--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/hotspot/src/share/vm/gc/shared/referenceProcessor.cpp Wed May 13 15:16:06 2015 +0200
@@ -0,0 +1,1314 @@
+/*
+ * Copyright (c) 2001, 2015, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#include "precompiled.hpp"
+#include "classfile/javaClasses.hpp"
+#include "classfile/systemDictionary.hpp"
+#include "gc/shared/collectedHeap.hpp"
+#include "gc/shared/collectedHeap.inline.hpp"
+#include "gc/shared/gcTimer.hpp"
+#include "gc/shared/gcTraceTime.hpp"
+#include "gc/shared/referencePolicy.hpp"
+#include "gc/shared/referenceProcessor.hpp"
+#include "oops/oop.inline.hpp"
+#include "runtime/java.hpp"
+#include "runtime/jniHandles.hpp"
+
+ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL;
+ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = NULL;
+jlong ReferenceProcessor::_soft_ref_timestamp_clock = 0;
+
+void referenceProcessor_init() {
+ ReferenceProcessor::init_statics();
+}
+
+void ReferenceProcessor::init_statics() {
+ // We need a monotonically non-decreasing time in ms but
+ // os::javaTimeMillis() does not guarantee monotonicity.
+ jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
+
+ // Initialize the soft ref timestamp clock.
+ _soft_ref_timestamp_clock = now;
+ // Also update the soft ref clock in j.l.r.SoftReference
+ java_lang_ref_SoftReference::set_clock(_soft_ref_timestamp_clock);
+
+ _always_clear_soft_ref_policy = new AlwaysClearPolicy();
+ _default_soft_ref_policy = new COMPILER2_PRESENT(LRUMaxHeapPolicy())
+ NOT_COMPILER2(LRUCurrentHeapPolicy());
+ if (_always_clear_soft_ref_policy == NULL || _default_soft_ref_policy == NULL) {
+ vm_exit_during_initialization("Could not allocate reference policy object");
+ }
+ guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery ||
+ RefDiscoveryPolicy == ReferentBasedDiscovery,
+ "Unrecognized RefDiscoveryPolicy");
+}
+
+void ReferenceProcessor::enable_discovery(bool check_no_refs) {
+#ifdef ASSERT
+ // Verify that we're not currently discovering refs
+ assert(!_discovering_refs, "nested call?");
+
+ if (check_no_refs) {
+ // Verify that the discovered lists are empty
+ verify_no_references_recorded();
+ }
+#endif // ASSERT
+
+ // Someone could have modified the value of the static
+ // field in the j.l.r.SoftReference class that holds the
+ // soft reference timestamp clock using reflection or
+ // Unsafe between GCs. Unconditionally update the static
+ // field in ReferenceProcessor here so that we use the new
+ // value during reference discovery.
+
+ _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
+ _discovering_refs = true;
+}
+
+ReferenceProcessor::ReferenceProcessor(MemRegion span,
+ bool mt_processing,
+ uint mt_processing_degree,
+ bool mt_discovery,
+ uint mt_discovery_degree,
+ bool atomic_discovery,
+ BoolObjectClosure* is_alive_non_header) :
+ _discovering_refs(false),
+ _enqueuing_is_done(false),
+ _is_alive_non_header(is_alive_non_header),
+ _processing_is_mt(mt_processing),
+ _next_id(0)
+{
+ _span = span;
+ _discovery_is_atomic = atomic_discovery;
+ _discovery_is_mt = mt_discovery;
+ _num_q = MAX2(1U, mt_processing_degree);
+ _max_num_q = MAX2(_num_q, mt_discovery_degree);
+ _discovered_refs = NEW_C_HEAP_ARRAY(DiscoveredList,
+ _max_num_q * number_of_subclasses_of_ref(), mtGC);
+
+ if (_discovered_refs == NULL) {
+ vm_exit_during_initialization("Could not allocated RefProc Array");
+ }
+ _discoveredSoftRefs = &_discovered_refs[0];
+ _discoveredWeakRefs = &_discoveredSoftRefs[_max_num_q];
+ _discoveredFinalRefs = &_discoveredWeakRefs[_max_num_q];
+ _discoveredPhantomRefs = &_discoveredFinalRefs[_max_num_q];
+ _discoveredCleanerRefs = &_discoveredPhantomRefs[_max_num_q];
+
+ // Initialize all entries to NULL
+ for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
+ _discovered_refs[i].set_head(NULL);
+ _discovered_refs[i].set_length(0);
+ }
+
+ setup_policy(false /* default soft ref policy */);
+}
+
+#ifndef PRODUCT
+void ReferenceProcessor::verify_no_references_recorded() {
+ guarantee(!_discovering_refs, "Discovering refs?");
+ for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
+ guarantee(_discovered_refs[i].is_empty(),
+ "Found non-empty discovered list");
+ }
+}
+#endif
+
+void ReferenceProcessor::weak_oops_do(OopClosure* f) {
+ for (uint i = 0; i < _max_num_q * number_of_subclasses_of_ref(); i++) {
+ if (UseCompressedOops) {
+ f->do_oop((narrowOop*)_discovered_refs[i].adr_head());
+ } else {
+ f->do_oop((oop*)_discovered_refs[i].adr_head());
+ }
+ }
+}
+
+void ReferenceProcessor::update_soft_ref_master_clock() {
+ // Update (advance) the soft ref master clock field. This must be done
+ // after processing the soft ref list.
+
+ // We need a monotonically non-decreasing time in ms but
+ // os::javaTimeMillis() does not guarantee monotonicity.
+ jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
+ jlong soft_ref_clock = java_lang_ref_SoftReference::clock();
+ assert(soft_ref_clock == _soft_ref_timestamp_clock, "soft ref clocks out of sync");
+
+ NOT_PRODUCT(
+ if (now < _soft_ref_timestamp_clock) {
+ warning("time warp: " JLONG_FORMAT " to " JLONG_FORMAT,
+ _soft_ref_timestamp_clock, now);
+ }
+ )
+ // The values of now and _soft_ref_timestamp_clock are set using
+ // javaTimeNanos(), which is guaranteed to be monotonically
+ // non-decreasing provided the underlying platform provides such
+ // a time source (and it is bug free).
+ // In product mode, however, protect ourselves from non-monotonicity.
+ if (now > _soft_ref_timestamp_clock) {
+ _soft_ref_timestamp_clock = now;
+ java_lang_ref_SoftReference::set_clock(now);
+ }
+ // Else leave clock stalled at its old value until time progresses
+ // past clock value.
+}
+
+size_t ReferenceProcessor::total_count(DiscoveredList lists[]) {
+ size_t total = 0;
+ for (uint i = 0; i < _max_num_q; ++i) {
+ total += lists[i].length();
+ }
+ return total;
+}
+
+ReferenceProcessorStats ReferenceProcessor::process_discovered_references(
+ BoolObjectClosure* is_alive,
+ OopClosure* keep_alive,
+ VoidClosure* complete_gc,
+ AbstractRefProcTaskExecutor* task_executor,
+ GCTimer* gc_timer,
+ GCId gc_id) {
+ NOT_PRODUCT(verify_ok_to_handle_reflists());
+
+ assert(!enqueuing_is_done(), "If here enqueuing should not be complete");
+ // Stop treating discovered references specially.
+ disable_discovery();
+
+ // If discovery was concurrent, someone could have modified
+ // the value of the static field in the j.l.r.SoftReference
+ // class that holds the soft reference timestamp clock using
+ // reflection or Unsafe between when discovery was enabled and
+ // now. Unconditionally update the static field in ReferenceProcessor
+ // here so that we use the new value during processing of the
+ // discovered soft refs.
+
+ _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock();
+
+ bool trace_time = PrintGCDetails && PrintReferenceGC;
+
+ // Soft references
+ size_t soft_count = 0;
+ {
+ GCTraceTime tt("SoftReference", trace_time, false, gc_timer, gc_id);
+ soft_count =
+ process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true,
+ is_alive, keep_alive, complete_gc, task_executor);
+ }
+
+ update_soft_ref_master_clock();
+
+ // Weak references
+ size_t weak_count = 0;
+ {
+ GCTraceTime tt("WeakReference", trace_time, false, gc_timer, gc_id);
+ weak_count =
+ process_discovered_reflist(_discoveredWeakRefs, NULL, true,
+ is_alive, keep_alive, complete_gc, task_executor);
+ }
+
+ // Final references
+ size_t final_count = 0;
+ {
+ GCTraceTime tt("FinalReference", trace_time, false, gc_timer, gc_id);
+ final_count =
+ process_discovered_reflist(_discoveredFinalRefs, NULL, false,
+ is_alive, keep_alive, complete_gc, task_executor);
+ }
+
+ // Phantom references
+ size_t phantom_count = 0;
+ {
+ GCTraceTime tt("PhantomReference", trace_time, false, gc_timer, gc_id);
+ phantom_count =
+ process_discovered_reflist(_discoveredPhantomRefs, NULL, false,
+ is_alive, keep_alive, complete_gc, task_executor);
+
+ // Process cleaners, but include them in phantom statistics. We expect
+ // Cleaner references to be temporary, and don't want to deal with
+ // possible incompatibilities arising from making it more visible.
+ phantom_count +=
+ process_discovered_reflist(_discoveredCleanerRefs, NULL, true,
+ is_alive, keep_alive, complete_gc, task_executor);
+ }
+
+ // Weak global JNI references. It would make more sense (semantically) to
+ // traverse these simultaneously with the regular weak references above, but
+ // that is not how the JDK1.2 specification is. See #4126360. Native code can
+ // thus use JNI weak references to circumvent the phantom references and
+ // resurrect a "post-mortem" object.
+ {
+ GCTraceTime tt("JNI Weak Reference", trace_time, false, gc_timer, gc_id);
+ if (task_executor != NULL) {
+ task_executor->set_single_threaded_mode();
+ }
+ process_phaseJNI(is_alive, keep_alive, complete_gc);
+ }
+
+ return ReferenceProcessorStats(soft_count, weak_count, final_count, phantom_count);
+}
+
+#ifndef PRODUCT
+// Calculate the number of jni handles.
+uint ReferenceProcessor::count_jni_refs() {
+ class AlwaysAliveClosure: public BoolObjectClosure {
+ public:
+ virtual bool do_object_b(oop obj) { return true; }
+ };
+
+ class CountHandleClosure: public OopClosure {
+ private:
+ int _count;
+ public:
+ CountHandleClosure(): _count(0) {}
+ void do_oop(oop* unused) { _count++; }
+ void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
+ int count() { return _count; }
+ };
+ CountHandleClosure global_handle_count;
+ AlwaysAliveClosure always_alive;
+ JNIHandles::weak_oops_do(&always_alive, &global_handle_count);
+ return global_handle_count.count();
+}
+#endif
+
+void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive,
+ OopClosure* keep_alive,
+ VoidClosure* complete_gc) {
+#ifndef PRODUCT
+ if (PrintGCDetails && PrintReferenceGC) {
+ unsigned int count = count_jni_refs();
+ gclog_or_tty->print(", %u refs", count);
+ }
+#endif
+ JNIHandles::weak_oops_do(is_alive, keep_alive);
+ complete_gc->do_void();
+}
+
+
+template <class T>
+bool enqueue_discovered_ref_helper(ReferenceProcessor* ref,
+ AbstractRefProcTaskExecutor* task_executor) {
+
+ // Remember old value of pending references list
+ T* pending_list_addr = (T*)java_lang_ref_Reference::pending_list_addr();
+ T old_pending_list_value = *pending_list_addr;
+
+ // Enqueue references that are not made active again, and
+ // clear the decks for the next collection (cycle).
+ ref->enqueue_discovered_reflists((HeapWord*)pending_list_addr, task_executor);
+ // Do the post-barrier on pending_list_addr missed in
+ // enqueue_discovered_reflist.
+ oopDesc::bs()->write_ref_field(pending_list_addr, oopDesc::load_decode_heap_oop(pending_list_addr));
+
+ // Stop treating discovered references specially.
+ ref->disable_discovery();
+
+ // Return true if new pending references were added
+ return old_pending_list_value != *pending_list_addr;
+}
+
+bool ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor) {
+ NOT_PRODUCT(verify_ok_to_handle_reflists());
+ if (UseCompressedOops) {
+ return enqueue_discovered_ref_helper<narrowOop>(this, task_executor);
+ } else {
+ return enqueue_discovered_ref_helper<oop>(this, task_executor);
+ }
+}
+
+void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list,
+ HeapWord* pending_list_addr) {
+ // Given a list of refs linked through the "discovered" field
+ // (java.lang.ref.Reference.discovered), self-loop their "next" field
+ // thus distinguishing them from active References, then
+ // prepend them to the pending list.
+ //
+ // The Java threads will see the Reference objects linked together through
+ // the discovered field. Instead of trying to do the write barrier updates
+ // in all places in the reference processor where we manipulate the discovered
+ // field we make sure to do the barrier here where we anyway iterate through
+ // all linked Reference objects. Note that it is important to not dirty any
+ // cards during reference processing since this will cause card table
+ // verification to fail for G1.
+ if (TraceReferenceGC && PrintGCDetails) {
+ gclog_or_tty->print_cr("ReferenceProcessor::enqueue_discovered_reflist list "
+ INTPTR_FORMAT, p2i(refs_list.head()));
+ }
+
+ oop obj = NULL;
+ oop next_d = refs_list.head();
+ // Walk down the list, self-looping the next field
+ // so that the References are not considered active.
+ while (obj != next_d) {
+ obj = next_d;
+ assert(obj->is_instanceRef(), "should be reference object");
+ next_d = java_lang_ref_Reference::discovered(obj);
+ if (TraceReferenceGC && PrintGCDetails) {
+ gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next_d " INTPTR_FORMAT,
+ p2i(obj), p2i(next_d));
+ }
+ assert(java_lang_ref_Reference::next(obj) == NULL,
+ "Reference not active; should not be discovered");
+ // Self-loop next, so as to make Ref not active.
+ java_lang_ref_Reference::set_next_raw(obj, obj);
+ if (next_d != obj) {
+ oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), next_d);
+ } else {
+ // This is the last object.
+ // Swap refs_list into pending_list_addr and
+ // set obj's discovered to what we read from pending_list_addr.
+ oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr);
+ // Need post-barrier on pending_list_addr. See enqueue_discovered_ref_helper() above.
+ java_lang_ref_Reference::set_discovered_raw(obj, old); // old may be NULL
+ oopDesc::bs()->write_ref_field(java_lang_ref_Reference::discovered_addr(obj), old);
+ }
+ }
+}
+
+// Parallel enqueue task
+class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask {
+public:
+ RefProcEnqueueTask(ReferenceProcessor& ref_processor,
+ DiscoveredList discovered_refs[],
+ HeapWord* pending_list_addr,
+ int n_queues)
+ : EnqueueTask(ref_processor, discovered_refs,
+ pending_list_addr, n_queues)
+ { }
+
+ virtual void work(unsigned int work_id) {
+ assert(work_id < (unsigned int)_ref_processor.max_num_q(), "Index out-of-bounds");
+ // Simplest first cut: static partitioning.
+ int index = work_id;
+ // The increment on "index" must correspond to the maximum number of queues
+ // (n_queues) with which that ReferenceProcessor was created. That
+ // is because of the "clever" way the discovered references lists were
+ // allocated and are indexed into.
+ assert(_n_queues == (int) _ref_processor.max_num_q(), "Different number not expected");
+ for (int j = 0;
+ j < ReferenceProcessor::number_of_subclasses_of_ref();
+ j++, index += _n_queues) {
+ _ref_processor.enqueue_discovered_reflist(
+ _refs_lists[index], _pending_list_addr);
+ _refs_lists[index].set_head(NULL);
+ _refs_lists[index].set_length(0);
+ }
+ }
+};
+
+// 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);
+}
+
+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",
+ p2i(iter.obj()), iter.obj()->klass()->internal_name());
+ }
+ // Remove Reference object from list
+ iter.remove();
+ // 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 " SIZE_FORMAT " dead Refs out of " SIZE_FORMAT
+ " discovered Refs by policy, from list " INTPTR_FORMAT,
+ iter.removed(), iter.processed(), p2i(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)",
+ p2i(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 " SIZE_FORMAT " active Refs out of " SIZE_FORMAT
+ " Refs in discovered list " INTPTR_FORMAT,
+ iter.removed(), iter.processed(), p2i(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 " SIZE_FORMAT " active Refs out of " SIZE_FORMAT
+ " Refs in discovered list " INTPTR_FORMAT,
+ iter.removed(), iter.processed(), p2i(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.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 " : "",
+ p2i(iter.obj()), iter.obj()->klass()->internal_name());
+ }
+ assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference");
+ iter.next();
+ }
+ // 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(SIZE_FORMAT " ", ref_lists[i].length());
+ }
+ }
+ if (TraceReferenceGC && PrintGCDetails) {
+ gclog_or_tty->print_cr(" = " SIZE_FORMAT, 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(SIZE_FORMAT " ", ref_lists[i].length());
+ }
+ }
+ if (TraceReferenceGC && PrintGCDetails) {
+ gclog_or_tty->print_cr(" = " SIZE_FORMAT, 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);
+ balance_queues(_discoveredCleanerRefs);
+}
+
+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(", " SIZE_FORMAT " 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(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_CLEANER:
+ list = &_discoveredCleanerRefs[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, p2i(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)",
+ p2i(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)",
+ p2i(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 ",
+ p2i(referent), p2i(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)",
+ p2i(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)",
+ p2i(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);
+ }
+
+ // Cleaner references. Included in timing for phantom references. We
+ // expect Cleaner references to be temporary, and don't want to deal with
+ // possible incompatibilities arising from making it more visible.
+ for (uint i = 0; i < _max_num_q; i++) {
+ if (yield->should_return()) {
+ return;
+ }
+ preclean_discovered_reflist(_discoveredCleanerRefs[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)",
+ p2i(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 " SIZE_FORMAT " Refs out of " SIZE_FORMAT
+ " Refs in discovered list " INTPTR_FORMAT,
+ iter.removed(), iter.processed(), p2i(refs_list.head()));
+ }
+ )
+}
+
+const char* ReferenceProcessor::list_name(uint i) {
+ assert(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";
+ case 4: return "CleanerRef";
+ }
+ 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