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<font face="Times New Roman, Times, serif">Thanks Kim and Stefan for
the explanation.<br>
<br>
Change looks good.<br>
<br>
Jon<br>
<br>
</font><br>
<div class="moz-cite-prefix">On 12/09/2015 01:20 AM, Stefan
Johansson wrote:<br>
</div>
<blockquote cite="mid:5667F244.7040403@oracle.com" type="cite">
<br>
<br>
On 2015-12-08 22:16, Kim Barrett wrote:
<br>
<blockquote type="cite">On Dec 8, 2015, at 3:34 PM, Jon Masamitsu
<a class="moz-txt-link-rfc2396E" href="mailto:jon.masamitsu@oracle.com"><jon.masamitsu@oracle.com></a> wrote:
<br>
<blockquote type="cite">Stefan,
<br>
<br>
At line 41 in "share/vm/oops/instanceRefKlass.inline.hpp"
<br>
<br>
38 void
InstanceRefKlass::oop_oop_iterate_ref_processing_specialized(oop
obj, OopClosureType* closure,
<br>
Contains& contains) {
<br>
39 T* disc_addr =
(T*)java_lang_ref_Reference::discovered_addr(obj);
<br>
40 if
(closure->apply_to_weak_ref_discovered_field()) {
<br>
41 Devirtualizer<nv>::do_oop(closure,
disc_addr);
<br>
42 }
<br>
<br>
you're saying that the "next" field of "obj" is
<br>
non-null? Did you try adding a guarantee to that
<br>
effect and run your testing (without your change,
<br>
of course)?
<br>
</blockquote>
If next is NULL then, <em>for the specific closure in
question</em>, discovered must also be NULL here. There
is no point in applying closure to the NULL-valued discovered
field. There are other closures for which that relationship
between next and discovered doesn’t hold, but we think it will
turn out that none of them have
apply_to_weak_ref_discovered_field returning true.
<br>
<br>
Note that if next is non-NULL, then the closure will be applied
to discovered in the normal path, and there is no need for this
special case forced application (and is in fact duplicating work
at present, which could be a bug on its own, except we think the
special case is going away).
<br>
<br>
<br>
</blockquote>
As Kim say, for this specific closure the assumption holds, but
it's not true for all closures. Some time ago I did test-runs with
extra debug code to see which closures were applied with
discovered field set but next field NULL. The two closures that
showed up was:
<br>
FilterOutOfRegionClosure
<br>
G1ParPushHeapRSClosure
<br>
<br>
They both have apply_to_weak_ref_discovered_field returning true,
but to me it is not clear that they need it. My goal is to remove
all other use of apply_to_weak_ref_discovered_field first and then
attack those two. Either by somehow showing that the special case
is no longer needed or by handling the discovered field (or
actually the discovered list) some other way.
<br>
<br>
</blockquote>
<br>
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