class gc

[Jon Olson]

On Fri, 26 Feb 1999, Godmar Back wrote:

>I don't see how any of these suggestions would work.
>The problem is not walking the class objects, the problem is marking
>class objects when following references.  These references may or may not 
>refer to objects that were allocated on the heap.  In most cases, they're not,
>and if you can help it, you don't want to check every time, or at least
>make the check as cheap as possible (cheaper than what Boehm's or Kaffe's
>gc does to find out whether an address points to an object in the heap.)
>

If you know that a reference indeed points to a class object, and all class
objects have the same format (ie. that layed out by the gcj compiler).  Just
add a bit to the `accflags' to indicate that a particular class is dynamically
allocated.  This bit would be zero for statically allocated classes generated
by the compiler, but non-zero for dynamically generated classes, like
[Ljava/lang/Object; allocated by the run-time environment.

In the case of a word which may or may not be a pointer (ie. one which is
being conservatively scanned), you'll need to do the typical conservative
heap checks anyway.

--
Jon Olson, Modular Mining Systems
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