC gc_getProxy() nothrow;
extern(C) void gc_setProxy(gc.gcinterface.GC);

First call gc_getProxy() to get the real GC instance and save it 
somewhere.
Then call gc_setProxy() with your object implementing the GC 
interface functions, and in each function forward to the 
corresponding function of the real GC instance, after any 
statistic-gathering code you want run.

Something like this:

__gshared GC RealGcInstance = gc_getProxy();
__gshared GC MyProxy = new class GC {
	// ...
	extern(C) void gc_free(void* Ptr) nothrow {
		printf("freeing pointer %x\n", Ptr); // or whatever
		return RealGcInstance.free(Ptr);
	};
	// ... etc.
};
gc_setProxy(MyProxy);

I haven't tested this method myself, but it will probably work. 
Refer to 
https://github.com/dlang/druntime/blob/master/src/gc/proxy.d and 
https://github.com/dlang/druntime/blob/master/src/gc/gcinterface.d

Also remember that you can't invoke the GC from inside the proxy 
functions. Using helper functions marked @nogc might make it 
easier to avoid.