The code below:
    module used;

    import std.stdio;

    class ClassA {
        this()  { writeln("A ctor"); }
        ~this() { writeln("A dtor"); }
    }

    static this()  { writeln("used.sctor"); }
    static ~this() { writeln("used.sdtor"); }

    void main() {
        auto a = new ClassA();
    }
produces the following output (DMD v2.049):
    used.sctor
    A ctor
    used.sdtor
    A dtor

The question is: should the module be allowed to be unloaded before all module-level objects/structures are destructed/unloaded?

On Tue, 05 Oct 2010 23:25:36 +0200, vano wrote:

> The code below:
>      module used;
> 
>      import std.stdio;
> 
>      class ClassA {
>          this()  { writeln("A ctor"); }
>          ~this() { writeln("A dtor"); }
>      }
> 
>      static this()  { writeln("used.sctor"); } static ~this() {
>      writeln("used.sdtor"); }
> 
>      void main() {
>          auto a = new ClassA();
>      }
> produces the following output (DMD v2.049):
>      used.sctor
>      A ctor
>      used.sdtor
>      A dtor
> 
> The question is: should the module be allowed to be unloaded before all module-level objects/structures are destructed/unloaded?


I'm no expert on this, but I think it has to be that way.  Consider this:

  class Foo { ... }
  Foo foo;

  static this()
  {
      foo = new Foo;
  }

  static ~this()
  {
      foo.doStuff();
  }

So you see, if foo had already been destroyed and garbage collected, my program would have crashed when the module static destructor was run. Thus, I guess, running the garbage collector for the final time has to be one of the last things done on program shutdown, after running all module destructors.

-Lars

Lars T. Kyllingstad wrote:

> On Tue, 05 Oct 2010 23:25:36 +0200, vano wrote:
> 
>> The code below:
>>      module used;
>> 
>>      import std.stdio;
>> 
>>      class ClassA {
>>          this()  { writeln("A ctor"); }
>>          ~this() { writeln("A dtor"); }
>>      }
>> 
>>      static this()  { writeln("used.sctor"); } static ~this() {
>>      writeln("used.sdtor"); }
>> 
>>      void main() {
>>          auto a = new ClassA();
>>      }
>> produces the following output (DMD v2.049):
>>      used.sctor
>>      A ctor
>>      used.sdtor
>>      A dtor
>> 
>> The question is: should the module be allowed to be unloaded before all module-level objects/structures are destructed/unloaded?
> 
> 
> I'm no expert on this, but I think it has to be that way.  Consider this:
> 
>   class Foo { ... }
>   Foo foo;
> 
>   static this()
>   {
>       foo = new Foo;
>   }
> 
>   static ~this()
>   {
>       foo.doStuff();
>   }
> 
> So you see, if foo had already been destroyed and garbage collected, my program would have crashed when the module static destructor was run. Thus, I guess, running the garbage collector for the final time has to be one of the last things done on program shutdown, after running all module destructors.
> 
> -Lars

In this case however, foo is still referenced whereas in the original example 'a' is unreferenced after main exits.

I could only find this in the spec: "The garbage collector is not guaranteed to run the destructor for all unreferenced objects." *

From reading the spec, I think that all one can conclude is that after main unreferenced objects may be finalized any time, or not at all.

* http://www.digitalmars.com/d/2.0/class.html#Destructor