how to mark an object for garbage collection ??

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cmrchs@yahoo.com - 27 Jun 2005 17:49 GMT

Hi,

how do you mark an object for garbage collection in C++.NET 2005 ?

MyDbClass^ obj = gcnew MyDbClass();

// Release the object
obj = 0; --> COMPILER ERROR
obj = nullptr; // nope : this does not mark it for garbage
// collection (see help)

so ... how ?

thanks
Chris

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Carl Daniel [VC++ MVP] - 27 Jun 2005 19:13 GMT

Chris C wrote:

> Hi,
>
[quoted text clipped - 8 lines]
>
> so ... how ?

You do not "mark objects for garbage collection". You simply stop
referencing them (e.g. by setting your reference to nullptr) and the GC
_MAY_ come along and collect the object at some point in the future.

If you need deterministic destruction, allocate the object "on the stack":

MyDbClass obj();

The compiler will translate this to something like:

MyDbClass^ obj=null;
try {
obj = gcnew MyDbClass();
// do stuff with object
}
finally {
if (null != obj)
obj.Dispose();
}

-cd

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Willy Denoyette [MVP] - 28 Jun 2005 17:52 GMT

Allocating an object "on the stack" will not trigger a GC either when it
goes out-of scope. Provided it has a destructor, Dispose() is automatically
called when it leaves the scope, but that's it. The object will be collected
non-deterministically when the GC comes along.

Willy.

> Chris C wrote:
>> Hi,
[quoted text clipped - 31 lines]
>
> -cd

Reply to this Message

Carl Daniel [VC++ MVP] - 29 Jun 2005 00:19 GMT

> Allocating an object "on the stack" will not trigger a GC either when
> it goes out-of scope. Provided it has a destructor, Dispose() is
> automatically called when it leaves the scope, but that's it. The
> object will be collected non-deterministically when the GC comes
> along.

I believe that's what I said. Bottom line for the OP: there is no such
thing as marking an object for collection or forcing an object to be
collected. You can force an object to be disposed, which is the technique
of preference for situations where you need deterministic cleanup of
non-memory resources (like DB connections).

-cd

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Ronald Laeremans [MSFT] - 29 Jun 2005 06:59 GMT

>>Allocating an object "on the stack" will not trigger a GC either when
>>it goes out-of scope. Provided it has a destructor, Dispose() is
[quoted text clipped - 9 lines]
>
> -cd

Also setting the reference to nullptr for a local does nothing useful
whatsoever. The JIT compiler marks GC lifetime regions, so if after a
certain point in the IL you no longer reference this object, the memory
it uses can be collected from that time on regardless of whether the
local reference still points to it.

Look here for the details:
http://blogs.msdn.com/yunjin/archive/2005/05/15/417569.aspx

Ronald Laeremans
Visual C++ team

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how to mark an object for garbage collection ??

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