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c#.netgarbage-collectiongarbage

Possible to force an object to be garbage collected in Gen 1 or Gen 2 and not in Gen 0?

An interviewer asked me a weird question of which I couldn't find answer.

Is it possible to force an object to be garbage collected in Gen 1 or Gen 2 and not in Gen 0?

Solution

  • You can't... But you can extend the life of an object until some point. The simplest way inside a method is to have a:

    var myObject = new MyObject();

... some code
... some other code

// The object won't be colleted until this point **at least**
GC.KeepAlive(myObject)

    Or you can use GCHandle:

    var myObject = new MyObject();
this.Handle = GCHandle.Alloc(new object(), GCHandleType.Normal);

    (where this.Handle is a field of your object)

    and perhaps in another method:

    this.Handle.Free();

    The description of GCHandleType.Normal is:

    You can use this type to track an object and prevent its collection by the garbage collector. This enumeration member is useful when an unmanaged client holds the only reference, which is undetectable from the garbage collector, to a managed object.

    Note that if you do this (the GCHandle "this") inside a class, you should implement the IDisposable pattern to free the this.Handle.

    Ok... Technically you could:

    var myObject = new MyObject();
GC.Collect(0); // collects all gen0 objects... Uncollected gen0 objects become gen1
GC.KeepAlive(myObject);

    Now myObject is gen1... But this won't really solve your problem :-)