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8215985: ZGC: Simplify reference processing in light of JDK-8175797

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Only self-loop 'next' field for FinalReference deactivation.

Reviewed-by: eosterlund, pliden
This commit is contained in:
Kim Barrett 2019-01-07 15:20:23 -05:00
parent fc741865bd
commit 6a3c8e4c10
2 changed files with 18 additions and 28 deletions
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41
src/hotspot/share/gc/z/zReferenceProcessor.cpp
View File

@ -1,5 +1,5 @@
/*
* Copyright (c) 2015, 2018, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2015, 2019, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@ -68,9 +68,9 @@ void ZReferenceProcessor::update_soft_reference_clock() const {
java_lang_ref_SoftReference::set_clock(now);
}
bool ZReferenceProcessor::is_reference_inactive(oop obj) const {
// A non-null next field means the reference is inactive
return java_lang_ref_Reference::next(obj) != NULL;
bool ZReferenceProcessor::is_inactive_final_reference(oop obj, ReferenceType type) const {
// A non-null next field for a FinalReference means the reference is inactive.
return (type == REF_FINAL) && (java_lang_ref_Reference::next(obj) != NULL);
}
ReferenceType ZReferenceProcessor::reference_type(oop obj) const {
@ -167,11 +167,6 @@ bool ZReferenceProcessor::should_mark_referent(ReferenceType type) const {
return type == REF_FINAL;
}
bool ZReferenceProcessor::should_clear_referent(ReferenceType type) const {
// Referents that were not marked must be cleared
return !should_mark_referent(type);
}
void ZReferenceProcessor::keep_referent_alive(oop obj, ReferenceType type) const {
volatile oop* const p = reference_referent_addr(obj);
if (type == REF_PHANTOM) {
@ -192,8 +187,8 @@ bool ZReferenceProcessor::discover_reference(oop obj, ReferenceType type) {
// Update statistics
_encountered_count.get()[type]++;
if (is_reference_inactive(obj) ||
is_referent_strongly_alive_or_null(obj, type) ||
if (is_referent_strongly_alive_or_null(obj, type) ||
is_inactive_final_reference(obj, type) ||
is_referent_softly_alive(obj, type)) {
// Not discovered
return false;
@ -242,23 +237,19 @@ oop* ZReferenceProcessor::keep(oop obj, ReferenceType type) {
// Update statistics
_enqueued_count.get()[type]++;
// Clear referent
if (should_clear_referent(type)) {
if (type != REF_FINAL) {
// Clear referent
java_lang_ref_Reference::set_referent(obj, NULL);
} else {
// For a FinalReference, don't clear the referent, because it is
// needed for the finalize call. Instead, make the reference
// inactive by self-looping the 'next' field. FinalReference
// doesn't allow Reference.enqueue, so there's no race to worry
// about when setting 'next'.
assert(java_lang_ref_Reference::next(obj) == NULL, "enqueued FinalReference");
java_lang_ref_Reference::set_next_raw(obj, obj);
}
// Make reference inactive by self-looping the next field. We could be racing with a
// call to Reference.enqueue() from the application, which is why we are using a CAS
// to make sure we change the next field only if it is NULL. A failing CAS means the
// reference has already been enqueued. However, we don't check the result of the CAS,
// since we still have no option other than keeping the reference on the pending list.
// It's ok to have the reference both on the pending list and enqueued at the same
// time (the pending list is linked through the discovered field, while the reference
// queue is linked through the next field). When the ReferenceHandler thread later
// calls Reference.enqueue() we detect that it has already been enqueued and drop it.
oop* const next_addr = (oop*)java_lang_ref_Reference::next_addr_raw(obj);
Atomic::cmpxchg(obj, next_addr, oop(NULL));
// Return next in list
return (oop*)java_lang_ref_Reference::discovered_addr_raw(obj);
}

5
src/hotspot/share/gc/z/zReferenceProcessor.hpp
View File

@ -1,5 +1,5 @@
/*
* Copyright (c) 2015, 2018, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2015, 2019, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@ -52,12 +52,11 @@ private:
const char* reference_type_name(ReferenceType type) const;
volatile oop* reference_referent_addr(oop obj) const;
oop reference_referent(oop obj) const;
bool is_reference_inactive(oop obj) const;
bool is_inactive_final_reference(oop obj, ReferenceType type) const;
bool is_referent_strongly_alive_or_null(oop obj, ReferenceType type) const;
bool is_referent_softly_alive(oop obj, ReferenceType type) const;
bool should_drop_reference(oop obj, ReferenceType type) const;
bool should_mark_referent(ReferenceType type) const;
bool should_clear_referent(ReferenceType type) const;
void keep_referent_alive(oop obj, ReferenceType type) const;
void discover(oop obj, ReferenceType type);