Threads, shread and TLS

[Adam Conner-Sax]

Thanks!

It's not really about correctness as much as trying to understand how these
different storage classes work.  I understand that there is only one foo object.
I wanted to see which parts are thread-local and which are shared and how the
constructors work.

I'm working (way over my head) on a more complex threading issue and I realized
that I didn't quite understand the storage classes and constructors. Now I get it
a bit more.

By "untagged sharing" do you mean the "a" variable which is shared in the sense
that all threads see the same copy but does not have storage class "shared"?  Yes,
that confuses me too.  Should it be an error?

I have never dealt with bugzilla but I will try to figure out how to do what you
ask :)

Thanks again.

Adam



== Quote from Steven Schveighoffer (schveiguy at yahoo.com)'s article
> On Fri, 07 Jan 2011 09:55:33 -0500, Adam Conner-Sax
> <adam_conner_sax at yahoo.com> wrote:
> > == Quote from Adam Conner-Sax (adam_conner_sax at yahoo.com)'s article
> >> So, I thought I sort of understood "shared" and now I think I don't.
> >> If I have a class:
> >> class foo {
> >>   int x;
> >>   static int y;
> >>   shared static int z;
> >> }
> >> So x is one instance per class and is thread-local?
> >> y is one instance per thread?
> >> z is one instance per application, i.e., global?
> >> If that's true (and I realize it might not be), and I want to
> >> initialize these
> >> variables in constructors, how does that work?
> >> I think
> >> class foo {
> >> ...(as before)
> >> this() { x = 2; } // ok
> >> static this() { y = 3; } // is this called once per thread?
> >> shared static this() { z = 3;} // also, okay, called before main
> >> }
> >> but I don't understand what happens with threads and the "static this"
> >> constructor.  How/when are the thread-local copies constructed?  How do
> >> you
> >> initialize/construct the thread-local static data?
> >> Thanks!
> >> Adam
> >
> > Nevermind.  Answered myself with the following:
> >
> > import core.thread;
> > import std.c.stdio;
> >
> > class foo {
> >
> >   int a;
> >   shared int b;
> >
> >   static int x;
> >   shared static int y;
> >   shared static int[] arr1;
> >   shared static int[] arr2;
> >
> >   this() { a = 1; b=10; }
> >   static this() { x=100; arr1 ~= x; }
> >   shared static this() { y=1000; arr2 ~= y;  }
> >
> >   static void A() { x++; y++; }
> >   void B() { a++; b++; }
> >   void report() {
> >     printf("a=%i; b=%i; x=%i; y=%i; arr1.length=%i;
> > arr2.length=%i\n",a,b,x,y,arr1.length, arr2.length);
> >   }
> > }
> >
> > void main()
> > {
> >   auto f = new foo();
> >   void call_foo_functions() { f.A(); f.B(); f.report(); }
> >   auto tg = new ThreadGroup();
> >   foreach (k; 0..3) {
> >     auto t = new Thread(&call_foo_functions);
> >     tg.add(t);
> >     t.start();
> >   }
> >   tg.joinAll();
> >   printf("back in main: ");
> >   f.report();
> >  }
> >
> > which output:
> >
> > a=2; b=11; x=101; y=1001; arr1.length=2; arr2.length=1
> > a=3; b=12; x=101; y=1002; arr1.length=2; arr2.length=1
> > a=4; b=13; x=101; y=1003; arr1.length=3; arr2.length=1
> > back in main: a=4; b=13; x=100; y=1003; arr1.length=3; arr2.length=1
> >
> >
> > which all makes sense (to me) except a.  Why is a acting global?  Is it
> > since it
> > isn't static so it belongs to the class and there is only one copy of
> > the class?
> > Then what makes a and b different?
> OK, so here is what is happening :)
> call_foo_functions is a delegate, which means it has a frame pointer to
> the main function.  So all three threads' f is the *same* f (the one
> defined in main()).
> I would suggest that you move call_foo_functions outside main, and
> instantiate an additional f *inside* the function.  This would be more
> correct.
> Incidentally, it appears that this allows untagged sharing (i.e. sharing
> data that isn't tagged with shared)  I wonder if this issue has been
> reported before?  Sean?
> >
> > Also, though maybe it's obvious to everybody else, I think the docs
> > should explain
> > someplace that "static this()" gets called once *per thread*.  Maybe I
> > just missed it.
> >
> Yes, the documentation is out of date.  Could you file a bugzilla report
> on this?
> -Steve