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

[rikki cattermole]

On 23/12/2017 11:06 AM, Chris Katko wrote:
> 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.

This isn't related to LDC.
Its just using extern(C) for its linkage abilities.

https://github.com/dlang/druntime/blob/master/src/gc/proxy.d#L90