--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/hotspot/src/share/vm/memory/referenceProcessor.cpp Sat Dec 01 00:00:00 2007 +0000
@@ -0,0 +1,1261 @@
+/*
+ * Copyright 2001-2007 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ *
+ */
+
+# include "incls/_precompiled.incl"
+# include "incls/_referenceProcessor.cpp.incl"
+
+// List of discovered references.
+class DiscoveredList {
+public:
+ DiscoveredList() : _head(NULL), _len(0) { }
+ oop head() const { return _head; }
+ oop* head_ptr() { return &_head; }
+ void set_head(oop o) { _head = o; }
+ bool empty() const { return _head == ReferenceProcessor::_sentinelRef; }
+ size_t length() { return _len; }
+ void set_length(size_t len) { _len = len; }
+private:
+ size_t _len;
+ oop _head;
+};
+
+oop ReferenceProcessor::_sentinelRef = NULL;
+
+const int subclasses_of_ref = REF_PHANTOM - REF_OTHER;
+
+void referenceProcessor_init() {
+ ReferenceProcessor::init_statics();
+}
+
+void ReferenceProcessor::init_statics() {
+ assert(_sentinelRef == NULL, "should be initialized precsiely once");
+ EXCEPTION_MARK;
+ _sentinelRef = instanceKlass::cast(
+ SystemDictionary::object_klass())->
+ allocate_permanent_instance(THREAD);
+
+ // Initialize the master soft ref clock.
+ java_lang_ref_SoftReference::set_clock(os::javaTimeMillis());
+
+ if (HAS_PENDING_EXCEPTION) {
+ Handle ex(THREAD, PENDING_EXCEPTION);
+ vm_exit_during_initialization(ex);
+ }
+ assert(_sentinelRef != NULL && _sentinelRef->is_oop(),
+ "Just constructed it!");
+ guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery ||
+ RefDiscoveryPolicy == ReferentBasedDiscovery,
+ "Unrecongnized RefDiscoveryPolicy");
+}
+
+
+ReferenceProcessor* ReferenceProcessor::create_ref_processor(
+ MemRegion span,
+ bool atomic_discovery,
+ bool mt_discovery,
+ BoolObjectClosure* is_alive_non_header,
+ int parallel_gc_threads,
+ bool mt_processing)
+{
+ int mt_degree = 1;
+ if (parallel_gc_threads > 1) {
+ mt_degree = parallel_gc_threads;
+ }
+ ReferenceProcessor* rp =
+ new ReferenceProcessor(span, atomic_discovery,
+ mt_discovery, mt_degree,
+ mt_processing);
+ if (rp == NULL) {
+ vm_exit_during_initialization("Could not allocate ReferenceProcessor object");
+ }
+ rp->set_is_alive_non_header(is_alive_non_header);
+ return rp;
+}
+
+
+ReferenceProcessor::ReferenceProcessor(MemRegion span,
+ bool atomic_discovery, bool mt_discovery, int mt_degree,
+ bool mt_processing) :
+ _discovering_refs(false),
+ _enqueuing_is_done(false),
+ _is_alive_non_header(NULL),
+ _processing_is_mt(mt_processing),
+ _next_id(0)
+{
+ _span = span;
+ _discovery_is_atomic = atomic_discovery;
+ _discovery_is_mt = mt_discovery;
+ _num_q = mt_degree;
+ _discoveredSoftRefs = NEW_C_HEAP_ARRAY(DiscoveredList, _num_q * subclasses_of_ref);
+ if (_discoveredSoftRefs == NULL) {
+ vm_exit_during_initialization("Could not allocated RefProc Array");
+ }
+ _discoveredWeakRefs = &_discoveredSoftRefs[_num_q];
+ _discoveredFinalRefs = &_discoveredWeakRefs[_num_q];
+ _discoveredPhantomRefs = &_discoveredFinalRefs[_num_q];
+ assert(_sentinelRef != NULL, "_sentinelRef is NULL");
+ // Initialized all entries to _sentinelRef
+ for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
+ _discoveredSoftRefs[i].set_head(_sentinelRef);
+ _discoveredSoftRefs[i].set_length(0);
+ }
+}
+
+#ifndef PRODUCT
+void ReferenceProcessor::verify_no_references_recorded() {
+ guarantee(!_discovering_refs, "Discovering refs?");
+ for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
+ guarantee(_discoveredSoftRefs[i].empty(),
+ "Found non-empty discovered list");
+ }
+}
+#endif
+
+void ReferenceProcessor::weak_oops_do(OopClosure* f) {
+ for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
+ f->do_oop(_discoveredSoftRefs[i].head_ptr());
+ }
+}
+
+void ReferenceProcessor::oops_do(OopClosure* f) {
+ f->do_oop(&_sentinelRef);
+}
+
+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.
+ jlong now = os::javaTimeMillis();
+ jlong clock = java_lang_ref_SoftReference::clock();
+ NOT_PRODUCT(
+ if (now < clock) {
+ warning("time warp: %d to %d", clock, now);
+ }
+ )
+ // In product mode, protect ourselves from system time being adjusted
+ // externally and going backward; see note in the implementation of
+ // GenCollectedHeap::time_since_last_gc() for the right way to fix
+ // this uniformly throughout the VM; see bug-id 4741166. XXX
+ if (now > clock) {
+ java_lang_ref_SoftReference::set_clock(now);
+ }
+ // Else leave clock stalled at its old value until time progresses
+ // past clock value.
+}
+
+
+void
+ReferenceProcessor::process_discovered_references(
+ ReferencePolicy* policy,
+ BoolObjectClosure* is_alive,
+ OopClosure* keep_alive,
+ VoidClosure* complete_gc,
+ AbstractRefProcTaskExecutor* task_executor) {
+ 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();
+
+ bool trace_time = PrintGCDetails && PrintReferenceGC;
+ // Soft references
+ {
+ TraceTime tt("SoftReference", trace_time, false, gclog_or_tty);
+ process_discovered_reflist(_discoveredSoftRefs, policy, true,
+ is_alive, keep_alive, complete_gc, task_executor);
+ }
+
+ update_soft_ref_master_clock();
+
+ // Weak references
+ {
+ TraceTime tt("WeakReference", trace_time, false, gclog_or_tty);
+ process_discovered_reflist(_discoveredWeakRefs, NULL, true,
+ is_alive, keep_alive, complete_gc, task_executor);
+ }
+
+ // Final references
+ {
+ TraceTime tt("FinalReference", trace_time, false, gclog_or_tty);
+ process_discovered_reflist(_discoveredFinalRefs, NULL, false,
+ is_alive, keep_alive, complete_gc, task_executor);
+ }
+
+ // Phantom references
+ {
+ TraceTime tt("PhantomReference", trace_time, false, gclog_or_tty);
+ process_discovered_reflist(_discoveredPhantomRefs, NULL, false,
+ 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.
+ {
+ TraceTime tt("JNI Weak Reference", trace_time, false, gclog_or_tty);
+ if (task_executor != NULL) {
+ task_executor->set_single_threaded_mode();
+ }
+ process_phaseJNI(is_alive, keep_alive, complete_gc);
+ }
+}
+
+
+#ifndef PRODUCT
+// Calculate the number of jni handles.
+unsigned int ReferenceProcessor::count_jni_refs()
+{
+ class AlwaysAliveClosure: public BoolObjectClosure {
+ public:
+ bool do_object_b(oop obj) { return true; }
+ void do_object(oop obj) { assert(false, "Don't call"); }
+ };
+
+ class CountHandleClosure: public OopClosure {
+ private:
+ int _count;
+ public:
+ CountHandleClosure(): _count(0) {}
+ void do_oop(oop* unused) {
+ _count++;
+ }
+ 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);
+ // Finally remember to keep sentinel around
+ keep_alive->do_oop(&_sentinelRef);
+ complete_gc->do_void();
+}
+
+bool ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor) {
+ NOT_PRODUCT(verify_ok_to_handle_reflists());
+ // Remember old value of pending references list
+ oop* pending_list_addr = java_lang_ref_Reference::pending_list_addr();
+ oop old_pending_list_value = *pending_list_addr;
+
+ // Enqueue references that are not made active again, and
+ // clear the decks for the next collection (cycle).
+ enqueue_discovered_reflists(pending_list_addr, task_executor);
+ // Do the oop-check on pending_list_addr missed in
+ // enqueue_discovered_reflist. We should probably
+ // do a raw oop_check so that future such idempotent
+ // oop_stores relying on the oop-check side-effect
+ // may be elided automatically and safely without
+ // affecting correctness.
+ oop_store(pending_list_addr, *(pending_list_addr));
+
+ // Stop treating discovered references specially.
+ disable_discovery();
+
+ // Return true if new pending references were added
+ return old_pending_list_value != *pending_list_addr;
+}
+
+void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list,
+ oop* pending_list_addr) {
+ // Given a list of refs linked through the "discovered" field
+ // (java.lang.ref.Reference.discovered) chain them through the
+ // "next" field (java.lang.ref.Reference.next) and prepend
+ // to the pending list.
+ if (TraceReferenceGC && PrintGCDetails) {
+ gclog_or_tty->print_cr("ReferenceProcessor::enqueue_discovered_reflist list "
+ INTPTR_FORMAT, (address)refs_list.head());
+ }
+ oop obj = refs_list.head();
+ // Walk down the list, copying the discovered field into
+ // the next field and clearing it (except for the last
+ // non-sentinel object which is treated specially to avoid
+ // confusion with an active reference).
+ while (obj != _sentinelRef) {
+ assert(obj->is_instanceRef(), "should be reference object");
+ oop next = java_lang_ref_Reference::discovered(obj);
+ if (TraceReferenceGC && PrintGCDetails) {
+ gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next " INTPTR_FORMAT,
+ (oopDesc*) obj, (oopDesc*) next);
+ }
+ assert(*java_lang_ref_Reference::next_addr(obj) == NULL,
+ "The reference should not be enqueued");
+ if (next == _sentinelRef) { // obj is last
+ // Swap refs_list into pendling_list_addr and
+ // set obj's next to what we read from pending_list_addr.
+ oop old = (oop)Atomic::xchg_ptr(refs_list.head(), pending_list_addr);
+ // Need oop_check on pending_list_addr above;
+ // see special oop-check code at the end of
+ // enqueue_discovered_reflists() further below.
+ if (old == NULL) {
+ // obj should be made to point to itself, since
+ // pending list was empty.
+ java_lang_ref_Reference::set_next(obj, obj);
+ } else {
+ java_lang_ref_Reference::set_next(obj, old);
+ }
+ } else {
+ java_lang_ref_Reference::set_next(obj, next);
+ }
+ java_lang_ref_Reference::set_discovered(obj, (oop) NULL);
+ obj = next;
+ }
+}
+
+// Parallel enqueue task
+class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask {
+public:
+ RefProcEnqueueTask(ReferenceProcessor& ref_processor,
+ DiscoveredList discovered_refs[],
+ oop* pending_list_addr,
+ oop sentinel_ref,
+ int n_queues)
+ : EnqueueTask(ref_processor, discovered_refs,
+ pending_list_addr, sentinel_ref, n_queues)
+ { }
+
+ virtual void work(unsigned int work_id)
+ {
+ assert(work_id < (unsigned int)_ref_processor.num_q(), "Index out-of-bounds");
+ // Simplest first cut: static partitioning.
+ int index = work_id;
+ for (int j = 0; j < subclasses_of_ref; j++, index += _n_queues) {
+ _ref_processor.enqueue_discovered_reflist(
+ _refs_lists[index], _pending_list_addr);
+ _refs_lists[index].set_head(_sentinel_ref);
+ _refs_lists[index].set_length(0);
+ }
+ }
+};
+
+// Enqueue references that are not made active again
+void ReferenceProcessor::enqueue_discovered_reflists(oop* pending_list_addr,
+ AbstractRefProcTaskExecutor* task_executor) {
+ if (_processing_is_mt && task_executor != NULL) {
+ // Parallel code
+ RefProcEnqueueTask tsk(*this, _discoveredSoftRefs,
+ pending_list_addr, _sentinelRef, _num_q);
+ task_executor->execute(tsk);
+ } else {
+ // Serial code: call the parent class's implementation
+ for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
+ enqueue_discovered_reflist(_discoveredSoftRefs[i], pending_list_addr);
+ _discoveredSoftRefs[i].set_head(_sentinelRef);
+ _discoveredSoftRefs[i].set_length(0);
+ }
+ }
+}
+
+// Iterator for the list of discovered references.
+class DiscoveredListIterator {
+public:
+ inline DiscoveredListIterator(DiscoveredList& refs_list,
+ OopClosure* keep_alive,
+ BoolObjectClosure* is_alive);
+
+ // End Of List.
+ inline bool has_next() const
+ { return _next != ReferenceProcessor::_sentinelRef; }
+
+ // Get oop to the Reference object.
+ inline oop obj() const { return _ref; }
+
+ // Get oop to the referent object.
+ inline oop referent() const { return _referent; }
+
+ // Returns true if referent is alive.
+ inline bool is_referent_alive() const;
+
+ // Loads data for the current reference.
+ // The "allow_null_referent" argument tells us to allow for the possibility
+ // of a NULL referent in the discovered Reference object. This typically
+ // happens in the case of concurrent collectors that may have done the
+ // discovery concurrently or interleaved with mutator execution.
+ inline void load_ptrs(DEBUG_ONLY(bool allow_null_referent));
+
+ // Move to the next discovered reference.
+ inline void next();
+
+ // Remove the current reference from the list and move to the next.
+ inline void remove();
+
+ // Make the Reference object active again.
+ inline void make_active() { java_lang_ref_Reference::set_next(_ref, NULL); }
+
+ // Make the referent alive.
+ inline void make_referent_alive() { _keep_alive->do_oop(_referent_addr); }
+
+ // Update the discovered field.
+ inline void update_discovered() { _keep_alive->do_oop(_prev_next); }
+
+ // NULL out referent pointer.
+ inline void clear_referent() { *_referent_addr = NULL; }
+
+ // Statistics
+ NOT_PRODUCT(
+ inline size_t processed() const { return _processed; }
+ inline size_t removed() const { return _removed; }
+ )
+
+private:
+ inline void move_to_next();
+
+private:
+ DiscoveredList& _refs_list;
+ oop* _prev_next;
+ oop _ref;
+ oop* _discovered_addr;
+ oop _next;
+ oop* _referent_addr;
+ oop _referent;
+ OopClosure* _keep_alive;
+ BoolObjectClosure* _is_alive;
+ DEBUG_ONLY(
+ oop _first_seen; // cyclic linked list check
+ )
+ NOT_PRODUCT(
+ size_t _processed;
+ size_t _removed;
+ )
+};
+
+inline DiscoveredListIterator::DiscoveredListIterator(DiscoveredList& refs_list,
+ OopClosure* keep_alive,
+ BoolObjectClosure* is_alive)
+ : _refs_list(refs_list),
+ _prev_next(refs_list.head_ptr()),
+ _ref(refs_list.head()),
+#ifdef ASSERT
+ _first_seen(refs_list.head()),
+#endif
+#ifndef PRODUCT
+ _processed(0),
+ _removed(0),
+#endif
+ _next(refs_list.head()),
+ _keep_alive(keep_alive),
+ _is_alive(is_alive)
+{ }
+
+inline bool DiscoveredListIterator::is_referent_alive() const
+{
+ return _is_alive->do_object_b(_referent);
+}
+
+inline void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent))
+{
+ _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref);
+ assert(_discovered_addr && (*_discovered_addr)->is_oop_or_null(),
+ "discovered field is bad");
+ _next = *_discovered_addr;
+ _referent_addr = java_lang_ref_Reference::referent_addr(_ref);
+ _referent = *_referent_addr;
+ 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(),
+ "bad referent");
+}
+
+inline void DiscoveredListIterator::next()
+{
+ _prev_next = _discovered_addr;
+ move_to_next();
+}
+
+inline void DiscoveredListIterator::remove()
+{
+ assert(_ref->is_oop(), "Dropping a bad reference");
+ // Clear the discovered_addr field so that the object does
+ // not look like it has been discovered.
+ *_discovered_addr = NULL;
+ // Remove Reference object from list.
+ *_prev_next = _next;
+ NOT_PRODUCT(_removed++);
+ move_to_next();
+}
+
+inline void DiscoveredListIterator::move_to_next()
+{
+ _ref = _next;
+ assert(_ref != _first_seen, "cyclic ref_list found");
+ NOT_PRODUCT(_processed++);
+}
+
+
+// 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_addr,
+ ReferencePolicy* policy,
+ BoolObjectClosure* is_alive,
+ OopClosure* keep_alive,
+ VoidClosure* complete_gc) {
+ assert(policy != NULL, "Must have a non-NULL policy");
+ DiscoveredListIterator iter(refs_list_addr, 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())) {
+ if (TraceReferenceGC) {
+ gclog_or_tty->print_cr("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy",
+ (address)iter.obj(), iter.obj()->blueprint()->internal_name());
+ }
+ // Make the Reference object active again
+ iter.make_active();
+ // keep the referent around
+ iter.make_referent_alive();
+ // Remove Reference object from list
+ iter.remove();
+ } else {
+ iter.next();
+ }
+ }
+ // Close the reachable set
+ complete_gc->do_void();
+ NOT_PRODUCT(
+ if (PrintGCDetails && TraceReferenceGC) {
+ gclog_or_tty->print(" Dropped %d dead Refs out of %d "
+ "discovered Refs by policy ", iter.removed(), iter.processed());
+ }
+ )
+}
+
+// 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_addr,
+ BoolObjectClosure* is_alive,
+ OopClosure* keep_alive)
+{
+ assert(discovery_is_atomic(), "Error");
+ DiscoveredListIterator iter(refs_list_addr, keep_alive, is_alive);
+ while (iter.has_next()) {
+ iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
+ DEBUG_ONLY(oop* next_addr = java_lang_ref_Reference::next_addr(iter.obj());)
+ assert(*next_addr == 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)",
+ (address)iter.obj(), iter.obj()->blueprint()->internal_name());
+ }
+ // The referent is reachable after all.
+ // 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();
+ // Remove Reference object from list
+ iter.remove();
+ } else {
+ iter.next();
+ }
+ }
+ NOT_PRODUCT(
+ if (PrintGCDetails && TraceReferenceGC) {
+ gclog_or_tty->print(" Dropped %d active Refs out of %d "
+ "Refs in discovered list ", iter.removed(), iter.processed());
+ }
+ )
+}
+
+void
+ReferenceProcessor::pp2_work_concurrent_discovery(
+ DiscoveredList& refs_list_addr,
+ BoolObjectClosure* is_alive,
+ OopClosure* keep_alive,
+ VoidClosure* complete_gc)
+{
+ assert(!discovery_is_atomic(), "Error");
+ DiscoveredListIterator iter(refs_list_addr, keep_alive, is_alive);
+ while (iter.has_next()) {
+ iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
+ oop* next_addr = java_lang_ref_Reference::next_addr(iter.obj());
+ if ((iter.referent() == NULL || iter.is_referent_alive() ||
+ *next_addr != NULL)) {
+ assert((*next_addr)->is_oop_or_null(), "bad next field");
+ // Remove Reference object from list
+ iter.remove();
+ // Trace the cohorts
+ iter.make_referent_alive();
+ keep_alive->do_oop(next_addr);
+ } else {
+ iter.next();
+ }
+ }
+ // Now close the newly reachable set
+ complete_gc->do_void();
+ NOT_PRODUCT(
+ if (PrintGCDetails && TraceReferenceGC) {
+ gclog_or_tty->print(" Dropped %d active Refs out of %d "
+ "Refs in discovered list ", iter.removed(), iter.processed());
+ }
+ )
+}
+
+// Traverse the list and process the referents, by either
+// either clearing them or keeping them (and their reachable
+// closure) alive.
+void
+ReferenceProcessor::process_phase3(DiscoveredList& refs_list_addr,
+ bool clear_referent,
+ BoolObjectClosure* is_alive,
+ OopClosure* keep_alive,
+ VoidClosure* complete_gc) {
+ DiscoveredListIterator iter(refs_list_addr, 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 " : "",
+ (address)iter.obj(), iter.obj()->blueprint()->internal_name());
+ }
+ assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference");
+ // If discovery is concurrent, we may have objects with null referents,
+ // being those that were concurrently cleared after they were discovered
+ // (and not subsequently precleaned).
+ assert( (discovery_is_atomic() && iter.referent()->is_oop())
+ || (!discovery_is_atomic() && iter.referent()->is_oop_or_null(UseConcMarkSweepGC)),
+ "Adding a bad referent");
+ iter.next();
+ }
+ // Remember to keep sentinel pointer around
+ iter.update_discovered();
+ // Close the reachable set
+ complete_gc->do_void();
+}
+
+void
+ReferenceProcessor::abandon_partial_discovered_list(DiscoveredList& ref_list) {
+ oop obj = ref_list.head();
+ while (obj != _sentinelRef) {
+ oop* discovered_addr = java_lang_ref_Reference::discovered_addr(obj);
+ obj = *discovered_addr;
+ *discovered_addr = NULL;
+ }
+ ref_list.set_head(_sentinelRef);
+ ref_list.set_length(0);
+}
+
+void
+ReferenceProcessor::abandon_partial_discovered_list_arr(DiscoveredList refs_lists[]) {
+ for (int i = 0; i < _num_q; i++) {
+ abandon_partial_discovered_list(refs_lists[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)
+ {
+ _ref_processor.process_phase1(_refs_lists[i], _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)
+ {
+ _ref_processor.process_phase3(_refs_lists[i], _clear_referent,
+ &is_alive, &keep_alive, &complete_gc);
+ }
+private:
+ bool _clear_referent;
+};
+
+// Balances reference queues.
+void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[])
+{
+ // calculate total length
+ size_t total_refs = 0;
+ for (int i = 0; i < _num_q; ++i) {
+ total_refs += ref_lists[i].length();
+ }
+ size_t avg_refs = total_refs / _num_q + 1;
+ int to_idx = 0;
+ for (int from_idx = 0; from_idx < _num_q; from_idx++) {
+ while (ref_lists[from_idx].length() > avg_refs) {
+ assert(to_idx < _num_q, "Sanity Check!");
+ if (ref_lists[to_idx].length() < avg_refs) {
+ // move superfluous refs
+ size_t refs_to_move =
+ MIN2(ref_lists[from_idx].length() - avg_refs,
+ avg_refs - ref_lists[to_idx].length());
+ 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_addr(new_head);
+ }
+ java_lang_ref_Reference::set_discovered(move_tail, ref_lists[to_idx].head());
+ ref_lists[to_idx].set_head(move_head);
+ ref_lists[to_idx].set_length(ref_lists[to_idx].length() + refs_to_move);
+ ref_lists[from_idx].set_head(new_head);
+ ref_lists[from_idx].set_length(ref_lists[from_idx].length() - refs_to_move);
+ } else {
+ ++to_idx;
+ }
+ }
+ }
+}
+
+void
+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 = task_executor != NULL && _processing_is_mt;
+ if (mt && ParallelRefProcBalancingEnabled) {
+ balance_queues(refs_lists);
+ }
+ if (PrintReferenceGC && PrintGCDetails) {
+ size_t total = 0;
+ for (int i = 0; i < _num_q; ++i) {
+ total += refs_lists[i].length();
+ }
+ gclog_or_tty->print(", %u refs", total);
+ }
+
+ // 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) {
+ RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/);
+ task_executor->execute(phase1);
+ } else {
+ for (int i = 0; i < _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) {
+ RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/);
+ task_executor->execute(phase2);
+ } else {
+ for (int i = 0; i < _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) {
+ RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/);
+ task_executor->execute(phase3);
+ } else {
+ for (int i = 0; i < _num_q; i++) {
+ process_phase3(refs_lists[i], clear_referent,
+ is_alive, keep_alive, complete_gc);
+ }
+ }
+}
+
+void ReferenceProcessor::clean_up_discovered_references() {
+ // loop over the lists
+ for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
+ if (TraceReferenceGC && PrintGCDetails && ((i % _num_q) == 0)) {
+ gclog_or_tty->print_cr(
+ "\nScrubbing %s discovered list of Null referents",
+ list_name(i));
+ }
+ clean_up_discovered_reflist(_discoveredSoftRefs[i]);
+ }
+}
+
+void ReferenceProcessor::clean_up_discovered_reflist(DiscoveredList& refs_list) {
+ assert(!discovery_is_atomic(), "Else why call this method?");
+ DiscoveredListIterator iter(refs_list, NULL, NULL);
+ size_t length = refs_list.length();
+ while (iter.has_next()) {
+ iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
+ oop* next_addr = java_lang_ref_Reference::next_addr(iter.obj());
+ assert((*next_addr)->is_oop_or_null(), "bad next field");
+ // If referent has been cleared or Reference is not active,
+ // drop it.
+ if (iter.referent() == NULL || *next_addr != NULL) {
+ debug_only(
+ if (PrintGCDetails && TraceReferenceGC) {
+ gclog_or_tty->print_cr("clean_up_discovered_list: Dropping Reference: "
+ INTPTR_FORMAT " with next field: " INTPTR_FORMAT
+ " and referent: " INTPTR_FORMAT,
+ (address)iter.obj(), (address)*next_addr, (address)iter.referent());
+ }
+ )
+ // Remove Reference object from list
+ iter.remove();
+ --length;
+ } else {
+ iter.next();
+ }
+ }
+ refs_list.set_length(length);
+ NOT_PRODUCT(
+ if (PrintGCDetails && TraceReferenceGC) {
+ gclog_or_tty->print(
+ " Removed %d Refs with NULL referents out of %d discovered Refs",
+ iter.removed(), iter.processed());
+ }
+ )
+}
+
+inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) {
+ int 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();
+ assert(thr->is_GC_task_thread(),
+ "Dubious cast from Thread* to WorkerThread*?");
+ id = ((WorkerThread*)thr)->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 < _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();
+ }
+ return list;
+}
+
+inline void ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& list,
+ oop obj, oop* 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 retest = (oop)Atomic::cmpxchg_ptr(list.head(), 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.
+ list.set_head(obj);
+ list.set_length(list.length() + 1);
+ } 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 enqueued reference (" INTPTR_FORMAT ": %s)",
+ obj, obj->blueprint()->internal_name());
+ }
+ }
+}
+
+
+// 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 enqueued 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) {
+ // We enqueue references only if we are discovering refs
+ // (rather than processing discovered refs).
+ if (!_discovering_refs || !RegisterReferences) {
+ return false;
+ }
+ // We only enqueue active references.
+ oop* next_addr = java_lang_ref_Reference::next_addr(obj);
+ if (*next_addr != NULL) {
+ 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 enqueue references whose referents are not (yet) strongly
+ // reachable.
+ if (is_alive_non_header() != NULL) {
+ oop referent = java_lang_ref_Reference::referent(obj);
+ // We'd like to assert the following:
+ // assert(referent != NULL, "Refs with null referents already filtered");
+ // However, since this code may be executed concurrently with
+ // mutators, which can clear() the referent, it is not
+ // guaranteed that the referent is non-NULL.
+ if (is_alive_non_header()->do_object_b(referent)) {
+ return false; // referent is reachable
+ }
+ }
+
+ oop* discovered_addr = java_lang_ref_Reference::discovered_addr(obj);
+ assert(discovered_addr != NULL && (*discovered_addr)->is_oop_or_null(),
+ "bad discovered field");
+ if (*discovered_addr != NULL) {
+ // The reference has already been discovered...
+ if (TraceReferenceGC) {
+ gclog_or_tty->print_cr("Already enqueued reference (" INTPTR_FORMAT ": %s)",
+ (oopDesc*)obj, obj->blueprint()->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,
+ "Only possible with a concurrent collector");
+ return true;
+ }
+ }
+
+ if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
+ oop referent = java_lang_ref_Reference::referent(obj);
+ assert(referent->is_oop(), "bad referent");
+ // enqueue 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(referent))) {
+ // 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
+ }
+
+ // We do a raw store here, the field will be visited later when
+ // processing the discovered references.
+ if (_discovery_is_mt) {
+ add_to_discovered_list_mt(*list, obj, discovered_addr);
+ } else {
+ *discovered_addr = list->head();
+ list->set_head(obj);
+ list->set_length(list->length() + 1);
+ }
+
+ // In the MT discovery case, it is currently possible to see
+ // the following message multiple times if several threads
+ // discover a reference about the same time. Only one will
+ // however have actually added it to the disocvered queue.
+ // One could let add_to_discovered_list_mt() return an
+ // indication for success in queueing (by 1 thread) or
+ // failure (by all other threads), but I decided the extra
+ // code was not worth the effort for something that is
+ // only used for debugging support.
+ if (TraceReferenceGC) {
+ oop referent = java_lang_ref_Reference::referent(obj);
+ if (PrintGCDetails) {
+ gclog_or_tty->print_cr("Enqueued reference (" INTPTR_FORMAT ": %s)",
+ (oopDesc*) obj, obj->blueprint()->internal_name());
+ }
+ assert(referent->is_oop(), "Enqueued a bad referent");
+ }
+ assert(obj->is_oop(), "Enqueued a bad reference");
+ 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) {
+
+ NOT_PRODUCT(verify_ok_to_handle_reflists());
+
+ // Soft references
+ {
+ TraceTime tt("Preclean SoftReferences", PrintGCDetails && PrintReferenceGC,
+ false, gclog_or_tty);
+ for (int i = 0; i < _num_q; i++) {
+ preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive,
+ keep_alive, complete_gc, yield);
+ }
+ }
+ if (yield->should_return()) {
+ return;
+ }
+
+ // Weak references
+ {
+ TraceTime tt("Preclean WeakReferences", PrintGCDetails && PrintReferenceGC,
+ false, gclog_or_tty);
+ for (int i = 0; i < _num_q; i++) {
+ preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive,
+ keep_alive, complete_gc, yield);
+ }
+ }
+ if (yield->should_return()) {
+ return;
+ }
+
+ // Final references
+ {
+ TraceTime tt("Preclean FinalReferences", PrintGCDetails && PrintReferenceGC,
+ false, gclog_or_tty);
+ for (int i = 0; i < _num_q; i++) {
+ preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive,
+ keep_alive, complete_gc, yield);
+ }
+ }
+ if (yield->should_return()) {
+ return;
+ }
+
+ // Phantom references
+ {
+ TraceTime tt("Preclean PhantomReferences", PrintGCDetails && PrintReferenceGC,
+ false, gclog_or_tty);
+ for (int i = 0; i < _num_q; i++) {
+ 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: For this to work
+// correctly, refs discovery can not be happening concurrently with this
+// step.
+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);
+ size_t length = refs_list.length();
+ while (iter.has_next()) {
+ iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
+ oop* next_addr = java_lang_ref_Reference::next_addr(iter.obj());
+ if (iter.referent() == NULL || iter.is_referent_alive() ||
+ *next_addr != 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)",
+ iter.obj(), iter.obj()->blueprint()->internal_name());
+ }
+ // Remove Reference object from list
+ iter.remove();
+ --length;
+ // Keep alive its cohort.
+ iter.make_referent_alive();
+ keep_alive->do_oop(next_addr);
+ } else {
+ iter.next();
+ }
+ }
+ refs_list.set_length(length);
+
+ // Close the reachable set
+ complete_gc->do_void();
+
+ NOT_PRODUCT(
+ if (PrintGCDetails && PrintReferenceGC) {
+ gclog_or_tty->print(" Dropped %d Refs out of %d "
+ "Refs in discovered list ", iter.removed(), iter.processed());
+ }
+ )
+}
+
+const char* ReferenceProcessor::list_name(int i) {
+ assert(i >= 0 && i <= _num_q * subclasses_of_ref, "Out of bounds index");
+ int j = i / _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
+
+void ReferenceProcessor::verify() {
+ guarantee(_sentinelRef != NULL && _sentinelRef->is_oop(), "Lost _sentinelRef");
+}
+
+#ifndef PRODUCT
+void ReferenceProcessor::clear_discovered_references() {
+ guarantee(!_discovering_refs, "Discovering refs?");
+ for (int i = 0; i < _num_q * subclasses_of_ref; i++) {
+ oop obj = _discoveredSoftRefs[i].head();
+ while (obj != _sentinelRef) {
+ oop next = java_lang_ref_Reference::discovered(obj);
+ java_lang_ref_Reference::set_discovered(obj, (oop) NULL);
+ obj = next;
+ }
+ _discoveredSoftRefs[i].set_head(_sentinelRef);
+ _discoveredSoftRefs[i].set_length(0);
+ }
+}
+#endif // PRODUCT