[plt-scheme] Re: Finalizer or custodian for extension's resources?

Matthew Flatt wrote:
>   For list-related administrative tasks:
>   http://list.cs.brown.edu/mailman/listinfo/plt-scheme
> 
> At Sun, 13 Jul 2003 20:10:56 +0200, Dirk Gerrits wrote:
> 
>>I'm a bit confused on how to tackle resources that need deallocation in 
>>MzScheme extensions. I have tried both scheme_register_finalizer on the 
>>void* itself, and scheme_add_managed on the object containing the void* 
>>but neither does exactly what I want. The former only seems to call the 
>>deallocation function on garbage collection of the resource, the latter 
>>only when the program ends. But the resource would have to be 
> 
> 
> The intent of the API is that if you want finalization in both cases,
> then you should register both ways (i.e., both the #1 and #2 lines in
> your example).

Thanks for the quick response. I just tried this, but I couldn't get it 
to work. With strong=0, the pointer can be garbage collected but the 
finalizer isn't called if it happens. With strong=1, the pointer can't 
be garbage collected because the custodian is keeping it alive.

What am I doing wrong now?

Dirk Gerrits


Here is the changed code:

void destroy_foo1(void* p, void*)
{
     Foo* foo = static_cast<Foo*>(p);
     foo->~Foo();
}
void destroy_foo2(Scheme_Object*, void* p)
{
     Foo* foo = static_cast<Foo*>(p);
     foo->~Foo();
}

Scheme_Object* create_func(int argc, Scheme_Object* argv[])
{
     void* foo = scheme_malloc_atomic(sizeof(Foo));
     new (foo) Foo;
     scheme_register_finalizer(foo, &destroy_foo1, 0, 0, 0);

     Scheme_Object* proc = scheme_make_closed_prim_w_arity(
         &func,
         foo,
         "func",
         0, 0);
     scheme_add_managed(0, proc, &destroy_foo2, foo, 0 /* 1 */);
     return proc;
};

For strong=0 I get:

DrScheme: (define func (create-func))
Log after evaluation: Foo()
Log after exit: Foo() ~Foo()

DrScheme: (create-func) (collect-garbage)
Log after evaluation: Foo()
Log after exit: Foo()

For strong=1 I get:

DrScheme: (define func (create-func))
Log after evaluation: Foo()
Log after exit: Foo() ~Foo()

DrScheme: (create-func) (collect-garbage)
Log after evaluation: Foo()
Log after exit: Foo() ~Foo()