1354 lines
51 KiB
C++
1354 lines
51 KiB
C++
/*
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* Copyright (c) 2001, 2014, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*
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*/
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#include "precompiled.hpp"
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#include "classfile/javaClasses.hpp"
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#include "classfile/systemDictionary.hpp"
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#include "gc_implementation/shared/gcTimer.hpp"
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#include "gc_implementation/shared/gcTraceTime.hpp"
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#include "gc_interface/collectedHeap.hpp"
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#include "gc_interface/collectedHeap.inline.hpp"
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#include "memory/referencePolicy.hpp"
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#include "memory/referenceProcessor.hpp"
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#include "oops/oop.inline.hpp"
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#include "runtime/java.hpp"
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#include "runtime/jniHandles.hpp"
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PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
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ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL;
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ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = NULL;
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bool ReferenceProcessor::_pending_list_uses_discovered_field = false;
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jlong ReferenceProcessor::_soft_ref_timestamp_clock = 0;
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void referenceProcessor_init() {
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ReferenceProcessor::init_statics();
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}
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void ReferenceProcessor::init_statics() {
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// We need a monotonically non-decreasing time in ms but
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// os::javaTimeMillis() does not guarantee monotonicity.
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jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
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// Initialize the soft ref timestamp clock.
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_soft_ref_timestamp_clock = now;
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// Also update the soft ref clock in j.l.r.SoftReference
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java_lang_ref_SoftReference::set_clock(_soft_ref_timestamp_clock);
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_always_clear_soft_ref_policy = new AlwaysClearPolicy();
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_default_soft_ref_policy = new COMPILER2_PRESENT(LRUMaxHeapPolicy())
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NOT_COMPILER2(LRUCurrentHeapPolicy());
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if (_always_clear_soft_ref_policy == NULL || _default_soft_ref_policy == NULL) {
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vm_exit_during_initialization("Could not allocate reference policy object");
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}
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guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery ||
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RefDiscoveryPolicy == ReferentBasedDiscovery,
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"Unrecognized RefDiscoveryPolicy");
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_pending_list_uses_discovered_field = JDK_Version::current().pending_list_uses_discovered_field();
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}
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void ReferenceProcessor::enable_discovery(bool check_no_refs) {
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#ifdef ASSERT
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// Verify that we're not currently discovering refs
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assert(!_discovering_refs, "nested call?");
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if (check_no_refs) {
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// Verify that the discovered lists are empty
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verify_no_references_recorded();
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}
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#endif // ASSERT
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// Someone could have modified the value of the static
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// field in the j.l.r.SoftReference class that holds the
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// soft reference timestamp clock using reflection or
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// Unsafe between GCs. Unconditionally update the static
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// field in ReferenceProcessor here so that we use the new
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// value during reference discovery.
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_soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
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_discovering_refs = true;
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}
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ReferenceProcessor::ReferenceProcessor(MemRegion span,
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bool mt_processing,
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uint mt_processing_degree,
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bool mt_discovery,
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uint mt_discovery_degree,
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bool atomic_discovery,
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BoolObjectClosure* is_alive_non_header) :
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_discovering_refs(false),
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_enqueuing_is_done(false),
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_is_alive_non_header(is_alive_non_header),
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_processing_is_mt(mt_processing),
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_next_id(0)
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{
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_span = span;
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_discovery_is_atomic = atomic_discovery;
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_discovery_is_mt = mt_discovery;
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_num_q = MAX2(1U, mt_processing_degree);
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_max_num_q = MAX2(_num_q, mt_discovery_degree);
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_discovered_refs = NEW_C_HEAP_ARRAY(DiscoveredList,
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_max_num_q * number_of_subclasses_of_ref(), mtGC);
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if (_discovered_refs == NULL) {
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vm_exit_during_initialization("Could not allocated RefProc Array");
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}
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_discoveredSoftRefs = &_discovered_refs[0];
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_discoveredWeakRefs = &_discoveredSoftRefs[_max_num_q];
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_discoveredFinalRefs = &_discoveredWeakRefs[_max_num_q];
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_discoveredPhantomRefs = &_discoveredFinalRefs[_max_num_q];
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// Initialize all entries to NULL
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for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
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_discovered_refs[i].set_head(NULL);
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_discovered_refs[i].set_length(0);
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}
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setup_policy(false /* default soft ref policy */);
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}
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#ifndef PRODUCT
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void ReferenceProcessor::verify_no_references_recorded() {
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guarantee(!_discovering_refs, "Discovering refs?");
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for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
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guarantee(_discovered_refs[i].is_empty(),
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"Found non-empty discovered list");
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}
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}
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#endif
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void ReferenceProcessor::weak_oops_do(OopClosure* f) {
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for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
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if (UseCompressedOops) {
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f->do_oop((narrowOop*)_discovered_refs[i].adr_head());
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} else {
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f->do_oop((oop*)_discovered_refs[i].adr_head());
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}
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}
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}
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void ReferenceProcessor::update_soft_ref_master_clock() {
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// Update (advance) the soft ref master clock field. This must be done
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// after processing the soft ref list.
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// We need a monotonically non-decreasing time in ms but
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// os::javaTimeMillis() does not guarantee monotonicity.
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jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
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jlong soft_ref_clock = java_lang_ref_SoftReference::clock();
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assert(soft_ref_clock == _soft_ref_timestamp_clock, "soft ref clocks out of sync");
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NOT_PRODUCT(
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if (now < _soft_ref_timestamp_clock) {
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warning("time warp: "INT64_FORMAT" to "INT64_FORMAT,
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_soft_ref_timestamp_clock, now);
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}
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)
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// The values of now and _soft_ref_timestamp_clock are set using
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// javaTimeNanos(), which is guaranteed to be monotonically
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// non-decreasing provided the underlying platform provides such
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// a time source (and it is bug free).
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// In product mode, however, protect ourselves from non-monotonicity.
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if (now > _soft_ref_timestamp_clock) {
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_soft_ref_timestamp_clock = now;
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java_lang_ref_SoftReference::set_clock(now);
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}
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// Else leave clock stalled at its old value until time progresses
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// past clock value.
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}
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size_t ReferenceProcessor::total_count(DiscoveredList lists[]) {
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size_t total = 0;
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for (uint i = 0; i < _max_num_q; ++i) {
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total += lists[i].length();
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}
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return total;
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}
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ReferenceProcessorStats ReferenceProcessor::process_discovered_references(
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BoolObjectClosure* is_alive,
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OopClosure* keep_alive,
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VoidClosure* complete_gc,
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AbstractRefProcTaskExecutor* task_executor,
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GCTimer* gc_timer,
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GCId gc_id) {
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NOT_PRODUCT(verify_ok_to_handle_reflists());
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assert(!enqueuing_is_done(), "If here enqueuing should not be complete");
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// Stop treating discovered references specially.
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disable_discovery();
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// If discovery was concurrent, someone could have modified
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// the value of the static field in the j.l.r.SoftReference
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// class that holds the soft reference timestamp clock using
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// reflection or Unsafe between when discovery was enabled and
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// now. Unconditionally update the static field in ReferenceProcessor
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// here so that we use the new value during processing of the
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// discovered soft refs.
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_soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
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bool trace_time = PrintGCDetails && PrintReferenceGC;
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// Soft references
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size_t soft_count = 0;
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{
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GCTraceTime tt("SoftReference", trace_time, false, gc_timer, gc_id);
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soft_count =
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process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true,
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is_alive, keep_alive, complete_gc, task_executor);
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}
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update_soft_ref_master_clock();
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// Weak references
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size_t weak_count = 0;
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{
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GCTraceTime tt("WeakReference", trace_time, false, gc_timer, gc_id);
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weak_count =
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process_discovered_reflist(_discoveredWeakRefs, NULL, true,
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is_alive, keep_alive, complete_gc, task_executor);
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}
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// Final references
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size_t final_count = 0;
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{
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GCTraceTime tt("FinalReference", trace_time, false, gc_timer, gc_id);
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final_count =
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process_discovered_reflist(_discoveredFinalRefs, NULL, false,
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is_alive, keep_alive, complete_gc, task_executor);
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}
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// Phantom references
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size_t phantom_count = 0;
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{
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GCTraceTime tt("PhantomReference", trace_time, false, gc_timer, gc_id);
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phantom_count =
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process_discovered_reflist(_discoveredPhantomRefs, NULL, false,
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is_alive, keep_alive, complete_gc, task_executor);
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}
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// Weak global JNI references. It would make more sense (semantically) to
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// traverse these simultaneously with the regular weak references above, but
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// that is not how the JDK1.2 specification is. See #4126360. Native code can
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// thus use JNI weak references to circumvent the phantom references and
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// resurrect a "post-mortem" object.
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{
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GCTraceTime tt("JNI Weak Reference", trace_time, false, gc_timer, gc_id);
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if (task_executor != NULL) {
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task_executor->set_single_threaded_mode();
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}
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process_phaseJNI(is_alive, keep_alive, complete_gc);
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}
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return ReferenceProcessorStats(soft_count, weak_count, final_count, phantom_count);
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}
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#ifndef PRODUCT
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// Calculate the number of jni handles.
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uint ReferenceProcessor::count_jni_refs() {
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class AlwaysAliveClosure: public BoolObjectClosure {
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public:
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virtual bool do_object_b(oop obj) { return true; }
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};
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class CountHandleClosure: public OopClosure {
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private:
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int _count;
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public:
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CountHandleClosure(): _count(0) {}
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void do_oop(oop* unused) { _count++; }
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void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
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int count() { return _count; }
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};
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CountHandleClosure global_handle_count;
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AlwaysAliveClosure always_alive;
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JNIHandles::weak_oops_do(&always_alive, &global_handle_count);
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return global_handle_count.count();
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}
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#endif
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void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive,
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OopClosure* keep_alive,
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VoidClosure* complete_gc) {
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#ifndef PRODUCT
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if (PrintGCDetails && PrintReferenceGC) {
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unsigned int count = count_jni_refs();
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gclog_or_tty->print(", %u refs", count);
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}
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#endif
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JNIHandles::weak_oops_do(is_alive, keep_alive);
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complete_gc->do_void();
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}
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template <class T>
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bool enqueue_discovered_ref_helper(ReferenceProcessor* ref,
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AbstractRefProcTaskExecutor* task_executor) {
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// Remember old value of pending references list
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T* pending_list_addr = (T*)java_lang_ref_Reference::pending_list_addr();
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T old_pending_list_value = *pending_list_addr;
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// Enqueue references that are not made active again, and
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// clear the decks for the next collection (cycle).
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ref->enqueue_discovered_reflists((HeapWord*)pending_list_addr, task_executor);
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// Do the post-barrier on pending_list_addr missed in
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// enqueue_discovered_reflist.
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oopDesc::bs()->write_ref_field(pending_list_addr, oopDesc::load_decode_heap_oop(pending_list_addr));
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// Stop treating discovered references specially.
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ref->disable_discovery();
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// Return true if new pending references were added
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return old_pending_list_value != *pending_list_addr;
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}
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bool ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor) {
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NOT_PRODUCT(verify_ok_to_handle_reflists());
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if (UseCompressedOops) {
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return enqueue_discovered_ref_helper<narrowOop>(this, task_executor);
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} else {
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return enqueue_discovered_ref_helper<oop>(this, task_executor);
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}
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}
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void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list,
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HeapWord* pending_list_addr) {
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// Given a list of refs linked through the "discovered" field
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// (java.lang.ref.Reference.discovered), self-loop their "next" field
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// thus distinguishing them from active References, then
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// prepend them to the pending list.
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//
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// The Java threads will see the Reference objects linked together through
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// the discovered field. Instead of trying to do the write barrier updates
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// in all places in the reference processor where we manipulate the discovered
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// field we make sure to do the barrier here where we anyway iterate through
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// all linked Reference objects. Note that it is important to not dirty any
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// cards during reference processing since this will cause card table
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// verification to fail for G1.
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//
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// BKWRD COMPATIBILITY NOTE: For older JDKs (prior to the fix for 4956777),
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// the "next" field is used to chain the pending list, not the discovered
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// field.
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if (TraceReferenceGC && PrintGCDetails) {
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gclog_or_tty->print_cr("ReferenceProcessor::enqueue_discovered_reflist list "
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INTPTR_FORMAT, (address)refs_list.head());
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}
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oop obj = NULL;
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oop next_d = refs_list.head();
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if (pending_list_uses_discovered_field()) { // New behavior
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// Walk down the list, self-looping the next field
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// so that the References are not considered active.
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while (obj != next_d) {
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obj = next_d;
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assert(obj->is_instanceRef(), "should be reference object");
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next_d = java_lang_ref_Reference::discovered(obj);
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if (TraceReferenceGC && PrintGCDetails) {
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gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT,
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(void *)obj, (void *)next_d);
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}
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assert(java_lang_ref_Reference::next(obj) == NULL,
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"Reference not active; should not be discovered");
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// Self-loop next, so as to make Ref not active.
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java_lang_ref_Reference::set_next_raw(obj, obj);
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if (next_d != obj) {
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oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), next_d);
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} else {
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// This is the last object.
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// Swap refs_list into pending_list_addr and
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// set obj's discovered to what we read from pending_list_addr.
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oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr);
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// Need post-barrier on pending_list_addr. See enqueue_discovered_ref_helper() above.
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java_lang_ref_Reference::set_discovered_raw(obj, old); // old may be NULL
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oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), old);
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}
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}
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} else { // Old behavior
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// Walk down the list, copying the discovered field into
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// the next field and clearing the discovered field.
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while (obj != next_d) {
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obj = next_d;
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assert(obj->is_instanceRef(), "should be reference object");
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next_d = java_lang_ref_Reference::discovered(obj);
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if (TraceReferenceGC && PrintGCDetails) {
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gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT,
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(void *)obj, (void *)next_d);
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}
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assert(java_lang_ref_Reference::next(obj) == NULL,
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"The reference should not be enqueued");
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if (next_d == obj) { // obj is last
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// Swap refs_list into pending_list_addr and
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// set obj's next to what we read from pending_list_addr.
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oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr);
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// Need oop_check on pending_list_addr above;
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// see special oop-check code at the end of
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// enqueue_discovered_reflists() further below.
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if (old == NULL) {
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// obj should be made to point to itself, since
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// pending list was empty.
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java_lang_ref_Reference::set_next(obj, obj);
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} else {
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java_lang_ref_Reference::set_next(obj, old);
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}
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} else {
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java_lang_ref_Reference::set_next(obj, next_d);
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}
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java_lang_ref_Reference::set_discovered(obj, (oop) NULL);
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}
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}
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}
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// Parallel enqueue task
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class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask {
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public:
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RefProcEnqueueTask(ReferenceProcessor& ref_processor,
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DiscoveredList discovered_refs[],
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HeapWord* pending_list_addr,
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int n_queues)
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: EnqueueTask(ref_processor, discovered_refs,
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pending_list_addr, n_queues)
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{ }
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virtual void work(unsigned int work_id) {
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assert(work_id < (unsigned int)_ref_processor.max_num_q(), "Index out-of-bounds");
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// Simplest first cut: static partitioning.
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int index = work_id;
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// The increment on "index" must correspond to the maximum number of queues
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// (n_queues) with which that ReferenceProcessor was created. That
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// is because of the "clever" way the discovered references lists were
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// allocated and are indexed into.
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assert(_n_queues == (int) _ref_processor.max_num_q(), "Different number not expected");
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for (int j = 0;
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j < ReferenceProcessor::number_of_subclasses_of_ref();
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j++, index += _n_queues) {
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_ref_processor.enqueue_discovered_reflist(
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_refs_lists[index], _pending_list_addr);
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_refs_lists[index].set_head(NULL);
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_refs_lists[index].set_length(0);
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}
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}
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};
|
|
|
|
// Enqueue references that are not made active again
|
|
void ReferenceProcessor::enqueue_discovered_reflists(HeapWord* pending_list_addr,
|
|
AbstractRefProcTaskExecutor* task_executor) {
|
|
if (_processing_is_mt && task_executor != NULL) {
|
|
// Parallel code
|
|
RefProcEnqueueTask tsk(*this, _discovered_refs,
|
|
pending_list_addr, _max_num_q);
|
|
task_executor->execute(tsk);
|
|
} else {
|
|
// Serial code: call the parent class's implementation
|
|
for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
|
|
enqueue_discovered_reflist(_discovered_refs[i], pending_list_addr);
|
|
_discovered_refs[i].set_head(NULL);
|
|
_discovered_refs[i].set_length(0);
|
|
}
|
|
}
|
|
}
|
|
|
|
void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) {
|
|
_discovered_addr = java_lang_ref_Reference::discovered_addr(_ref);
|
|
oop discovered = java_lang_ref_Reference::discovered(_ref);
|
|
assert(_discovered_addr && discovered->is_oop_or_null(),
|
|
err_msg("Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered)));
|
|
_next = discovered;
|
|
_referent_addr = java_lang_ref_Reference::referent_addr(_ref);
|
|
_referent = java_lang_ref_Reference::referent(_ref);
|
|
assert(Universe::heap()->is_in_reserved_or_null(_referent),
|
|
"Wrong oop found in java.lang.Reference object");
|
|
assert(allow_null_referent ?
|
|
_referent->is_oop_or_null()
|
|
: _referent->is_oop(),
|
|
err_msg("Expected an oop%s for referent field at " PTR_FORMAT,
|
|
(allow_null_referent ? " or NULL" : ""),
|
|
p2i(_referent)));
|
|
}
|
|
|
|
void DiscoveredListIterator::remove() {
|
|
assert(_ref->is_oop(), "Dropping a bad reference");
|
|
oop_store_raw(_discovered_addr, NULL);
|
|
|
|
// First _prev_next ref actually points into DiscoveredList (gross).
|
|
oop new_next;
|
|
if (_next == _ref) {
|
|
// At the end of the list, we should make _prev point to itself.
|
|
// If _ref is the first ref, then _prev_next will be in the DiscoveredList,
|
|
// and _prev will be NULL.
|
|
new_next = _prev;
|
|
} else {
|
|
new_next = _next;
|
|
}
|
|
// Remove Reference object from discovered list. Note that G1 does not need a
|
|
// pre-barrier here because we know the Reference has already been found/marked,
|
|
// that's how it ended up in the discovered list in the first place.
|
|
oop_store_raw(_prev_next, new_next);
|
|
NOT_PRODUCT(_removed++);
|
|
_refs_list.dec_length(1);
|
|
}
|
|
|
|
// Make the Reference object active again.
|
|
void DiscoveredListIterator::make_active() {
|
|
// The pre barrier for G1 is probably just needed for the old
|
|
// reference processing behavior. Should we guard this with
|
|
// ReferenceProcessor::pending_list_uses_discovered_field() ?
|
|
if (UseG1GC) {
|
|
HeapWord* next_addr = java_lang_ref_Reference::next_addr(_ref);
|
|
if (UseCompressedOops) {
|
|
oopDesc::bs()->write_ref_field_pre((narrowOop*)next_addr, NULL);
|
|
} else {
|
|
oopDesc::bs()->write_ref_field_pre((oop*)next_addr, NULL);
|
|
}
|
|
}
|
|
java_lang_ref_Reference::set_next_raw(_ref, NULL);
|
|
}
|
|
|
|
void DiscoveredListIterator::clear_referent() {
|
|
oop_store_raw(_referent_addr, NULL);
|
|
}
|
|
|
|
// NOTE: process_phase*() are largely similar, and at a high level
|
|
// merely iterate over the extant list applying a predicate to
|
|
// each of its elements and possibly removing that element from the
|
|
// list and applying some further closures to that element.
|
|
// We should consider the possibility of replacing these
|
|
// process_phase*() methods by abstracting them into
|
|
// a single general iterator invocation that receives appropriate
|
|
// closures that accomplish this work.
|
|
|
|
// (SoftReferences only) Traverse the list and remove any SoftReferences whose
|
|
// referents are not alive, but that should be kept alive for policy reasons.
|
|
// Keep alive the transitive closure of all such referents.
|
|
void
|
|
ReferenceProcessor::process_phase1(DiscoveredList& refs_list,
|
|
ReferencePolicy* policy,
|
|
BoolObjectClosure* is_alive,
|
|
OopClosure* keep_alive,
|
|
VoidClosure* complete_gc) {
|
|
assert(policy != NULL, "Must have a non-NULL policy");
|
|
DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
|
|
// Decide which softly reachable refs should be kept alive.
|
|
while (iter.has_next()) {
|
|
iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */));
|
|
bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive();
|
|
if (referent_is_dead &&
|
|
!policy->should_clear_reference(iter.obj(), _soft_ref_timestamp_clock)) {
|
|
if (TraceReferenceGC) {
|
|
gclog_or_tty->print_cr("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy",
|
|
(void *)iter.obj(), iter.obj()->klass()->internal_name());
|
|
}
|
|
// Remove Reference object from list
|
|
iter.remove();
|
|
// Make the Reference object active again
|
|
iter.make_active();
|
|
// keep the referent around
|
|
iter.make_referent_alive();
|
|
iter.move_to_next();
|
|
} else {
|
|
iter.next();
|
|
}
|
|
}
|
|
// Close the reachable set
|
|
complete_gc->do_void();
|
|
NOT_PRODUCT(
|
|
if (PrintGCDetails && TraceReferenceGC) {
|
|
gclog_or_tty->print_cr(" Dropped %d dead Refs out of %d "
|
|
"discovered Refs by policy, from list " INTPTR_FORMAT,
|
|
iter.removed(), iter.processed(), (address)refs_list.head());
|
|
}
|
|
)
|
|
}
|
|
|
|
// Traverse the list and remove any Refs that are not active, or
|
|
// whose referents are either alive or NULL.
|
|
void
|
|
ReferenceProcessor::pp2_work(DiscoveredList& refs_list,
|
|
BoolObjectClosure* is_alive,
|
|
OopClosure* keep_alive) {
|
|
assert(discovery_is_atomic(), "Error");
|
|
DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
|
|
while (iter.has_next()) {
|
|
iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
|
|
DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());)
|
|
assert(next == NULL, "Should not discover inactive Reference");
|
|
if (iter.is_referent_alive()) {
|
|
if (TraceReferenceGC) {
|
|
gclog_or_tty->print_cr("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)",
|
|
(void *)iter.obj(), iter.obj()->klass()->internal_name());
|
|
}
|
|
// The referent is reachable after all.
|
|
// Remove Reference object from list.
|
|
iter.remove();
|
|
// Update the referent pointer as necessary: Note that this
|
|
// should not entail any recursive marking because the
|
|
// referent must already have been traversed.
|
|
iter.make_referent_alive();
|
|
iter.move_to_next();
|
|
} else {
|
|
iter.next();
|
|
}
|
|
}
|
|
NOT_PRODUCT(
|
|
if (PrintGCDetails && TraceReferenceGC && (iter.processed() > 0)) {
|
|
gclog_or_tty->print_cr(" Dropped %d active Refs out of %d "
|
|
"Refs in discovered list " INTPTR_FORMAT,
|
|
iter.removed(), iter.processed(), (address)refs_list.head());
|
|
}
|
|
)
|
|
}
|
|
|
|
void
|
|
ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList& refs_list,
|
|
BoolObjectClosure* is_alive,
|
|
OopClosure* keep_alive,
|
|
VoidClosure* complete_gc) {
|
|
assert(!discovery_is_atomic(), "Error");
|
|
DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
|
|
while (iter.has_next()) {
|
|
iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
|
|
HeapWord* next_addr = java_lang_ref_Reference::next_addr(iter.obj());
|
|
oop next = java_lang_ref_Reference::next(iter.obj());
|
|
if ((iter.referent() == NULL || iter.is_referent_alive() ||
|
|
next != NULL)) {
|
|
assert(next->is_oop_or_null(), err_msg("Expected an oop or NULL for next field at " PTR_FORMAT, p2i(next)));
|
|
// Remove Reference object from list
|
|
iter.remove();
|
|
// Trace the cohorts
|
|
iter.make_referent_alive();
|
|
if (UseCompressedOops) {
|
|
keep_alive->do_oop((narrowOop*)next_addr);
|
|
} else {
|
|
keep_alive->do_oop((oop*)next_addr);
|
|
}
|
|
iter.move_to_next();
|
|
} else {
|
|
iter.next();
|
|
}
|
|
}
|
|
// Now close the newly reachable set
|
|
complete_gc->do_void();
|
|
NOT_PRODUCT(
|
|
if (PrintGCDetails && TraceReferenceGC && (iter.processed() > 0)) {
|
|
gclog_or_tty->print_cr(" Dropped %d active Refs out of %d "
|
|
"Refs in discovered list " INTPTR_FORMAT,
|
|
iter.removed(), iter.processed(), (address)refs_list.head());
|
|
}
|
|
)
|
|
}
|
|
|
|
// Traverse the list and process the referents, by either
|
|
// clearing them or keeping them (and their reachable
|
|
// closure) alive.
|
|
void
|
|
ReferenceProcessor::process_phase3(DiscoveredList& refs_list,
|
|
bool clear_referent,
|
|
BoolObjectClosure* is_alive,
|
|
OopClosure* keep_alive,
|
|
VoidClosure* complete_gc) {
|
|
ResourceMark rm;
|
|
DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
|
|
while (iter.has_next()) {
|
|
iter.update_discovered();
|
|
iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
|
|
if (clear_referent) {
|
|
// NULL out referent pointer
|
|
iter.clear_referent();
|
|
} else {
|
|
// keep the referent around
|
|
iter.make_referent_alive();
|
|
}
|
|
if (TraceReferenceGC) {
|
|
gclog_or_tty->print_cr("Adding %sreference (" INTPTR_FORMAT ": %s) as pending",
|
|
clear_referent ? "cleared " : "",
|
|
(void *)iter.obj(), iter.obj()->klass()->internal_name());
|
|
}
|
|
assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference");
|
|
iter.next();
|
|
}
|
|
// Remember to update the next pointer of the last ref.
|
|
iter.update_discovered();
|
|
// Close the reachable set
|
|
complete_gc->do_void();
|
|
}
|
|
|
|
void
|
|
ReferenceProcessor::clear_discovered_references(DiscoveredList& refs_list) {
|
|
oop obj = NULL;
|
|
oop next = refs_list.head();
|
|
while (next != obj) {
|
|
obj = next;
|
|
next = java_lang_ref_Reference::discovered(obj);
|
|
java_lang_ref_Reference::set_discovered_raw(obj, NULL);
|
|
}
|
|
refs_list.set_head(NULL);
|
|
refs_list.set_length(0);
|
|
}
|
|
|
|
void
|
|
ReferenceProcessor::abandon_partial_discovered_list(DiscoveredList& refs_list) {
|
|
clear_discovered_references(refs_list);
|
|
}
|
|
|
|
void ReferenceProcessor::abandon_partial_discovery() {
|
|
// loop over the lists
|
|
for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
|
|
if (TraceReferenceGC && PrintGCDetails && ((i % _max_num_q) == 0)) {
|
|
gclog_or_tty->print_cr("\nAbandoning %s discovered list", list_name(i));
|
|
}
|
|
abandon_partial_discovered_list(_discovered_refs[i]);
|
|
}
|
|
}
|
|
|
|
class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask {
|
|
public:
|
|
RefProcPhase1Task(ReferenceProcessor& ref_processor,
|
|
DiscoveredList refs_lists[],
|
|
ReferencePolicy* policy,
|
|
bool marks_oops_alive)
|
|
: ProcessTask(ref_processor, refs_lists, marks_oops_alive),
|
|
_policy(policy)
|
|
{ }
|
|
virtual void work(unsigned int i, BoolObjectClosure& is_alive,
|
|
OopClosure& keep_alive,
|
|
VoidClosure& complete_gc)
|
|
{
|
|
Thread* thr = Thread::current();
|
|
int refs_list_index = ((WorkerThread*)thr)->id();
|
|
_ref_processor.process_phase1(_refs_lists[refs_list_index], _policy,
|
|
&is_alive, &keep_alive, &complete_gc);
|
|
}
|
|
private:
|
|
ReferencePolicy* _policy;
|
|
};
|
|
|
|
class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask {
|
|
public:
|
|
RefProcPhase2Task(ReferenceProcessor& ref_processor,
|
|
DiscoveredList refs_lists[],
|
|
bool marks_oops_alive)
|
|
: ProcessTask(ref_processor, refs_lists, marks_oops_alive)
|
|
{ }
|
|
virtual void work(unsigned int i, BoolObjectClosure& is_alive,
|
|
OopClosure& keep_alive,
|
|
VoidClosure& complete_gc)
|
|
{
|
|
_ref_processor.process_phase2(_refs_lists[i],
|
|
&is_alive, &keep_alive, &complete_gc);
|
|
}
|
|
};
|
|
|
|
class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask {
|
|
public:
|
|
RefProcPhase3Task(ReferenceProcessor& ref_processor,
|
|
DiscoveredList refs_lists[],
|
|
bool clear_referent,
|
|
bool marks_oops_alive)
|
|
: ProcessTask(ref_processor, refs_lists, marks_oops_alive),
|
|
_clear_referent(clear_referent)
|
|
{ }
|
|
virtual void work(unsigned int i, BoolObjectClosure& is_alive,
|
|
OopClosure& keep_alive,
|
|
VoidClosure& complete_gc)
|
|
{
|
|
// Don't use "refs_list_index" calculated in this way because
|
|
// balance_queues() has moved the Ref's into the first n queues.
|
|
// Thread* thr = Thread::current();
|
|
// int refs_list_index = ((WorkerThread*)thr)->id();
|
|
// _ref_processor.process_phase3(_refs_lists[refs_list_index], _clear_referent,
|
|
_ref_processor.process_phase3(_refs_lists[i], _clear_referent,
|
|
&is_alive, &keep_alive, &complete_gc);
|
|
}
|
|
private:
|
|
bool _clear_referent;
|
|
};
|
|
|
|
// Balances reference queues.
|
|
// Move entries from all queues[0, 1, ..., _max_num_q-1] to
|
|
// queues[0, 1, ..., _num_q-1] because only the first _num_q
|
|
// corresponding to the active workers will be processed.
|
|
void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[])
|
|
{
|
|
// calculate total length
|
|
size_t total_refs = 0;
|
|
if (TraceReferenceGC && PrintGCDetails) {
|
|
gclog_or_tty->print_cr("\nBalance ref_lists ");
|
|
}
|
|
|
|
for (uint i = 0; i < _max_num_q; ++i) {
|
|
total_refs += ref_lists[i].length();
|
|
if (TraceReferenceGC && PrintGCDetails) {
|
|
gclog_or_tty->print("%d ", ref_lists[i].length());
|
|
}
|
|
}
|
|
if (TraceReferenceGC && PrintGCDetails) {
|
|
gclog_or_tty->print_cr(" = %d", total_refs);
|
|
}
|
|
size_t avg_refs = total_refs / _num_q + 1;
|
|
uint to_idx = 0;
|
|
for (uint from_idx = 0; from_idx < _max_num_q; from_idx++) {
|
|
bool move_all = false;
|
|
if (from_idx >= _num_q) {
|
|
move_all = ref_lists[from_idx].length() > 0;
|
|
}
|
|
while ((ref_lists[from_idx].length() > avg_refs) ||
|
|
move_all) {
|
|
assert(to_idx < _num_q, "Sanity Check!");
|
|
if (ref_lists[to_idx].length() < avg_refs) {
|
|
// move superfluous refs
|
|
size_t refs_to_move;
|
|
// Move all the Ref's if the from queue will not be processed.
|
|
if (move_all) {
|
|
refs_to_move = MIN2(ref_lists[from_idx].length(),
|
|
avg_refs - ref_lists[to_idx].length());
|
|
} else {
|
|
refs_to_move = MIN2(ref_lists[from_idx].length() - avg_refs,
|
|
avg_refs - ref_lists[to_idx].length());
|
|
}
|
|
|
|
assert(refs_to_move > 0, "otherwise the code below will fail");
|
|
|
|
oop move_head = ref_lists[from_idx].head();
|
|
oop move_tail = move_head;
|
|
oop new_head = move_head;
|
|
// find an element to split the list on
|
|
for (size_t j = 0; j < refs_to_move; ++j) {
|
|
move_tail = new_head;
|
|
new_head = java_lang_ref_Reference::discovered(new_head);
|
|
}
|
|
|
|
// Add the chain to the to list.
|
|
if (ref_lists[to_idx].head() == NULL) {
|
|
// to list is empty. Make a loop at the end.
|
|
java_lang_ref_Reference::set_discovered_raw(move_tail, move_tail);
|
|
} else {
|
|
java_lang_ref_Reference::set_discovered_raw(move_tail, ref_lists[to_idx].head());
|
|
}
|
|
ref_lists[to_idx].set_head(move_head);
|
|
ref_lists[to_idx].inc_length(refs_to_move);
|
|
|
|
// Remove the chain from the from list.
|
|
if (move_tail == new_head) {
|
|
// We found the end of the from list.
|
|
ref_lists[from_idx].set_head(NULL);
|
|
} else {
|
|
ref_lists[from_idx].set_head(new_head);
|
|
}
|
|
ref_lists[from_idx].dec_length(refs_to_move);
|
|
if (ref_lists[from_idx].length() == 0) {
|
|
break;
|
|
}
|
|
} else {
|
|
to_idx = (to_idx + 1) % _num_q;
|
|
}
|
|
}
|
|
}
|
|
#ifdef ASSERT
|
|
size_t balanced_total_refs = 0;
|
|
for (uint i = 0; i < _max_num_q; ++i) {
|
|
balanced_total_refs += ref_lists[i].length();
|
|
if (TraceReferenceGC && PrintGCDetails) {
|
|
gclog_or_tty->print("%d ", ref_lists[i].length());
|
|
}
|
|
}
|
|
if (TraceReferenceGC && PrintGCDetails) {
|
|
gclog_or_tty->print_cr(" = %d", balanced_total_refs);
|
|
gclog_or_tty->flush();
|
|
}
|
|
assert(total_refs == balanced_total_refs, "Balancing was incomplete");
|
|
#endif
|
|
}
|
|
|
|
void ReferenceProcessor::balance_all_queues() {
|
|
balance_queues(_discoveredSoftRefs);
|
|
balance_queues(_discoveredWeakRefs);
|
|
balance_queues(_discoveredFinalRefs);
|
|
balance_queues(_discoveredPhantomRefs);
|
|
}
|
|
|
|
size_t
|
|
ReferenceProcessor::process_discovered_reflist(
|
|
DiscoveredList refs_lists[],
|
|
ReferencePolicy* policy,
|
|
bool clear_referent,
|
|
BoolObjectClosure* is_alive,
|
|
OopClosure* keep_alive,
|
|
VoidClosure* complete_gc,
|
|
AbstractRefProcTaskExecutor* task_executor)
|
|
{
|
|
bool mt_processing = task_executor != NULL && _processing_is_mt;
|
|
// If discovery used MT and a dynamic number of GC threads, then
|
|
// the queues must be balanced for correctness if fewer than the
|
|
// maximum number of queues were used. The number of queue used
|
|
// during discovery may be different than the number to be used
|
|
// for processing so don't depend of _num_q < _max_num_q as part
|
|
// of the test.
|
|
bool must_balance = _discovery_is_mt;
|
|
|
|
if ((mt_processing && ParallelRefProcBalancingEnabled) ||
|
|
must_balance) {
|
|
balance_queues(refs_lists);
|
|
}
|
|
|
|
size_t total_list_count = total_count(refs_lists);
|
|
|
|
if (PrintReferenceGC && PrintGCDetails) {
|
|
gclog_or_tty->print(", %u refs", total_list_count);
|
|
}
|
|
|
|
// Phase 1 (soft refs only):
|
|
// . Traverse the list and remove any SoftReferences whose
|
|
// referents are not alive, but that should be kept alive for
|
|
// policy reasons. Keep alive the transitive closure of all
|
|
// such referents.
|
|
if (policy != NULL) {
|
|
if (mt_processing) {
|
|
RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/);
|
|
task_executor->execute(phase1);
|
|
} else {
|
|
for (uint i = 0; i < _max_num_q; i++) {
|
|
process_phase1(refs_lists[i], policy,
|
|
is_alive, keep_alive, complete_gc);
|
|
}
|
|
}
|
|
} else { // policy == NULL
|
|
assert(refs_lists != _discoveredSoftRefs,
|
|
"Policy must be specified for soft references.");
|
|
}
|
|
|
|
// Phase 2:
|
|
// . Traverse the list and remove any refs whose referents are alive.
|
|
if (mt_processing) {
|
|
RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/);
|
|
task_executor->execute(phase2);
|
|
} else {
|
|
for (uint i = 0; i < _max_num_q; i++) {
|
|
process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc);
|
|
}
|
|
}
|
|
|
|
// Phase 3:
|
|
// . Traverse the list and process referents as appropriate.
|
|
if (mt_processing) {
|
|
RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/);
|
|
task_executor->execute(phase3);
|
|
} else {
|
|
for (uint i = 0; i < _max_num_q; i++) {
|
|
process_phase3(refs_lists[i], clear_referent,
|
|
is_alive, keep_alive, complete_gc);
|
|
}
|
|
}
|
|
|
|
return total_list_count;
|
|
}
|
|
|
|
inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) {
|
|
uint id = 0;
|
|
// Determine the queue index to use for this object.
|
|
if (_discovery_is_mt) {
|
|
// During a multi-threaded discovery phase,
|
|
// each thread saves to its "own" list.
|
|
Thread* thr = Thread::current();
|
|
id = thr->as_Worker_thread()->id();
|
|
} else {
|
|
// single-threaded discovery, we save in round-robin
|
|
// fashion to each of the lists.
|
|
if (_processing_is_mt) {
|
|
id = next_id();
|
|
}
|
|
}
|
|
assert(0 <= id && id < _max_num_q, "Id is out-of-bounds (call Freud?)");
|
|
|
|
// Get the discovered queue to which we will add
|
|
DiscoveredList* list = NULL;
|
|
switch (rt) {
|
|
case REF_OTHER:
|
|
// Unknown reference type, no special treatment
|
|
break;
|
|
case REF_SOFT:
|
|
list = &_discoveredSoftRefs[id];
|
|
break;
|
|
case REF_WEAK:
|
|
list = &_discoveredWeakRefs[id];
|
|
break;
|
|
case REF_FINAL:
|
|
list = &_discoveredFinalRefs[id];
|
|
break;
|
|
case REF_PHANTOM:
|
|
list = &_discoveredPhantomRefs[id];
|
|
break;
|
|
case REF_NONE:
|
|
// we should not reach here if we are an InstanceRefKlass
|
|
default:
|
|
ShouldNotReachHere();
|
|
}
|
|
if (TraceReferenceGC && PrintGCDetails) {
|
|
gclog_or_tty->print_cr("Thread %d gets list " INTPTR_FORMAT, id, list);
|
|
}
|
|
return list;
|
|
}
|
|
|
|
inline void
|
|
ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list,
|
|
oop obj,
|
|
HeapWord* discovered_addr) {
|
|
assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller");
|
|
// First we must make sure this object is only enqueued once. CAS in a non null
|
|
// discovered_addr.
|
|
oop current_head = refs_list.head();
|
|
// The last ref must have its discovered field pointing to itself.
|
|
oop next_discovered = (current_head != NULL) ? current_head : obj;
|
|
|
|
oop retest = oopDesc::atomic_compare_exchange_oop(next_discovered, discovered_addr,
|
|
NULL);
|
|
if (retest == NULL) {
|
|
// This thread just won the right to enqueue the object.
|
|
// We have separate lists for enqueueing, so no synchronization
|
|
// is necessary.
|
|
refs_list.set_head(obj);
|
|
refs_list.inc_length(1);
|
|
|
|
if (TraceReferenceGC) {
|
|
gclog_or_tty->print_cr("Discovered reference (mt) (" INTPTR_FORMAT ": %s)",
|
|
(void *)obj, obj->klass()->internal_name());
|
|
}
|
|
} else {
|
|
// If retest was non NULL, another thread beat us to it:
|
|
// The reference has already been discovered...
|
|
if (TraceReferenceGC) {
|
|
gclog_or_tty->print_cr("Already discovered reference (" INTPTR_FORMAT ": %s)",
|
|
(void *)obj, obj->klass()->internal_name());
|
|
}
|
|
}
|
|
}
|
|
|
|
#ifndef PRODUCT
|
|
// Non-atomic (i.e. concurrent) discovery might allow us
|
|
// to observe j.l.References with NULL referents, being those
|
|
// cleared concurrently by mutators during (or after) discovery.
|
|
void ReferenceProcessor::verify_referent(oop obj) {
|
|
bool da = discovery_is_atomic();
|
|
oop referent = java_lang_ref_Reference::referent(obj);
|
|
assert(da ? referent->is_oop() : referent->is_oop_or_null(),
|
|
err_msg("Bad referent " INTPTR_FORMAT " found in Reference "
|
|
INTPTR_FORMAT " during %satomic discovery ",
|
|
(void *)referent, (void *)obj, da ? "" : "non-"));
|
|
}
|
|
#endif
|
|
|
|
// We mention two of several possible choices here:
|
|
// #0: if the reference object is not in the "originating generation"
|
|
// (or part of the heap being collected, indicated by our "span"
|
|
// we don't treat it specially (i.e. we scan it as we would
|
|
// a normal oop, treating its references as strong references).
|
|
// This means that references can't be discovered unless their
|
|
// referent is also in the same span. This is the simplest,
|
|
// most "local" and most conservative approach, albeit one
|
|
// that may cause weak references to be enqueued least promptly.
|
|
// We call this choice the "ReferenceBasedDiscovery" policy.
|
|
// #1: the reference object may be in any generation (span), but if
|
|
// the referent is in the generation (span) being currently collected
|
|
// then we can discover the reference object, provided
|
|
// the object has not already been discovered by
|
|
// a different concurrently running collector (as may be the
|
|
// case, for instance, if the reference object is in CMS and
|
|
// the referent in DefNewGeneration), and provided the processing
|
|
// of this reference object by the current collector will
|
|
// appear atomic to every other collector in the system.
|
|
// (Thus, for instance, a concurrent collector may not
|
|
// discover references in other generations even if the
|
|
// referent is in its own generation). This policy may,
|
|
// in certain cases, enqueue references somewhat sooner than
|
|
// might Policy #0 above, but at marginally increased cost
|
|
// and complexity in processing these references.
|
|
// We call this choice the "RefeferentBasedDiscovery" policy.
|
|
bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) {
|
|
// Make sure we are discovering refs (rather than processing discovered refs).
|
|
if (!_discovering_refs || !RegisterReferences) {
|
|
return false;
|
|
}
|
|
// We only discover active references.
|
|
oop next = java_lang_ref_Reference::next(obj);
|
|
if (next != NULL) { // Ref is no longer active
|
|
return false;
|
|
}
|
|
|
|
HeapWord* obj_addr = (HeapWord*)obj;
|
|
if (RefDiscoveryPolicy == ReferenceBasedDiscovery &&
|
|
!_span.contains(obj_addr)) {
|
|
// Reference is not in the originating generation;
|
|
// don't treat it specially (i.e. we want to scan it as a normal
|
|
// object with strong references).
|
|
return false;
|
|
}
|
|
|
|
// We only discover references whose referents are not (yet)
|
|
// known to be strongly reachable.
|
|
if (is_alive_non_header() != NULL) {
|
|
verify_referent(obj);
|
|
if (is_alive_non_header()->do_object_b(java_lang_ref_Reference::referent(obj))) {
|
|
return false; // referent is reachable
|
|
}
|
|
}
|
|
if (rt == REF_SOFT) {
|
|
// For soft refs we can decide now if these are not
|
|
// current candidates for clearing, in which case we
|
|
// can mark through them now, rather than delaying that
|
|
// to the reference-processing phase. Since all current
|
|
// time-stamp policies advance the soft-ref clock only
|
|
// at a major collection cycle, this is always currently
|
|
// accurate.
|
|
if (!_current_soft_ref_policy->should_clear_reference(obj, _soft_ref_timestamp_clock)) {
|
|
return false;
|
|
}
|
|
}
|
|
|
|
ResourceMark rm; // Needed for tracing.
|
|
|
|
HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr(obj);
|
|
const oop discovered = java_lang_ref_Reference::discovered(obj);
|
|
assert(discovered->is_oop_or_null(), err_msg("Expected an oop or NULL for discovered field at " PTR_FORMAT, p2i(discovered)));
|
|
if (discovered != NULL) {
|
|
// The reference has already been discovered...
|
|
if (TraceReferenceGC) {
|
|
gclog_or_tty->print_cr("Already discovered reference (" INTPTR_FORMAT ": %s)",
|
|
(void *)obj, obj->klass()->internal_name());
|
|
}
|
|
if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
|
|
// assumes that an object is not processed twice;
|
|
// if it's been already discovered it must be on another
|
|
// generation's discovered list; so we won't discover it.
|
|
return false;
|
|
} else {
|
|
assert(RefDiscoveryPolicy == ReferenceBasedDiscovery,
|
|
"Unrecognized policy");
|
|
// Check assumption that an object is not potentially
|
|
// discovered twice except by concurrent collectors that potentially
|
|
// trace the same Reference object twice.
|
|
assert(UseConcMarkSweepGC || UseG1GC,
|
|
"Only possible with a concurrent marking collector");
|
|
return true;
|
|
}
|
|
}
|
|
|
|
if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
|
|
verify_referent(obj);
|
|
// Discover if and only if EITHER:
|
|
// .. reference is in our span, OR
|
|
// .. we are an atomic collector and referent is in our span
|
|
if (_span.contains(obj_addr) ||
|
|
(discovery_is_atomic() &&
|
|
_span.contains(java_lang_ref_Reference::referent(obj)))) {
|
|
// should_enqueue = true;
|
|
} else {
|
|
return false;
|
|
}
|
|
} else {
|
|
assert(RefDiscoveryPolicy == ReferenceBasedDiscovery &&
|
|
_span.contains(obj_addr), "code inconsistency");
|
|
}
|
|
|
|
// Get the right type of discovered queue head.
|
|
DiscoveredList* list = get_discovered_list(rt);
|
|
if (list == NULL) {
|
|
return false; // nothing special needs to be done
|
|
}
|
|
|
|
if (_discovery_is_mt) {
|
|
add_to_discovered_list_mt(*list, obj, discovered_addr);
|
|
} else {
|
|
// We do a raw store here: the field will be visited later when processing
|
|
// the discovered references.
|
|
oop current_head = list->head();
|
|
// The last ref must have its discovered field pointing to itself.
|
|
oop next_discovered = (current_head != NULL) ? current_head : obj;
|
|
|
|
assert(discovered == NULL, "control point invariant");
|
|
oop_store_raw(discovered_addr, next_discovered);
|
|
list->set_head(obj);
|
|
list->inc_length(1);
|
|
|
|
if (TraceReferenceGC) {
|
|
gclog_or_tty->print_cr("Discovered reference (" INTPTR_FORMAT ": %s)",
|
|
(void *)obj, obj->klass()->internal_name());
|
|
}
|
|
}
|
|
assert(obj->is_oop(), "Discovered a bad reference");
|
|
verify_referent(obj);
|
|
return true;
|
|
}
|
|
|
|
// Preclean the discovered references by removing those
|
|
// whose referents are alive, and by marking from those that
|
|
// are not active. These lists can be handled here
|
|
// in any order and, indeed, concurrently.
|
|
void ReferenceProcessor::preclean_discovered_references(
|
|
BoolObjectClosure* is_alive,
|
|
OopClosure* keep_alive,
|
|
VoidClosure* complete_gc,
|
|
YieldClosure* yield,
|
|
GCTimer* gc_timer,
|
|
GCId gc_id) {
|
|
|
|
NOT_PRODUCT(verify_ok_to_handle_reflists());
|
|
|
|
// Soft references
|
|
{
|
|
GCTraceTime tt("Preclean SoftReferences", PrintGCDetails && PrintReferenceGC,
|
|
false, gc_timer, gc_id);
|
|
for (uint i = 0; i < _max_num_q; i++) {
|
|
if (yield->should_return()) {
|
|
return;
|
|
}
|
|
preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive,
|
|
keep_alive, complete_gc, yield);
|
|
}
|
|
}
|
|
|
|
// Weak references
|
|
{
|
|
GCTraceTime tt("Preclean WeakReferences", PrintGCDetails && PrintReferenceGC,
|
|
false, gc_timer, gc_id);
|
|
for (uint i = 0; i < _max_num_q; i++) {
|
|
if (yield->should_return()) {
|
|
return;
|
|
}
|
|
preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive,
|
|
keep_alive, complete_gc, yield);
|
|
}
|
|
}
|
|
|
|
// Final references
|
|
{
|
|
GCTraceTime tt("Preclean FinalReferences", PrintGCDetails && PrintReferenceGC,
|
|
false, gc_timer, gc_id);
|
|
for (uint i = 0; i < _max_num_q; i++) {
|
|
if (yield->should_return()) {
|
|
return;
|
|
}
|
|
preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive,
|
|
keep_alive, complete_gc, yield);
|
|
}
|
|
}
|
|
|
|
// Phantom references
|
|
{
|
|
GCTraceTime tt("Preclean PhantomReferences", PrintGCDetails && PrintReferenceGC,
|
|
false, gc_timer, gc_id);
|
|
for (uint i = 0; i < _max_num_q; i++) {
|
|
if (yield->should_return()) {
|
|
return;
|
|
}
|
|
preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive,
|
|
keep_alive, complete_gc, yield);
|
|
}
|
|
}
|
|
}
|
|
|
|
// Walk the given discovered ref list, and remove all reference objects
|
|
// whose referents are still alive, whose referents are NULL or which
|
|
// are not active (have a non-NULL next field). NOTE: When we are
|
|
// thus precleaning the ref lists (which happens single-threaded today),
|
|
// we do not disable refs discovery to honor the correct semantics of
|
|
// java.lang.Reference. As a result, we need to be careful below
|
|
// that ref removal steps interleave safely with ref discovery steps
|
|
// (in this thread).
|
|
void
|
|
ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list,
|
|
BoolObjectClosure* is_alive,
|
|
OopClosure* keep_alive,
|
|
VoidClosure* complete_gc,
|
|
YieldClosure* yield) {
|
|
DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
|
|
while (iter.has_next()) {
|
|
iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
|
|
oop obj = iter.obj();
|
|
oop next = java_lang_ref_Reference::next(obj);
|
|
if (iter.referent() == NULL || iter.is_referent_alive() ||
|
|
next != NULL) {
|
|
// The referent has been cleared, or is alive, or the Reference is not
|
|
// active; we need to trace and mark its cohort.
|
|
if (TraceReferenceGC) {
|
|
gclog_or_tty->print_cr("Precleaning Reference (" INTPTR_FORMAT ": %s)",
|
|
(void *)iter.obj(), iter.obj()->klass()->internal_name());
|
|
}
|
|
// Remove Reference object from list
|
|
iter.remove();
|
|
// Keep alive its cohort.
|
|
iter.make_referent_alive();
|
|
if (UseCompressedOops) {
|
|
narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr(obj);
|
|
keep_alive->do_oop(next_addr);
|
|
} else {
|
|
oop* next_addr = (oop*)java_lang_ref_Reference::next_addr(obj);
|
|
keep_alive->do_oop(next_addr);
|
|
}
|
|
iter.move_to_next();
|
|
} else {
|
|
iter.next();
|
|
}
|
|
}
|
|
// Close the reachable set
|
|
complete_gc->do_void();
|
|
|
|
NOT_PRODUCT(
|
|
if (PrintGCDetails && PrintReferenceGC && (iter.processed() > 0)) {
|
|
gclog_or_tty->print_cr(" Dropped %d Refs out of %d "
|
|
"Refs in discovered list " INTPTR_FORMAT,
|
|
iter.removed(), iter.processed(), (address)refs_list.head());
|
|
}
|
|
)
|
|
}
|
|
|
|
const char* ReferenceProcessor::list_name(uint i) {
|
|
assert(i >= 0 && i <= _max_num_q * number_of_subclasses_of_ref(),
|
|
"Out of bounds index");
|
|
|
|
int j = i / _max_num_q;
|
|
switch (j) {
|
|
case 0: return "SoftRef";
|
|
case 1: return "WeakRef";
|
|
case 2: return "FinalRef";
|
|
case 3: return "PhantomRef";
|
|
}
|
|
ShouldNotReachHere();
|
|
return NULL;
|
|
}
|
|
|
|
#ifndef PRODUCT
|
|
void ReferenceProcessor::verify_ok_to_handle_reflists() {
|
|
// empty for now
|
|
}
|
|
#endif
|
|
|
|
#ifndef PRODUCT
|
|
void ReferenceProcessor::clear_discovered_references() {
|
|
guarantee(!_discovering_refs, "Discovering refs?");
|
|
for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
|
|
clear_discovered_references(_discovered_refs[i]);
|
|
}
|
|
}
|
|
|
|
#endif // PRODUCT
|