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D.gnu - GDC 4.8: Status of garbage collection and TLS

reply Dan Olson <zans.is.for.cans yahoo.com> writes:
So far I am having fun gradually pushing D into apple ios sim (it runs
i386 not arm).  I am curious though about thread local storage and GC.
I saw older posts about it being an issue and have not seen anything
more on it.  Is it still an issue?  I am doing all this with latest D
git and gcc-4.8-20121028 snapshot.

What I gather is that D TLS vars are not monitored by the collector so
memory can be prematurely collected.  Is that right?

Anyway, so far it is fun to see D code being linked into an ios app
(i386 sim again) and running, making phobos calls.  I build .o or .a
files outside of xcode then drag them in along with libgphobos2.  I
figure if you can call writeln() and see it come out on the xcode gdb
console, then that is progress.  Well, to me anyway.

-- 
dano
Nov 10 2012
parent reply Johannes Pfau <nospam example.com> writes:
Am Sat, 10 Nov 2012 09:12:55 -0800
schrieb Dan Olson <zans.is.for.cans yahoo.com>:

 So far I am having fun gradually pushing D into apple ios sim (it runs
 i386 not arm).  I am curious though about thread local storage and GC.
 I saw older posts about it being an issue and have not seen anything
 more on it.  Is it still an issue?  I am doing all this with latest D
 git and gcc-4.8-20121028 snapshot.
 
 What I gather is that D TLS vars are not monitored by the collector so
 memory can be prematurely collected.  Is that right?

Yes. The GC needs special runtime / compiler support to scan TLS variables and this code has traditionally been buggy / difficult to implement. You can use a simple test to detect the most obvious errors: ------------------------------------------------------------ import std.stdio; import core.memory; class A { string str; void a() { writeln(this.str); } } A var; //TLS variable void main() { var = new A(); var.str = "Hello World"; GC.collect(); //Force collection var.a(); }
Nov 10 2012
parent Dan Olson <zans.is.for.cans yahoo.com> writes:
Johannes Pfau <nospam example.com> writes:
 Yes. The GC needs special runtime / compiler support to scan TLS
 variables and this code has traditionally been buggy / difficult to
 implement.

 You can use a simple test to detect the most obvious errors:

I used your test, but had to make a bunch of objects to get collection to happen. GC *is* reclaiming objects still referenced by TLS and no-TLS (shared). So I will need to look into that some more. Note: this is on osx and I tweaked some of the druntime code to get it to build, so some of this might be my doing. So I guess as a follow up, should I expect the GC to be aware of shared globals, or are there issues there too like thread local?
Nov 10 2012