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Thanks for the answer; I'm going to look at it in more details once I'm
back from vacation (three weeks from now)!
Kind regards,
Moritz
Rick McGuire schrieb:
> The ooRexx garbage collector is partially generational. All of the
> objects contained in the flattened rexx.img file are restored into a
> separate object space and given a special mark ("OldSpace") that
> indicates these objects are never to be garbage collected. They are
> also not traced during a garbage collection cycle, which can cause a
> problem if a reference to an object residing in the normal object heap
> is ever stored in a field of an oldspace object. Without special
> attention, these objects could end up getting garbage collected
> inappropriately.
>
> To solve this problem, the OrefSet macro is used to detect the
> situation where a new space object is being stored in an oldspace
> object. This implements a write barrier that detects that situation
> and adds the object to a special table that tracks all references from
> the oldspace to the newspace. The reference count is a counter of how
> many references we have. The OrefSet barrier also detects if the
> field being written into crosses that barrier so that the reference
> counts can be decremented.
>
> OrefSet is necessary for setting any reference field in a class that
> might get stored in the saved image. Classes that don't implement
> this properly can result in some very nasty (and hard to debug)
> garbage collection problems. Generally, it is good practice to use
> OrefSet whenever you are setting an object reference. The one
> exclusion are any of the classes in the <Transient> grouping in
> PrimitiveClasses.xml. These are classes that represent runtime state,
> and will never be stored in the image file. These classes are
> permitted to just directly assign the fields without requiring
> OrefSet(). That is the only exception, but you need to understand the
> situation when deciding not to use OrefSet(). If not certain of
> whether it is required, then use it, since it is never an error to use
> it, but it might be an error to omit it.
>
> Rick
>
> On Tue, Jun 30, 2009 at 8:38 AM, Moritz Hoffmann<antig...@gmail.com> wrote:
> Hi all,
> I have been browsing through the ooRexx source code and came to some
> point where RexxMemory::setOref() is called. I think this was from
> whithin the macro OrefSet.
>
> It would be nice if someone could explain what the method does! I see
> that it maintains some reference count. What is this used for? I though
> thought the ooRexx reference handling and object deallocation was based
> on reachability, and not on reference counting...?
>
> Thanks in advance,
> Moritz
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