[DMD or LDC] Is it possible to get the GC to print to stdout when it collects?

[Chris Katko]

I'm having a strange stuttering issue in my game prototype. I use 
GC allocations wildly for the heck of it at the moment--with 
eventual plans to remove them.

However, I'm not positive it's the GC that's the problem, and if 
so, I want to know exact lengths of time and frequency.

Currently, the game will freeze for up to even half a second or 
more (but pretty rarely of 15+ seconds apart or more) but 
strangely... I'm using stopwatch's to track the logic and drawing 
code's elapsed times and ... those stopwatches don't appear to 
show the frozen time. Maybe my time code is incorrect somewhere 
but I need to be sure.

The hallmarks of GC are there because it "seems" to occur more 
often / worse when I'm low on RAM.

In LDC2, I saw import/core/memory.d -> gc.collect() which calls 
gc_collect (a C function)

However, adding a printf in there doesn't appear to print, so I'm 
guessing that gc.collect is only for users and not actually 
called by any internal lib functions? So my next thought is, to 
get a full source distribution, and recompile DMD or LDC2 from 
source after finding that C source file and adding a printf in 
there.

I doubt a single printf (or some static string equivalent without 
formatting overhead) would take that much time compared to a 
complete garbage collection so I don't think it would skew the 
results enough to useless. The big thing to check here is if 
these "freezes" are directly related to garbage collections, or 
some other oddity.