http://d.puremagic.com/issues/show_bug.cgi?id=3523

           Summary: Fiber is not garbage collected properly
           Product: D
           Version: 2.032
          Platform: Other
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: druntime
        AssignedTo: sean@invisibleduck.org
        ReportedBy: baryluk@smp.if.uj.edu.pl


--- Comment #0 from Witold Baryluk <baryluk@smp.if.uj.edu.pl> 2009-11-18 19:50:33 PST ---
Program below leaks memory.

import core.thread;
import std.stdio;

lass DerivedFiber : Fiber {
  this() { super( &run );  }
 private void run() { Fiber.yield(); }
}

import core.memory : GC;

void main() {
    foreach (i ; 1 .. 1000000) {
        Fiber derived = new DerivedFiber();
        derived.call();
        GC.collect(); // doesn't work
    }
}

Manual destruction of fiber works:
              delete derived;
        }
and then it doesn't leek.

chaning Fiber to "scope" also works (just like delete befor "}"

I know it have something to do with similarity of Fiber to thread, that Fiber have own pool of root variables and own stack. But if Fiber is not running, and it is not accesible by any reference from any Thread, then it is imposible to resume its operation by call(), so also it's root variables and stack is not avaible, so it can (and should?) be garbage collected.

I have code which creates few fibers, do milions call/yield operations, then destroy fibers, and recreat new ones, for and essentially repeats. I was hoping this would not leak memory. Unfortonetly it is.

I this is intended behaviour it should be documented somewhere.

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--- Comment #1 from Witold Baryluk <baryluk@smp.if.uj.edu.pl> 2009-11-18 19:56:25 PST ---
If one will not call derived.call() (so leaving Fiber in TERM state, and never
running it at all) it will be properly collected.

Adding after derived.call(), a derived.reset() to make it back to TERM state,
doesn't help (still it is not collected).

Adding second derived.call(), after first one, will make collect() to work
correctly.

So i can assume it run() method terminates correctly and underlaying stack is destroyed, object is properly destructed in colletion phase.

Essentially my problem is because my Fibers doesn't terminate at all they "yield" infinitly (saving some auxilary data in fields of some objects, so this data can be used outside of yield, essentiall in thread which called call), but i want to terminate them automatically (when they are not referenced by any thread or other Fiber) if needed.

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Sean Kelly <sean@invisibleduck.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED


--- Comment #2 from Sean Kelly <sean@invisibleduck.org> 2009-11-19 07:28:26 PST ---
Hm... that's tricky.  The fiber implementation needs to hold a reference to the fiber on its stack for context switching, and that's the reference that is keeping the fiber alive.  I'll play with the stack pointers a bit and see if things work if I exclude that reference from the GC scan.

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--- Comment #3 from Witold Baryluk <baryluk@smp.if.uj.edu.pl> 2009-11-24 16:05:22 PST ---
I "solved" my problem by changin one of my base clases from:

abstract class AGenerator : Fiber {
protected:
        this(void delegate() dg) {
                super(dg);
        }
}


To:
abstract class AGenerator {
private:
        Fiber x;

protected:
        this(void delegate() dg) {
                x = new Fiber(dg);
        }
        ~this() {
                delete x;
        }
public:
        void call() {
                x.call();
        }
        void yield() {
                x.yield();
        }
        Fiber.State state() {
                return x.state;
        }
}

And it magically started working correctly (Fibers are properly destroyed).

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--- Comment #4 from Witold Baryluk <baryluk@smp.if.uj.edu.pl> 2009-11-25 05:53:40 PST ---
No, sorry i made mistake. Even after change it is not garbage collected. Which is normal, because this Fiber is running some method from this object (namly method named void iter() ), so this object (AGenerator) is still referenced by Fiber, and it's destructor can't be called. So probably only way to call destructor will be to separate this into two classes, which is referenced by delegate from class A, and second which is used only for calling from outside of fiber.

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--- Comment #5 from Witold Baryluk <baryluk@smp.if.uj.edu.pl> 2009-11-25 06:11:41 PST ---
Ok, i now i solved it using kind of hack:

/** This class is written because Fiber's are not correctly garbage collected
*/
class GenWrap(T : AGenerator, T2) {
    private T x; /// T derives from AGenerator which derives from Fiber
public:
    this(T x_) { x = x_; }
    ~this() { delete x; }
    T2 getNext() { return x.getNext(); }
    T o() { return x; } // don't assign return value to any variable which can
live longer than this object
}

This is hack, because it can destroy Fibers which are still referenced somewhere. So All my direct usages of variables of type T, must be changed to use GenWrap.o(), to be sure that delete x inside destructor is safe.

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dawg@dawgfoto.de changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dawg@dawgfoto.de


--- Comment #6 from dawg@dawgfoto.de 2012-02-14 05:44:18 PST ---
I think this works now, doesn't it?

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--- Comment #7 from Witold Baryluk <baryluk@smp.if.uj.edu.pl> 2012-02-14 10:20:42 PST ---
(In reply to comment #6)
> I think this works now, doesn't it?

If you think so, I will test it shortly and report back.

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--- Comment #8 from Witold Baryluk <baryluk@smp.if.uj.edu.pl> 2012-02-14 20:53:05 PST ---
Still same problem in 2.052. :(

Will check tomorrow 2.057, or 2.058 if it will be released.

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--- Comment #9 from Witold Baryluk <baryluk@smp.if.uj.edu.pl> 2012-02-14 21:12:50 PST ---
(In reply to comment #8)
> Still same problem in 2.052. :(
> 
> Will check tomorrow 2.057, or 2.058 if it will be released.

Well, it looks 2.058 is already available. I installed it (again 32-bit Linux), and program leaks - it starts at about 14MB of virtual memory usage, 4MB or RAM usage, and both grows about 1MB per second, after minute giving about 100MB, and constantly growing.

So problem is still present.

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