duke@435: /* jmasa@2188: * Copyright (c) 2001, 2010, Oracle and/or its affiliates. All rights reserved. duke@435: * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. duke@435: * duke@435: * This code is free software; you can redistribute it and/or modify it duke@435: * under the terms of the GNU General Public License version 2 only, as duke@435: * published by the Free Software Foundation. duke@435: * duke@435: * This code is distributed in the hope that it will be useful, but WITHOUT duke@435: * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or duke@435: * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License duke@435: * version 2 for more details (a copy is included in the LICENSE file that duke@435: * accompanied this code). duke@435: * duke@435: * You should have received a copy of the GNU General Public License version duke@435: * 2 along with this work; if not, write to the Free Software Foundation, duke@435: * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. duke@435: * trims@1907: * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA trims@1907: * or visit www.oracle.com if you need additional information or have any trims@1907: * questions. duke@435: * duke@435: */ duke@435: stefank@2314: #include "precompiled.hpp" stefank@2314: #include "classfile/javaClasses.hpp" stefank@2314: #include "classfile/systemDictionary.hpp" stefank@2314: #include "gc_interface/collectedHeap.hpp" stefank@2314: #include "gc_interface/collectedHeap.inline.hpp" stefank@2314: #include "memory/referencePolicy.hpp" stefank@2314: #include "memory/referenceProcessor.hpp" stefank@2314: #include "oops/oop.inline.hpp" stefank@2314: #include "runtime/java.hpp" stefank@2314: #include "runtime/jniHandles.hpp" duke@435: ysr@888: ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL; ysr@888: ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = NULL; ysr@888: oop ReferenceProcessor::_sentinelRef = NULL; ysr@888: const int subclasses_of_ref = REF_PHANTOM - REF_OTHER; ysr@888: duke@435: // List of discovered references. duke@435: class DiscoveredList { duke@435: public: coleenp@548: DiscoveredList() : _len(0), _compressed_head(0), _oop_head(NULL) { } coleenp@548: oop head() const { coleenp@548: return UseCompressedOops ? oopDesc::decode_heap_oop_not_null(_compressed_head) : coleenp@548: _oop_head; coleenp@548: } coleenp@548: HeapWord* adr_head() { coleenp@548: return UseCompressedOops ? (HeapWord*)&_compressed_head : coleenp@548: (HeapWord*)&_oop_head; coleenp@548: } coleenp@548: void set_head(oop o) { coleenp@548: if (UseCompressedOops) { coleenp@548: // Must compress the head ptr. coleenp@548: _compressed_head = oopDesc::encode_heap_oop_not_null(o); coleenp@548: } else { coleenp@548: _oop_head = o; coleenp@548: } coleenp@548: } coleenp@548: bool empty() const { return head() == ReferenceProcessor::sentinel_ref(); } duke@435: size_t length() { return _len; } ysr@887: void set_length(size_t len) { _len = len; } ysr@887: void inc_length(size_t inc) { _len += inc; assert(_len > 0, "Error"); } ysr@887: void dec_length(size_t dec) { _len -= dec; } duke@435: private: coleenp@548: // Set value depending on UseCompressedOops. This could be a template class coleenp@548: // but then we have to fix all the instantiations and declarations that use this class. coleenp@548: oop _oop_head; coleenp@548: narrowOop _compressed_head; duke@435: size_t _len; duke@435: }; duke@435: duke@435: void referenceProcessor_init() { duke@435: ReferenceProcessor::init_statics(); duke@435: } duke@435: duke@435: void ReferenceProcessor::init_statics() { coleenp@548: assert(_sentinelRef == NULL, "should be initialized precisely once"); duke@435: EXCEPTION_MARK; duke@435: _sentinelRef = instanceKlass::cast( never@1577: SystemDictionary::Reference_klass())-> coleenp@548: allocate_permanent_instance(THREAD); duke@435: duke@435: // Initialize the master soft ref clock. duke@435: java_lang_ref_SoftReference::set_clock(os::javaTimeMillis()); duke@435: duke@435: if (HAS_PENDING_EXCEPTION) { duke@435: Handle ex(THREAD, PENDING_EXCEPTION); duke@435: vm_exit_during_initialization(ex); duke@435: } duke@435: assert(_sentinelRef != NULL && _sentinelRef->is_oop(), duke@435: "Just constructed it!"); ysr@888: _always_clear_soft_ref_policy = new AlwaysClearPolicy(); ysr@888: _default_soft_ref_policy = new COMPILER2_PRESENT(LRUMaxHeapPolicy()) ysr@888: NOT_COMPILER2(LRUCurrentHeapPolicy()); ysr@888: if (_always_clear_soft_ref_policy == NULL || _default_soft_ref_policy == NULL) { ysr@888: vm_exit_during_initialization("Could not allocate reference policy object"); ysr@888: } duke@435: guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery || duke@435: RefDiscoveryPolicy == ReferentBasedDiscovery, duke@435: "Unrecongnized RefDiscoveryPolicy"); duke@435: } duke@435: coleenp@548: ReferenceProcessor* coleenp@548: ReferenceProcessor::create_ref_processor(MemRegion span, coleenp@548: bool atomic_discovery, coleenp@548: bool mt_discovery, coleenp@548: BoolObjectClosure* is_alive_non_header, coleenp@548: int parallel_gc_threads, ysr@777: bool mt_processing, ysr@777: bool dl_needs_barrier) { duke@435: int mt_degree = 1; duke@435: if (parallel_gc_threads > 1) { duke@435: mt_degree = parallel_gc_threads; duke@435: } duke@435: ReferenceProcessor* rp = duke@435: new ReferenceProcessor(span, atomic_discovery, duke@435: mt_discovery, mt_degree, ysr@777: mt_processing && (parallel_gc_threads > 0), ysr@777: dl_needs_barrier); duke@435: if (rp == NULL) { duke@435: vm_exit_during_initialization("Could not allocate ReferenceProcessor object"); duke@435: } duke@435: rp->set_is_alive_non_header(is_alive_non_header); ysr@892: rp->setup_policy(false /* default soft ref policy */); duke@435: return rp; duke@435: } duke@435: duke@435: ReferenceProcessor::ReferenceProcessor(MemRegion span, coleenp@548: bool atomic_discovery, coleenp@548: bool mt_discovery, coleenp@548: int mt_degree, ysr@777: bool mt_processing, ysr@777: bool discovered_list_needs_barrier) : duke@435: _discovering_refs(false), duke@435: _enqueuing_is_done(false), duke@435: _is_alive_non_header(NULL), ysr@777: _discovered_list_needs_barrier(discovered_list_needs_barrier), ysr@777: _bs(NULL), duke@435: _processing_is_mt(mt_processing), duke@435: _next_id(0) duke@435: { duke@435: _span = span; duke@435: _discovery_is_atomic = atomic_discovery; duke@435: _discovery_is_mt = mt_discovery; duke@435: _num_q = mt_degree; jmasa@2188: _max_num_q = mt_degree; jmasa@2188: _discoveredSoftRefs = NEW_C_HEAP_ARRAY(DiscoveredList, _max_num_q * subclasses_of_ref); duke@435: if (_discoveredSoftRefs == NULL) { duke@435: vm_exit_during_initialization("Could not allocated RefProc Array"); duke@435: } jmasa@2188: _discoveredWeakRefs = &_discoveredSoftRefs[_max_num_q]; jmasa@2188: _discoveredFinalRefs = &_discoveredWeakRefs[_max_num_q]; jmasa@2188: _discoveredPhantomRefs = &_discoveredFinalRefs[_max_num_q]; coleenp@548: assert(sentinel_ref() != NULL, "_sentinelRef is NULL"); duke@435: // Initialized all entries to _sentinelRef jmasa@2188: for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) { coleenp@548: _discoveredSoftRefs[i].set_head(sentinel_ref()); duke@435: _discoveredSoftRefs[i].set_length(0); duke@435: } ysr@777: // If we do barreirs, cache a copy of the barrier set. ysr@777: if (discovered_list_needs_barrier) { ysr@777: _bs = Universe::heap()->barrier_set(); ysr@777: } duke@435: } duke@435: duke@435: #ifndef PRODUCT duke@435: void ReferenceProcessor::verify_no_references_recorded() { duke@435: guarantee(!_discovering_refs, "Discovering refs?"); jmasa@2188: for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) { duke@435: guarantee(_discoveredSoftRefs[i].empty(), duke@435: "Found non-empty discovered list"); duke@435: } duke@435: } duke@435: #endif duke@435: duke@435: void ReferenceProcessor::weak_oops_do(OopClosure* f) { jmasa@2188: // Should this instead be jmasa@2188: // for (int i = 0; i < subclasses_of_ref; i++_ { jmasa@2188: // for (int j = 0; j < _num_q; j++) { jmasa@2188: // int index = i * _max_num_q + j; jmasa@2188: for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) { coleenp@548: if (UseCompressedOops) { coleenp@548: f->do_oop((narrowOop*)_discoveredSoftRefs[i].adr_head()); coleenp@548: } else { coleenp@548: f->do_oop((oop*)_discoveredSoftRefs[i].adr_head()); coleenp@548: } duke@435: } duke@435: } duke@435: duke@435: void ReferenceProcessor::oops_do(OopClosure* f) { coleenp@548: f->do_oop(adr_sentinel_ref()); duke@435: } duke@435: coleenp@548: void ReferenceProcessor::update_soft_ref_master_clock() { duke@435: // Update (advance) the soft ref master clock field. This must be done duke@435: // after processing the soft ref list. duke@435: jlong now = os::javaTimeMillis(); duke@435: jlong clock = java_lang_ref_SoftReference::clock(); duke@435: NOT_PRODUCT( duke@435: if (now < clock) { duke@435: warning("time warp: %d to %d", clock, now); duke@435: } duke@435: ) duke@435: // In product mode, protect ourselves from system time being adjusted duke@435: // externally and going backward; see note in the implementation of duke@435: // GenCollectedHeap::time_since_last_gc() for the right way to fix duke@435: // this uniformly throughout the VM; see bug-id 4741166. XXX duke@435: if (now > clock) { duke@435: java_lang_ref_SoftReference::set_clock(now); duke@435: } duke@435: // Else leave clock stalled at its old value until time progresses duke@435: // past clock value. duke@435: } duke@435: coleenp@548: void ReferenceProcessor::process_discovered_references( duke@435: BoolObjectClosure* is_alive, duke@435: OopClosure* keep_alive, duke@435: VoidClosure* complete_gc, duke@435: AbstractRefProcTaskExecutor* task_executor) { duke@435: NOT_PRODUCT(verify_ok_to_handle_reflists()); duke@435: duke@435: assert(!enqueuing_is_done(), "If here enqueuing should not be complete"); duke@435: // Stop treating discovered references specially. duke@435: disable_discovery(); duke@435: duke@435: bool trace_time = PrintGCDetails && PrintReferenceGC; duke@435: // Soft references duke@435: { duke@435: TraceTime tt("SoftReference", trace_time, false, gclog_or_tty); ysr@888: process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true, duke@435: is_alive, keep_alive, complete_gc, task_executor); duke@435: } duke@435: duke@435: update_soft_ref_master_clock(); duke@435: duke@435: // Weak references duke@435: { duke@435: TraceTime tt("WeakReference", trace_time, false, gclog_or_tty); duke@435: process_discovered_reflist(_discoveredWeakRefs, NULL, true, duke@435: is_alive, keep_alive, complete_gc, task_executor); duke@435: } duke@435: duke@435: // Final references duke@435: { duke@435: TraceTime tt("FinalReference", trace_time, false, gclog_or_tty); duke@435: process_discovered_reflist(_discoveredFinalRefs, NULL, false, duke@435: is_alive, keep_alive, complete_gc, task_executor); duke@435: } duke@435: duke@435: // Phantom references duke@435: { duke@435: TraceTime tt("PhantomReference", trace_time, false, gclog_or_tty); duke@435: process_discovered_reflist(_discoveredPhantomRefs, NULL, false, duke@435: is_alive, keep_alive, complete_gc, task_executor); duke@435: } duke@435: duke@435: // Weak global JNI references. It would make more sense (semantically) to duke@435: // traverse these simultaneously with the regular weak references above, but duke@435: // that is not how the JDK1.2 specification is. See #4126360. Native code can duke@435: // thus use JNI weak references to circumvent the phantom references and duke@435: // resurrect a "post-mortem" object. duke@435: { duke@435: TraceTime tt("JNI Weak Reference", trace_time, false, gclog_or_tty); duke@435: if (task_executor != NULL) { duke@435: task_executor->set_single_threaded_mode(); duke@435: } duke@435: process_phaseJNI(is_alive, keep_alive, complete_gc); duke@435: } duke@435: } duke@435: duke@435: #ifndef PRODUCT duke@435: // Calculate the number of jni handles. coleenp@548: uint ReferenceProcessor::count_jni_refs() { duke@435: class AlwaysAliveClosure: public BoolObjectClosure { duke@435: public: coleenp@548: virtual bool do_object_b(oop obj) { return true; } coleenp@548: virtual void do_object(oop obj) { assert(false, "Don't call"); } duke@435: }; duke@435: duke@435: class CountHandleClosure: public OopClosure { duke@435: private: duke@435: int _count; duke@435: public: duke@435: CountHandleClosure(): _count(0) {} coleenp@548: void do_oop(oop* unused) { _count++; } coleenp@548: void do_oop(narrowOop* unused) { ShouldNotReachHere(); } duke@435: int count() { return _count; } duke@435: }; duke@435: CountHandleClosure global_handle_count; duke@435: AlwaysAliveClosure always_alive; duke@435: JNIHandles::weak_oops_do(&always_alive, &global_handle_count); duke@435: return global_handle_count.count(); duke@435: } duke@435: #endif duke@435: duke@435: void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive, duke@435: OopClosure* keep_alive, duke@435: VoidClosure* complete_gc) { duke@435: #ifndef PRODUCT duke@435: if (PrintGCDetails && PrintReferenceGC) { duke@435: unsigned int count = count_jni_refs(); duke@435: gclog_or_tty->print(", %u refs", count); duke@435: } duke@435: #endif duke@435: JNIHandles::weak_oops_do(is_alive, keep_alive); duke@435: // Finally remember to keep sentinel around coleenp@548: keep_alive->do_oop(adr_sentinel_ref()); duke@435: complete_gc->do_void(); duke@435: } duke@435: coleenp@548: coleenp@548: template phh@1558: bool enqueue_discovered_ref_helper(ReferenceProcessor* ref, phh@1558: AbstractRefProcTaskExecutor* task_executor) { coleenp@548: duke@435: // Remember old value of pending references list coleenp@548: T* pending_list_addr = (T*)java_lang_ref_Reference::pending_list_addr(); coleenp@548: T old_pending_list_value = *pending_list_addr; duke@435: duke@435: // Enqueue references that are not made active again, and duke@435: // clear the decks for the next collection (cycle). coleenp@548: ref->enqueue_discovered_reflists((HeapWord*)pending_list_addr, task_executor); duke@435: // Do the oop-check on pending_list_addr missed in duke@435: // enqueue_discovered_reflist. We should probably duke@435: // do a raw oop_check so that future such idempotent duke@435: // oop_stores relying on the oop-check side-effect duke@435: // may be elided automatically and safely without duke@435: // affecting correctness. coleenp@548: oop_store(pending_list_addr, oopDesc::load_decode_heap_oop(pending_list_addr)); duke@435: duke@435: // Stop treating discovered references specially. coleenp@548: ref->disable_discovery(); duke@435: duke@435: // Return true if new pending references were added duke@435: return old_pending_list_value != *pending_list_addr; duke@435: } duke@435: coleenp@548: bool ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor) { coleenp@548: NOT_PRODUCT(verify_ok_to_handle_reflists()); coleenp@548: if (UseCompressedOops) { coleenp@548: return enqueue_discovered_ref_helper(this, task_executor); coleenp@548: } else { coleenp@548: return enqueue_discovered_ref_helper(this, task_executor); coleenp@548: } coleenp@548: } coleenp@548: duke@435: void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list, coleenp@548: HeapWord* pending_list_addr) { duke@435: // Given a list of refs linked through the "discovered" field duke@435: // (java.lang.ref.Reference.discovered) chain them through the duke@435: // "next" field (java.lang.ref.Reference.next) and prepend duke@435: // to the pending list. duke@435: if (TraceReferenceGC && PrintGCDetails) { duke@435: gclog_or_tty->print_cr("ReferenceProcessor::enqueue_discovered_reflist list " duke@435: INTPTR_FORMAT, (address)refs_list.head()); duke@435: } duke@435: oop obj = refs_list.head(); duke@435: // Walk down the list, copying the discovered field into duke@435: // the next field and clearing it (except for the last duke@435: // non-sentinel object which is treated specially to avoid duke@435: // confusion with an active reference). coleenp@548: while (obj != sentinel_ref()) { duke@435: assert(obj->is_instanceRef(), "should be reference object"); duke@435: oop next = java_lang_ref_Reference::discovered(obj); duke@435: if (TraceReferenceGC && PrintGCDetails) { coleenp@548: gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next " INTPTR_FORMAT, coleenp@548: obj, next); duke@435: } coleenp@548: assert(java_lang_ref_Reference::next(obj) == NULL, coleenp@548: "The reference should not be enqueued"); coleenp@548: if (next == sentinel_ref()) { // obj is last duke@435: // Swap refs_list into pendling_list_addr and duke@435: // set obj's next to what we read from pending_list_addr. coleenp@548: oop old = oopDesc::atomic_exchange_oop(refs_list.head(), pending_list_addr); duke@435: // Need oop_check on pending_list_addr above; duke@435: // see special oop-check code at the end of duke@435: // enqueue_discovered_reflists() further below. duke@435: if (old == NULL) { duke@435: // obj should be made to point to itself, since duke@435: // pending list was empty. duke@435: java_lang_ref_Reference::set_next(obj, obj); duke@435: } else { duke@435: java_lang_ref_Reference::set_next(obj, old); duke@435: } duke@435: } else { duke@435: java_lang_ref_Reference::set_next(obj, next); duke@435: } duke@435: java_lang_ref_Reference::set_discovered(obj, (oop) NULL); duke@435: obj = next; duke@435: } duke@435: } duke@435: duke@435: // Parallel enqueue task duke@435: class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask { duke@435: public: duke@435: RefProcEnqueueTask(ReferenceProcessor& ref_processor, duke@435: DiscoveredList discovered_refs[], coleenp@548: HeapWord* pending_list_addr, duke@435: oop sentinel_ref, duke@435: int n_queues) duke@435: : EnqueueTask(ref_processor, discovered_refs, duke@435: pending_list_addr, sentinel_ref, n_queues) duke@435: { } duke@435: coleenp@548: virtual void work(unsigned int work_id) { duke@435: assert(work_id < (unsigned int)_ref_processor.num_q(), "Index out-of-bounds"); duke@435: // Simplest first cut: static partitioning. duke@435: int index = work_id; jmasa@2188: // The increment on "index" must correspond to the maximum number of queues jmasa@2188: // (n_queues) with which that ReferenceProcessor was created. That jmasa@2188: // is because of the "clever" way the discovered references lists were jmasa@2188: // allocated and are indexed into. That number is ParallelGCThreads jmasa@2188: // currently. Assert that. jmasa@2188: assert(_n_queues == (int) ParallelGCThreads, "Different number not expected"); jmasa@2188: for (int j = 0; jmasa@2188: j < subclasses_of_ref; jmasa@2188: j++, index += _n_queues) { duke@435: _ref_processor.enqueue_discovered_reflist( duke@435: _refs_lists[index], _pending_list_addr); duke@435: _refs_lists[index].set_head(_sentinel_ref); duke@435: _refs_lists[index].set_length(0); duke@435: } duke@435: } duke@435: }; duke@435: duke@435: // Enqueue references that are not made active again coleenp@548: void ReferenceProcessor::enqueue_discovered_reflists(HeapWord* pending_list_addr, duke@435: AbstractRefProcTaskExecutor* task_executor) { duke@435: if (_processing_is_mt && task_executor != NULL) { duke@435: // Parallel code duke@435: RefProcEnqueueTask tsk(*this, _discoveredSoftRefs, jmasa@2188: pending_list_addr, sentinel_ref(), _max_num_q); duke@435: task_executor->execute(tsk); duke@435: } else { duke@435: // Serial code: call the parent class's implementation jmasa@2188: for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) { duke@435: enqueue_discovered_reflist(_discoveredSoftRefs[i], pending_list_addr); coleenp@548: _discoveredSoftRefs[i].set_head(sentinel_ref()); duke@435: _discoveredSoftRefs[i].set_length(0); duke@435: } duke@435: } duke@435: } duke@435: duke@435: // Iterator for the list of discovered references. duke@435: class DiscoveredListIterator { duke@435: public: duke@435: inline DiscoveredListIterator(DiscoveredList& refs_list, duke@435: OopClosure* keep_alive, duke@435: BoolObjectClosure* is_alive); duke@435: duke@435: // End Of List. coleenp@548: inline bool has_next() const { return _next != ReferenceProcessor::sentinel_ref(); } duke@435: duke@435: // Get oop to the Reference object. coleenp@548: inline oop obj() const { return _ref; } duke@435: duke@435: // Get oop to the referent object. coleenp@548: inline oop referent() const { return _referent; } duke@435: duke@435: // Returns true if referent is alive. duke@435: inline bool is_referent_alive() const; duke@435: duke@435: // Loads data for the current reference. duke@435: // The "allow_null_referent" argument tells us to allow for the possibility duke@435: // of a NULL referent in the discovered Reference object. This typically duke@435: // happens in the case of concurrent collectors that may have done the ysr@887: // discovery concurrently, or interleaved, with mutator execution. duke@435: inline void load_ptrs(DEBUG_ONLY(bool allow_null_referent)); duke@435: duke@435: // Move to the next discovered reference. duke@435: inline void next(); duke@435: ysr@887: // Remove the current reference from the list duke@435: inline void remove(); duke@435: duke@435: // Make the Reference object active again. duke@435: inline void make_active() { java_lang_ref_Reference::set_next(_ref, NULL); } duke@435: duke@435: // Make the referent alive. coleenp@548: inline void make_referent_alive() { coleenp@548: if (UseCompressedOops) { coleenp@548: _keep_alive->do_oop((narrowOop*)_referent_addr); coleenp@548: } else { coleenp@548: _keep_alive->do_oop((oop*)_referent_addr); coleenp@548: } coleenp@548: } duke@435: duke@435: // Update the discovered field. coleenp@548: inline void update_discovered() { coleenp@548: // First _prev_next ref actually points into DiscoveredList (gross). coleenp@548: if (UseCompressedOops) { coleenp@548: _keep_alive->do_oop((narrowOop*)_prev_next); coleenp@548: } else { coleenp@548: _keep_alive->do_oop((oop*)_prev_next); coleenp@548: } coleenp@548: } duke@435: duke@435: // NULL out referent pointer. coleenp@548: inline void clear_referent() { oop_store_raw(_referent_addr, NULL); } duke@435: duke@435: // Statistics duke@435: NOT_PRODUCT( duke@435: inline size_t processed() const { return _processed; } duke@435: inline size_t removed() const { return _removed; } duke@435: ) duke@435: duke@435: inline void move_to_next(); duke@435: duke@435: private: duke@435: DiscoveredList& _refs_list; coleenp@548: HeapWord* _prev_next; duke@435: oop _ref; coleenp@548: HeapWord* _discovered_addr; duke@435: oop _next; coleenp@548: HeapWord* _referent_addr; duke@435: oop _referent; duke@435: OopClosure* _keep_alive; duke@435: BoolObjectClosure* _is_alive; duke@435: DEBUG_ONLY( duke@435: oop _first_seen; // cyclic linked list check duke@435: ) duke@435: NOT_PRODUCT( duke@435: size_t _processed; duke@435: size_t _removed; duke@435: ) duke@435: }; duke@435: duke@435: inline DiscoveredListIterator::DiscoveredListIterator(DiscoveredList& refs_list, duke@435: OopClosure* keep_alive, duke@435: BoolObjectClosure* is_alive) duke@435: : _refs_list(refs_list), coleenp@548: _prev_next(refs_list.adr_head()), duke@435: _ref(refs_list.head()), duke@435: #ifdef ASSERT duke@435: _first_seen(refs_list.head()), duke@435: #endif duke@435: #ifndef PRODUCT duke@435: _processed(0), duke@435: _removed(0), duke@435: #endif duke@435: _next(refs_list.head()), duke@435: _keep_alive(keep_alive), duke@435: _is_alive(is_alive) duke@435: { } duke@435: coleenp@548: inline bool DiscoveredListIterator::is_referent_alive() const { duke@435: return _is_alive->do_object_b(_referent); duke@435: } duke@435: coleenp@548: inline void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) { duke@435: _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref); coleenp@548: oop discovered = java_lang_ref_Reference::discovered(_ref); coleenp@548: assert(_discovered_addr && discovered->is_oop_or_null(), duke@435: "discovered field is bad"); coleenp@548: _next = discovered; duke@435: _referent_addr = java_lang_ref_Reference::referent_addr(_ref); coleenp@548: _referent = java_lang_ref_Reference::referent(_ref); duke@435: assert(Universe::heap()->is_in_reserved_or_null(_referent), duke@435: "Wrong oop found in java.lang.Reference object"); duke@435: assert(allow_null_referent ? duke@435: _referent->is_oop_or_null() duke@435: : _referent->is_oop(), duke@435: "bad referent"); duke@435: } duke@435: coleenp@548: inline void DiscoveredListIterator::next() { duke@435: _prev_next = _discovered_addr; duke@435: move_to_next(); duke@435: } duke@435: coleenp@548: inline void DiscoveredListIterator::remove() { duke@435: assert(_ref->is_oop(), "Dropping a bad reference"); coleenp@548: oop_store_raw(_discovered_addr, NULL); coleenp@548: // First _prev_next ref actually points into DiscoveredList (gross). coleenp@548: if (UseCompressedOops) { coleenp@548: // Remove Reference object from list. coleenp@548: oopDesc::encode_store_heap_oop_not_null((narrowOop*)_prev_next, _next); coleenp@548: } else { coleenp@548: // Remove Reference object from list. coleenp@548: oopDesc::store_heap_oop((oop*)_prev_next, _next); coleenp@548: } duke@435: NOT_PRODUCT(_removed++); ysr@887: _refs_list.dec_length(1); duke@435: } duke@435: coleenp@548: inline void DiscoveredListIterator::move_to_next() { duke@435: _ref = _next; duke@435: assert(_ref != _first_seen, "cyclic ref_list found"); duke@435: NOT_PRODUCT(_processed++); duke@435: } duke@435: duke@435: // NOTE: process_phase*() are largely similar, and at a high level duke@435: // merely iterate over the extant list applying a predicate to duke@435: // each of its elements and possibly removing that element from the duke@435: // list and applying some further closures to that element. duke@435: // We should consider the possibility of replacing these duke@435: // process_phase*() methods by abstracting them into duke@435: // a single general iterator invocation that receives appropriate duke@435: // closures that accomplish this work. duke@435: duke@435: // (SoftReferences only) Traverse the list and remove any SoftReferences whose duke@435: // referents are not alive, but that should be kept alive for policy reasons. duke@435: // Keep alive the transitive closure of all such referents. duke@435: void coleenp@548: ReferenceProcessor::process_phase1(DiscoveredList& refs_list, duke@435: ReferencePolicy* policy, duke@435: BoolObjectClosure* is_alive, duke@435: OopClosure* keep_alive, duke@435: VoidClosure* complete_gc) { duke@435: assert(policy != NULL, "Must have a non-NULL policy"); coleenp@548: DiscoveredListIterator iter(refs_list, keep_alive, is_alive); duke@435: // Decide which softly reachable refs should be kept alive. duke@435: while (iter.has_next()) { duke@435: iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */)); duke@435: bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive(); duke@435: if (referent_is_dead && !policy->should_clear_reference(iter.obj())) { duke@435: if (TraceReferenceGC) { duke@435: gclog_or_tty->print_cr("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy", coleenp@548: iter.obj(), iter.obj()->blueprint()->internal_name()); duke@435: } ysr@887: // Remove Reference object from list ysr@887: iter.remove(); duke@435: // Make the Reference object active again duke@435: iter.make_active(); duke@435: // keep the referent around duke@435: iter.make_referent_alive(); ysr@887: iter.move_to_next(); duke@435: } else { duke@435: iter.next(); duke@435: } duke@435: } duke@435: // Close the reachable set duke@435: complete_gc->do_void(); duke@435: NOT_PRODUCT( duke@435: if (PrintGCDetails && TraceReferenceGC) { jmasa@2188: gclog_or_tty->print_cr(" Dropped %d dead Refs out of %d " jmasa@2188: "discovered Refs by policy list " INTPTR_FORMAT, jmasa@2188: iter.removed(), iter.processed(), (address)refs_list.head()); duke@435: } duke@435: ) duke@435: } duke@435: duke@435: // Traverse the list and remove any Refs that are not active, or duke@435: // whose referents are either alive or NULL. duke@435: void coleenp@548: ReferenceProcessor::pp2_work(DiscoveredList& refs_list, duke@435: BoolObjectClosure* is_alive, coleenp@548: OopClosure* keep_alive) { duke@435: assert(discovery_is_atomic(), "Error"); coleenp@548: DiscoveredListIterator iter(refs_list, keep_alive, is_alive); duke@435: while (iter.has_next()) { duke@435: iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); coleenp@548: DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());) coleenp@548: assert(next == NULL, "Should not discover inactive Reference"); duke@435: if (iter.is_referent_alive()) { duke@435: if (TraceReferenceGC) { duke@435: gclog_or_tty->print_cr("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)", coleenp@548: iter.obj(), iter.obj()->blueprint()->internal_name()); duke@435: } duke@435: // The referent is reachable after all. ysr@887: // Remove Reference object from list. ysr@887: iter.remove(); duke@435: // Update the referent pointer as necessary: Note that this duke@435: // should not entail any recursive marking because the duke@435: // referent must already have been traversed. duke@435: iter.make_referent_alive(); ysr@887: iter.move_to_next(); duke@435: } else { duke@435: iter.next(); duke@435: } duke@435: } duke@435: NOT_PRODUCT( duke@435: if (PrintGCDetails && TraceReferenceGC) { jmasa@2188: gclog_or_tty->print_cr(" Dropped %d active Refs out of %d " jmasa@2188: "Refs in discovered list " INTPTR_FORMAT, jmasa@2188: iter.removed(), iter.processed(), (address)refs_list.head()); duke@435: } duke@435: ) duke@435: } duke@435: duke@435: void coleenp@548: ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList& refs_list, coleenp@548: BoolObjectClosure* is_alive, coleenp@548: OopClosure* keep_alive, coleenp@548: VoidClosure* complete_gc) { duke@435: assert(!discovery_is_atomic(), "Error"); coleenp@548: DiscoveredListIterator iter(refs_list, keep_alive, is_alive); duke@435: while (iter.has_next()) { duke@435: iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); coleenp@548: HeapWord* next_addr = java_lang_ref_Reference::next_addr(iter.obj()); coleenp@548: oop next = java_lang_ref_Reference::next(iter.obj()); duke@435: if ((iter.referent() == NULL || iter.is_referent_alive() || coleenp@548: next != NULL)) { coleenp@548: assert(next->is_oop_or_null(), "bad next field"); duke@435: // Remove Reference object from list duke@435: iter.remove(); duke@435: // Trace the cohorts duke@435: iter.make_referent_alive(); coleenp@548: if (UseCompressedOops) { coleenp@548: keep_alive->do_oop((narrowOop*)next_addr); coleenp@548: } else { coleenp@548: keep_alive->do_oop((oop*)next_addr); coleenp@548: } ysr@887: iter.move_to_next(); duke@435: } else { duke@435: iter.next(); duke@435: } duke@435: } duke@435: // Now close the newly reachable set duke@435: complete_gc->do_void(); duke@435: NOT_PRODUCT( duke@435: if (PrintGCDetails && TraceReferenceGC) { jmasa@2188: gclog_or_tty->print_cr(" Dropped %d active Refs out of %d " jmasa@2188: "Refs in discovered list " INTPTR_FORMAT, jmasa@2188: iter.removed(), iter.processed(), (address)refs_list.head()); duke@435: } duke@435: ) duke@435: } duke@435: duke@435: // Traverse the list and process the referents, by either coleenp@548: // clearing them or keeping them (and their reachable duke@435: // closure) alive. duke@435: void coleenp@548: ReferenceProcessor::process_phase3(DiscoveredList& refs_list, duke@435: bool clear_referent, duke@435: BoolObjectClosure* is_alive, duke@435: OopClosure* keep_alive, duke@435: VoidClosure* complete_gc) { jmasa@2188: ResourceMark rm; coleenp@548: DiscoveredListIterator iter(refs_list, keep_alive, is_alive); duke@435: while (iter.has_next()) { duke@435: iter.update_discovered(); duke@435: iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); duke@435: if (clear_referent) { duke@435: // NULL out referent pointer duke@435: iter.clear_referent(); duke@435: } else { duke@435: // keep the referent around duke@435: iter.make_referent_alive(); duke@435: } duke@435: if (TraceReferenceGC) { duke@435: gclog_or_tty->print_cr("Adding %sreference (" INTPTR_FORMAT ": %s) as pending", duke@435: clear_referent ? "cleared " : "", coleenp@548: iter.obj(), iter.obj()->blueprint()->internal_name()); duke@435: } duke@435: assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference"); duke@435: iter.next(); duke@435: } duke@435: // Remember to keep sentinel pointer around duke@435: iter.update_discovered(); duke@435: // Close the reachable set duke@435: complete_gc->do_void(); duke@435: } duke@435: duke@435: void coleenp@548: ReferenceProcessor::abandon_partial_discovered_list(DiscoveredList& refs_list) { coleenp@548: oop obj = refs_list.head(); coleenp@548: while (obj != sentinel_ref()) { coleenp@548: oop discovered = java_lang_ref_Reference::discovered(obj); coleenp@548: java_lang_ref_Reference::set_discovered_raw(obj, NULL); coleenp@548: obj = discovered; duke@435: } coleenp@548: refs_list.set_head(sentinel_ref()); coleenp@548: refs_list.set_length(0); duke@435: } duke@435: ysr@777: void ReferenceProcessor::abandon_partial_discovery() { ysr@777: // loop over the lists jmasa@2188: for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) { jmasa@2188: if (TraceReferenceGC && PrintGCDetails && ((i % _max_num_q) == 0)) { johnc@2316: gclog_or_tty->print_cr("\nAbandoning %s discovered list", johnc@2316: list_name(i)); ysr@777: } ysr@777: abandon_partial_discovered_list(_discoveredSoftRefs[i]); duke@435: } duke@435: } duke@435: duke@435: class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask { duke@435: public: duke@435: RefProcPhase1Task(ReferenceProcessor& ref_processor, duke@435: DiscoveredList refs_lists[], duke@435: ReferencePolicy* policy, duke@435: bool marks_oops_alive) duke@435: : ProcessTask(ref_processor, refs_lists, marks_oops_alive), duke@435: _policy(policy) duke@435: { } duke@435: virtual void work(unsigned int i, BoolObjectClosure& is_alive, duke@435: OopClosure& keep_alive, duke@435: VoidClosure& complete_gc) duke@435: { jmasa@2188: Thread* thr = Thread::current(); jmasa@2188: int refs_list_index = ((WorkerThread*)thr)->id(); jmasa@2188: _ref_processor.process_phase1(_refs_lists[refs_list_index], _policy, duke@435: &is_alive, &keep_alive, &complete_gc); duke@435: } duke@435: private: duke@435: ReferencePolicy* _policy; duke@435: }; duke@435: duke@435: class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask { duke@435: public: duke@435: RefProcPhase2Task(ReferenceProcessor& ref_processor, duke@435: DiscoveredList refs_lists[], duke@435: bool marks_oops_alive) duke@435: : ProcessTask(ref_processor, refs_lists, marks_oops_alive) duke@435: { } duke@435: virtual void work(unsigned int i, BoolObjectClosure& is_alive, duke@435: OopClosure& keep_alive, duke@435: VoidClosure& complete_gc) duke@435: { duke@435: _ref_processor.process_phase2(_refs_lists[i], duke@435: &is_alive, &keep_alive, &complete_gc); duke@435: } duke@435: }; duke@435: duke@435: class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask { duke@435: public: duke@435: RefProcPhase3Task(ReferenceProcessor& ref_processor, duke@435: DiscoveredList refs_lists[], duke@435: bool clear_referent, duke@435: bool marks_oops_alive) duke@435: : ProcessTask(ref_processor, refs_lists, marks_oops_alive), duke@435: _clear_referent(clear_referent) duke@435: { } duke@435: virtual void work(unsigned int i, BoolObjectClosure& is_alive, duke@435: OopClosure& keep_alive, duke@435: VoidClosure& complete_gc) duke@435: { jmasa@2188: // Don't use "refs_list_index" calculated in this way because jmasa@2188: // balance_queues() has moved the Ref's into the first n queues. jmasa@2188: // Thread* thr = Thread::current(); jmasa@2188: // int refs_list_index = ((WorkerThread*)thr)->id(); jmasa@2188: // _ref_processor.process_phase3(_refs_lists[refs_list_index], _clear_referent, duke@435: _ref_processor.process_phase3(_refs_lists[i], _clear_referent, duke@435: &is_alive, &keep_alive, &complete_gc); duke@435: } duke@435: private: duke@435: bool _clear_referent; duke@435: }; duke@435: duke@435: // Balances reference queues. jmasa@2188: // Move entries from all queues[0, 1, ..., _max_num_q-1] to jmasa@2188: // queues[0, 1, ..., _num_q-1] because only the first _num_q jmasa@2188: // corresponding to the active workers will be processed. duke@435: void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[]) duke@435: { duke@435: // calculate total length duke@435: size_t total_refs = 0; jmasa@2188: if (TraceReferenceGC && PrintGCDetails) { jmasa@2188: gclog_or_tty->print_cr("\nBalance ref_lists "); jmasa@2188: } jmasa@2188: jmasa@2188: for (int i = 0; i < _max_num_q; ++i) { duke@435: total_refs += ref_lists[i].length(); jmasa@2188: if (TraceReferenceGC && PrintGCDetails) { jmasa@2188: gclog_or_tty->print("%d ", ref_lists[i].length()); jmasa@2188: } jmasa@2188: } jmasa@2188: if (TraceReferenceGC && PrintGCDetails) { jmasa@2188: gclog_or_tty->print_cr(" = %d", total_refs); duke@435: } duke@435: size_t avg_refs = total_refs / _num_q + 1; duke@435: int to_idx = 0; jmasa@2188: for (int from_idx = 0; from_idx < _max_num_q; from_idx++) { jmasa@2188: bool move_all = false; jmasa@2188: if (from_idx >= _num_q) { jmasa@2188: move_all = ref_lists[from_idx].length() > 0; jmasa@2188: } jmasa@2188: while ((ref_lists[from_idx].length() > avg_refs) || jmasa@2188: move_all) { duke@435: assert(to_idx < _num_q, "Sanity Check!"); duke@435: if (ref_lists[to_idx].length() < avg_refs) { duke@435: // move superfluous refs jmasa@2188: size_t refs_to_move; jmasa@2188: // Move all the Ref's if the from queue will not be processed. jmasa@2188: if (move_all) { jmasa@2188: refs_to_move = MIN2(ref_lists[from_idx].length(), jmasa@2188: avg_refs - ref_lists[to_idx].length()); jmasa@2188: } else { jmasa@2188: refs_to_move = MIN2(ref_lists[from_idx].length() - avg_refs, jmasa@2188: avg_refs - ref_lists[to_idx].length()); jmasa@2188: } duke@435: oop move_head = ref_lists[from_idx].head(); duke@435: oop move_tail = move_head; duke@435: oop new_head = move_head; duke@435: // find an element to split the list on duke@435: for (size_t j = 0; j < refs_to_move; ++j) { duke@435: move_tail = new_head; coleenp@548: new_head = java_lang_ref_Reference::discovered(new_head); duke@435: } duke@435: java_lang_ref_Reference::set_discovered(move_tail, ref_lists[to_idx].head()); duke@435: ref_lists[to_idx].set_head(move_head); ysr@887: ref_lists[to_idx].inc_length(refs_to_move); duke@435: ref_lists[from_idx].set_head(new_head); ysr@887: ref_lists[from_idx].dec_length(refs_to_move); jmasa@2188: if (ref_lists[from_idx].length() == 0) { jmasa@2188: break; jmasa@2188: } duke@435: } else { jmasa@2188: to_idx = (to_idx + 1) % _num_q; duke@435: } duke@435: } duke@435: } jmasa@2188: #ifdef ASSERT jmasa@2188: size_t balanced_total_refs = 0; jmasa@2188: for (int i = 0; i < _max_num_q; ++i) { jmasa@2188: balanced_total_refs += ref_lists[i].length(); jmasa@2188: if (TraceReferenceGC && PrintGCDetails) { jmasa@2188: gclog_or_tty->print("%d ", ref_lists[i].length()); jmasa@2188: } jmasa@2188: } jmasa@2188: if (TraceReferenceGC && PrintGCDetails) { jmasa@2188: gclog_or_tty->print_cr(" = %d", balanced_total_refs); jmasa@2188: gclog_or_tty->flush(); jmasa@2188: } jmasa@2188: assert(total_refs == balanced_total_refs, "Balancing was incomplete"); jmasa@2188: #endif jmasa@2188: } jmasa@2188: jmasa@2188: void ReferenceProcessor::balance_all_queues() { jmasa@2188: balance_queues(_discoveredSoftRefs); jmasa@2188: balance_queues(_discoveredWeakRefs); jmasa@2188: balance_queues(_discoveredFinalRefs); jmasa@2188: balance_queues(_discoveredPhantomRefs); duke@435: } duke@435: duke@435: void duke@435: ReferenceProcessor::process_discovered_reflist( duke@435: DiscoveredList refs_lists[], duke@435: ReferencePolicy* policy, duke@435: bool clear_referent, duke@435: BoolObjectClosure* is_alive, duke@435: OopClosure* keep_alive, duke@435: VoidClosure* complete_gc, duke@435: AbstractRefProcTaskExecutor* task_executor) duke@435: { jmasa@2188: bool mt_processing = task_executor != NULL && _processing_is_mt; jmasa@2188: // If discovery used MT and a dynamic number of GC threads, then jmasa@2188: // the queues must be balanced for correctness if fewer than the jmasa@2188: // maximum number of queues were used. The number of queue used jmasa@2188: // during discovery may be different than the number to be used jmasa@2188: // for processing so don't depend of _num_q < _max_num_q as part jmasa@2188: // of the test. jmasa@2188: bool must_balance = _discovery_is_mt; jmasa@2188: jmasa@2188: if ((mt_processing && ParallelRefProcBalancingEnabled) || jmasa@2188: must_balance) { duke@435: balance_queues(refs_lists); duke@435: } duke@435: if (PrintReferenceGC && PrintGCDetails) { duke@435: size_t total = 0; duke@435: for (int i = 0; i < _num_q; ++i) { duke@435: total += refs_lists[i].length(); duke@435: } duke@435: gclog_or_tty->print(", %u refs", total); duke@435: } duke@435: duke@435: // Phase 1 (soft refs only): duke@435: // . Traverse the list and remove any SoftReferences whose duke@435: // referents are not alive, but that should be kept alive for duke@435: // policy reasons. Keep alive the transitive closure of all duke@435: // such referents. duke@435: if (policy != NULL) { jmasa@2188: if (mt_processing) { duke@435: RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/); duke@435: task_executor->execute(phase1); duke@435: } else { duke@435: for (int i = 0; i < _num_q; i++) { duke@435: process_phase1(refs_lists[i], policy, duke@435: is_alive, keep_alive, complete_gc); duke@435: } duke@435: } duke@435: } else { // policy == NULL duke@435: assert(refs_lists != _discoveredSoftRefs, duke@435: "Policy must be specified for soft references."); duke@435: } duke@435: duke@435: // Phase 2: duke@435: // . Traverse the list and remove any refs whose referents are alive. jmasa@2188: if (mt_processing) { duke@435: RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/); duke@435: task_executor->execute(phase2); duke@435: } else { duke@435: for (int i = 0; i < _num_q; i++) { duke@435: process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc); duke@435: } duke@435: } duke@435: duke@435: // Phase 3: duke@435: // . Traverse the list and process referents as appropriate. jmasa@2188: if (mt_processing) { duke@435: RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/); duke@435: task_executor->execute(phase3); duke@435: } else { duke@435: for (int i = 0; i < _num_q; i++) { duke@435: process_phase3(refs_lists[i], clear_referent, duke@435: is_alive, keep_alive, complete_gc); duke@435: } duke@435: } duke@435: } duke@435: duke@435: void ReferenceProcessor::clean_up_discovered_references() { duke@435: // loop over the lists jmasa@2188: // Should this instead be jmasa@2188: // for (int i = 0; i < subclasses_of_ref; i++_ { jmasa@2188: // for (int j = 0; j < _num_q; j++) { jmasa@2188: // int index = i * _max_num_q + j; jmasa@2188: for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) { duke@435: if (TraceReferenceGC && PrintGCDetails && ((i % _num_q) == 0)) { duke@435: gclog_or_tty->print_cr( duke@435: "\nScrubbing %s discovered list of Null referents", duke@435: list_name(i)); duke@435: } duke@435: clean_up_discovered_reflist(_discoveredSoftRefs[i]); duke@435: } duke@435: } duke@435: duke@435: void ReferenceProcessor::clean_up_discovered_reflist(DiscoveredList& refs_list) { duke@435: assert(!discovery_is_atomic(), "Else why call this method?"); duke@435: DiscoveredListIterator iter(refs_list, NULL, NULL); duke@435: while (iter.has_next()) { duke@435: iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); coleenp@548: oop next = java_lang_ref_Reference::next(iter.obj()); coleenp@548: assert(next->is_oop_or_null(), "bad next field"); duke@435: // If referent has been cleared or Reference is not active, duke@435: // drop it. coleenp@548: if (iter.referent() == NULL || next != NULL) { duke@435: debug_only( duke@435: if (PrintGCDetails && TraceReferenceGC) { duke@435: gclog_or_tty->print_cr("clean_up_discovered_list: Dropping Reference: " duke@435: INTPTR_FORMAT " with next field: " INTPTR_FORMAT duke@435: " and referent: " INTPTR_FORMAT, coleenp@548: iter.obj(), next, iter.referent()); duke@435: } duke@435: ) duke@435: // Remove Reference object from list duke@435: iter.remove(); ysr@887: iter.move_to_next(); duke@435: } else { duke@435: iter.next(); duke@435: } duke@435: } duke@435: NOT_PRODUCT( duke@435: if (PrintGCDetails && TraceReferenceGC) { duke@435: gclog_or_tty->print( duke@435: " Removed %d Refs with NULL referents out of %d discovered Refs", duke@435: iter.removed(), iter.processed()); duke@435: } duke@435: ) duke@435: } duke@435: duke@435: inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) { duke@435: int id = 0; duke@435: // Determine the queue index to use for this object. duke@435: if (_discovery_is_mt) { duke@435: // During a multi-threaded discovery phase, duke@435: // each thread saves to its "own" list. duke@435: Thread* thr = Thread::current(); johnc@2316: id = thr->as_Worker_thread()->id(); duke@435: } else { duke@435: // single-threaded discovery, we save in round-robin duke@435: // fashion to each of the lists. duke@435: if (_processing_is_mt) { duke@435: id = next_id(); duke@435: } duke@435: } jmasa@2188: assert(0 <= id && id < _max_num_q, "Id is out-of-bounds (call Freud?)"); duke@435: duke@435: // Get the discovered queue to which we will add duke@435: DiscoveredList* list = NULL; duke@435: switch (rt) { duke@435: case REF_OTHER: duke@435: // Unknown reference type, no special treatment duke@435: break; duke@435: case REF_SOFT: duke@435: list = &_discoveredSoftRefs[id]; duke@435: break; duke@435: case REF_WEAK: duke@435: list = &_discoveredWeakRefs[id]; duke@435: break; duke@435: case REF_FINAL: duke@435: list = &_discoveredFinalRefs[id]; duke@435: break; duke@435: case REF_PHANTOM: duke@435: list = &_discoveredPhantomRefs[id]; duke@435: break; duke@435: case REF_NONE: duke@435: // we should not reach here if we are an instanceRefKlass duke@435: default: duke@435: ShouldNotReachHere(); duke@435: } jmasa@2188: if (TraceReferenceGC && PrintGCDetails) { johnc@2316: gclog_or_tty->print_cr("Thread %d gets list " INTPTR_FORMAT, id, list); jmasa@2188: } duke@435: return list; duke@435: } duke@435: coleenp@548: inline void coleenp@548: ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list, coleenp@548: oop obj, coleenp@548: HeapWord* discovered_addr) { duke@435: assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller"); duke@435: // First we must make sure this object is only enqueued once. CAS in a non null duke@435: // discovered_addr. ysr@777: oop current_head = refs_list.head(); ysr@777: ysr@1280: // Note: In the case of G1, this specific pre-barrier is strictly ysr@777: // not necessary because the only case we are interested in ysr@1280: // here is when *discovered_addr is NULL (see the CAS further below), ysr@1280: // so this will expand to nothing. As a result, we have manually ysr@1280: // elided this out for G1, but left in the test for some future ysr@1280: // collector that might have need for a pre-barrier here. ysr@777: if (_discovered_list_needs_barrier && !UseG1GC) { ysr@1280: if (UseCompressedOops) { ysr@1280: _bs->write_ref_field_pre((narrowOop*)discovered_addr, current_head); ysr@1280: } else { ysr@1280: _bs->write_ref_field_pre((oop*)discovered_addr, current_head); ysr@1280: } ysr@1280: guarantee(false, "Need to check non-G1 collector"); ysr@777: } ysr@777: oop retest = oopDesc::atomic_compare_exchange_oop(current_head, discovered_addr, coleenp@548: NULL); duke@435: if (retest == NULL) { duke@435: // This thread just won the right to enqueue the object. duke@435: // We have separate lists for enqueueing so no synchronization duke@435: // is necessary. coleenp@548: refs_list.set_head(obj); ysr@887: refs_list.inc_length(1); ysr@777: if (_discovered_list_needs_barrier) { ysr@1280: _bs->write_ref_field((void*)discovered_addr, current_head); ysr@777: } johnc@2316: johnc@2316: if (TraceReferenceGC) { johnc@2316: gclog_or_tty->print_cr("Enqueued reference (mt) (" INTPTR_FORMAT ": %s)", johnc@2316: obj, obj->blueprint()->internal_name()); johnc@2316: } duke@435: } else { duke@435: // If retest was non NULL, another thread beat us to it: duke@435: // The reference has already been discovered... duke@435: if (TraceReferenceGC) { duke@435: gclog_or_tty->print_cr("Already enqueued reference (" INTPTR_FORMAT ": %s)", duke@435: obj, obj->blueprint()->internal_name()); duke@435: } duke@435: } duke@435: } duke@435: ysr@2337: #ifndef PRODUCT ysr@2337: // Non-atomic (i.e. concurrent) discovery might allow us ysr@2337: // to observe j.l.References with NULL referents, being those ysr@2337: // cleared concurrently by mutators during (or after) discovery. ysr@2337: void ReferenceProcessor::verify_referent(oop obj) { ysr@2337: bool da = discovery_is_atomic(); ysr@2337: oop referent = java_lang_ref_Reference::referent(obj); ysr@2337: assert(da ? referent->is_oop() : referent->is_oop_or_null(), ysr@2337: err_msg("Bad referent " INTPTR_FORMAT " found in Reference " ysr@2337: INTPTR_FORMAT " during %satomic discovery ", ysr@2337: (intptr_t)referent, (intptr_t)obj, da ? "" : "non-")); ysr@2337: } ysr@2337: #endif ysr@2337: duke@435: // We mention two of several possible choices here: duke@435: // #0: if the reference object is not in the "originating generation" duke@435: // (or part of the heap being collected, indicated by our "span" duke@435: // we don't treat it specially (i.e. we scan it as we would duke@435: // a normal oop, treating its references as strong references). duke@435: // This means that references can't be enqueued unless their duke@435: // referent is also in the same span. This is the simplest, duke@435: // most "local" and most conservative approach, albeit one duke@435: // that may cause weak references to be enqueued least promptly. duke@435: // We call this choice the "ReferenceBasedDiscovery" policy. duke@435: // #1: the reference object may be in any generation (span), but if duke@435: // the referent is in the generation (span) being currently collected duke@435: // then we can discover the reference object, provided duke@435: // the object has not already been discovered by duke@435: // a different concurrently running collector (as may be the duke@435: // case, for instance, if the reference object is in CMS and duke@435: // the referent in DefNewGeneration), and provided the processing duke@435: // of this reference object by the current collector will duke@435: // appear atomic to every other collector in the system. duke@435: // (Thus, for instance, a concurrent collector may not duke@435: // discover references in other generations even if the duke@435: // referent is in its own generation). This policy may, duke@435: // in certain cases, enqueue references somewhat sooner than duke@435: // might Policy #0 above, but at marginally increased cost duke@435: // and complexity in processing these references. duke@435: // We call this choice the "RefeferentBasedDiscovery" policy. duke@435: bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) { duke@435: // We enqueue references only if we are discovering refs duke@435: // (rather than processing discovered refs). duke@435: if (!_discovering_refs || !RegisterReferences) { duke@435: return false; duke@435: } duke@435: // We only enqueue active references. coleenp@548: oop next = java_lang_ref_Reference::next(obj); coleenp@548: if (next != NULL) { duke@435: return false; duke@435: } duke@435: duke@435: HeapWord* obj_addr = (HeapWord*)obj; duke@435: if (RefDiscoveryPolicy == ReferenceBasedDiscovery && duke@435: !_span.contains(obj_addr)) { duke@435: // Reference is not in the originating generation; duke@435: // don't treat it specially (i.e. we want to scan it as a normal duke@435: // object with strong references). duke@435: return false; duke@435: } duke@435: duke@435: // We only enqueue references whose referents are not (yet) strongly duke@435: // reachable. duke@435: if (is_alive_non_header() != NULL) { ysr@2337: verify_referent(obj); ysr@2337: if (is_alive_non_header()->do_object_b(java_lang_ref_Reference::referent(obj))) { duke@435: return false; // referent is reachable duke@435: } duke@435: } ysr@888: if (rt == REF_SOFT) { ysr@888: // For soft refs we can decide now if these are not ysr@888: // current candidates for clearing, in which case we ysr@888: // can mark through them now, rather than delaying that ysr@888: // to the reference-processing phase. Since all current ysr@888: // time-stamp policies advance the soft-ref clock only ysr@888: // at a major collection cycle, this is always currently ysr@888: // accurate. ysr@888: if (!_current_soft_ref_policy->should_clear_reference(obj)) { ysr@888: return false; ysr@888: } ysr@888: } duke@435: ysr@777: HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr(obj); ysr@777: const oop discovered = java_lang_ref_Reference::discovered(obj); coleenp@548: assert(discovered->is_oop_or_null(), "bad discovered field"); coleenp@548: if (discovered != NULL) { duke@435: // The reference has already been discovered... duke@435: if (TraceReferenceGC) { duke@435: gclog_or_tty->print_cr("Already enqueued reference (" INTPTR_FORMAT ": %s)", coleenp@548: obj, obj->blueprint()->internal_name()); duke@435: } duke@435: if (RefDiscoveryPolicy == ReferentBasedDiscovery) { duke@435: // assumes that an object is not processed twice; duke@435: // if it's been already discovered it must be on another duke@435: // generation's discovered list; so we won't discover it. duke@435: return false; duke@435: } else { duke@435: assert(RefDiscoveryPolicy == ReferenceBasedDiscovery, duke@435: "Unrecognized policy"); duke@435: // Check assumption that an object is not potentially duke@435: // discovered twice except by concurrent collectors that potentially duke@435: // trace the same Reference object twice. johnc@2316: assert(UseConcMarkSweepGC || UseG1GC, johnc@2316: "Only possible with a concurrent marking collector"); duke@435: return true; duke@435: } duke@435: } duke@435: duke@435: if (RefDiscoveryPolicy == ReferentBasedDiscovery) { ysr@2337: verify_referent(obj); duke@435: // enqueue if and only if either: duke@435: // reference is in our span or duke@435: // we are an atomic collector and referent is in our span duke@435: if (_span.contains(obj_addr) || ysr@2337: (discovery_is_atomic() && ysr@2337: _span.contains(java_lang_ref_Reference::referent(obj)))) { duke@435: // should_enqueue = true; duke@435: } else { duke@435: return false; duke@435: } duke@435: } else { duke@435: assert(RefDiscoveryPolicy == ReferenceBasedDiscovery && duke@435: _span.contains(obj_addr), "code inconsistency"); duke@435: } duke@435: duke@435: // Get the right type of discovered queue head. duke@435: DiscoveredList* list = get_discovered_list(rt); duke@435: if (list == NULL) { duke@435: return false; // nothing special needs to be done duke@435: } duke@435: duke@435: if (_discovery_is_mt) { duke@435: add_to_discovered_list_mt(*list, obj, discovered_addr); duke@435: } else { ysr@777: // If "_discovered_list_needs_barrier", we do write barriers when ysr@777: // updating the discovered reference list. Otherwise, we do a raw store ysr@777: // here: the field will be visited later when processing the discovered ysr@777: // references. ysr@777: oop current_head = list->head(); ysr@777: // As in the case further above, since we are over-writing a NULL ysr@777: // pre-value, we can safely elide the pre-barrier here for the case of G1. ysr@777: assert(discovered == NULL, "control point invariant"); ysr@777: if (_discovered_list_needs_barrier && !UseG1GC) { // safe to elide for G1 ysr@1280: if (UseCompressedOops) { ysr@1280: _bs->write_ref_field_pre((narrowOop*)discovered_addr, current_head); ysr@1280: } else { ysr@1280: _bs->write_ref_field_pre((oop*)discovered_addr, current_head); ysr@1280: } ysr@1280: guarantee(false, "Need to check non-G1 collector"); ysr@777: } ysr@777: oop_store_raw(discovered_addr, current_head); ysr@777: if (_discovered_list_needs_barrier) { ysr@1280: _bs->write_ref_field((void*)discovered_addr, current_head); ysr@777: } duke@435: list->set_head(obj); ysr@887: list->inc_length(1); duke@435: johnc@2316: if (TraceReferenceGC) { duke@435: gclog_or_tty->print_cr("Enqueued reference (" INTPTR_FORMAT ": %s)", johnc@2316: obj, obj->blueprint()->internal_name()); duke@435: } duke@435: } duke@435: assert(obj->is_oop(), "Enqueued a bad reference"); ysr@2337: verify_referent(obj); duke@435: return true; duke@435: } duke@435: duke@435: // Preclean the discovered references by removing those duke@435: // whose referents are alive, and by marking from those that duke@435: // are not active. These lists can be handled here duke@435: // in any order and, indeed, concurrently. duke@435: void ReferenceProcessor::preclean_discovered_references( duke@435: BoolObjectClosure* is_alive, duke@435: OopClosure* keep_alive, duke@435: VoidClosure* complete_gc, jmasa@1625: YieldClosure* yield, jmasa@1625: bool should_unload_classes) { duke@435: duke@435: NOT_PRODUCT(verify_ok_to_handle_reflists()); duke@435: jmasa@1370: #ifdef ASSERT jmasa@1370: bool must_remember_klasses = ClassUnloading && !UseConcMarkSweepGC || jmasa@1625: CMSClassUnloadingEnabled && UseConcMarkSweepGC || jmasa@1625: ExplicitGCInvokesConcurrentAndUnloadsClasses && jmasa@1625: UseConcMarkSweepGC && should_unload_classes; jmasa@1370: RememberKlassesChecker mx(must_remember_klasses); jmasa@1370: #endif duke@435: // Soft references duke@435: { duke@435: TraceTime tt("Preclean SoftReferences", PrintGCDetails && PrintReferenceGC, duke@435: false, gclog_or_tty); jmasa@2188: for (int i = 0; i < _max_num_q; i++) { ysr@887: if (yield->should_return()) { ysr@887: return; ysr@887: } duke@435: preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive, duke@435: keep_alive, complete_gc, yield); duke@435: } duke@435: } duke@435: duke@435: // Weak references duke@435: { duke@435: TraceTime tt("Preclean WeakReferences", PrintGCDetails && PrintReferenceGC, duke@435: false, gclog_or_tty); duke@435: for (int i = 0; i < _num_q; i++) { ysr@887: if (yield->should_return()) { ysr@887: return; ysr@887: } duke@435: preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive, duke@435: keep_alive, complete_gc, yield); duke@435: } duke@435: } duke@435: duke@435: // Final references duke@435: { duke@435: TraceTime tt("Preclean FinalReferences", PrintGCDetails && PrintReferenceGC, duke@435: false, gclog_or_tty); duke@435: for (int i = 0; i < _num_q; i++) { ysr@887: if (yield->should_return()) { ysr@887: return; ysr@887: } duke@435: preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive, duke@435: keep_alive, complete_gc, yield); duke@435: } duke@435: } duke@435: duke@435: // Phantom references duke@435: { duke@435: TraceTime tt("Preclean PhantomReferences", PrintGCDetails && PrintReferenceGC, duke@435: false, gclog_or_tty); duke@435: for (int i = 0; i < _num_q; i++) { ysr@887: if (yield->should_return()) { ysr@887: return; ysr@887: } duke@435: preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive, duke@435: keep_alive, complete_gc, yield); duke@435: } duke@435: } duke@435: } duke@435: duke@435: // Walk the given discovered ref list, and remove all reference objects duke@435: // whose referents are still alive, whose referents are NULL or which ysr@887: // are not active (have a non-NULL next field). NOTE: When we are ysr@887: // thus precleaning the ref lists (which happens single-threaded today), ysr@887: // we do not disable refs discovery to honour the correct semantics of ysr@887: // java.lang.Reference. As a result, we need to be careful below ysr@887: // that ref removal steps interleave safely with ref discovery steps ysr@887: // (in this thread). coleenp@548: void coleenp@548: ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list, coleenp@548: BoolObjectClosure* is_alive, coleenp@548: OopClosure* keep_alive, coleenp@548: VoidClosure* complete_gc, coleenp@548: YieldClosure* yield) { duke@435: DiscoveredListIterator iter(refs_list, keep_alive, is_alive); duke@435: while (iter.has_next()) { duke@435: iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); coleenp@548: oop obj = iter.obj(); coleenp@548: oop next = java_lang_ref_Reference::next(obj); duke@435: if (iter.referent() == NULL || iter.is_referent_alive() || coleenp@548: next != NULL) { duke@435: // The referent has been cleared, or is alive, or the Reference is not duke@435: // active; we need to trace and mark its cohort. duke@435: if (TraceReferenceGC) { duke@435: gclog_or_tty->print_cr("Precleaning Reference (" INTPTR_FORMAT ": %s)", duke@435: iter.obj(), iter.obj()->blueprint()->internal_name()); duke@435: } duke@435: // Remove Reference object from list duke@435: iter.remove(); duke@435: // Keep alive its cohort. duke@435: iter.make_referent_alive(); coleenp@548: if (UseCompressedOops) { coleenp@548: narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr(obj); coleenp@548: keep_alive->do_oop(next_addr); coleenp@548: } else { coleenp@548: oop* next_addr = (oop*)java_lang_ref_Reference::next_addr(obj); coleenp@548: keep_alive->do_oop(next_addr); coleenp@548: } ysr@887: iter.move_to_next(); duke@435: } else { duke@435: iter.next(); duke@435: } duke@435: } duke@435: // Close the reachable set duke@435: complete_gc->do_void(); duke@435: duke@435: NOT_PRODUCT( duke@435: if (PrintGCDetails && PrintReferenceGC) { jmasa@2188: gclog_or_tty->print_cr(" Dropped %d Refs out of %d " jmasa@2188: "Refs in discovered list " INTPTR_FORMAT, jmasa@2188: iter.removed(), iter.processed(), (address)refs_list.head()); duke@435: } duke@435: ) duke@435: } duke@435: duke@435: const char* ReferenceProcessor::list_name(int i) { jmasa@2188: assert(i >= 0 && i <= _max_num_q * subclasses_of_ref, "Out of bounds index"); jmasa@2188: int j = i / _max_num_q; duke@435: switch (j) { duke@435: case 0: return "SoftRef"; duke@435: case 1: return "WeakRef"; duke@435: case 2: return "FinalRef"; duke@435: case 3: return "PhantomRef"; duke@435: } duke@435: ShouldNotReachHere(); duke@435: return NULL; duke@435: } duke@435: duke@435: #ifndef PRODUCT duke@435: void ReferenceProcessor::verify_ok_to_handle_reflists() { duke@435: // empty for now duke@435: } duke@435: #endif duke@435: duke@435: void ReferenceProcessor::verify() { coleenp@548: guarantee(sentinel_ref() != NULL && sentinel_ref()->is_oop(), "Lost _sentinelRef"); duke@435: } duke@435: duke@435: #ifndef PRODUCT duke@435: void ReferenceProcessor::clear_discovered_references() { duke@435: guarantee(!_discovering_refs, "Discovering refs?"); jmasa@2188: for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) { duke@435: oop obj = _discoveredSoftRefs[i].head(); coleenp@548: while (obj != sentinel_ref()) { duke@435: oop next = java_lang_ref_Reference::discovered(obj); duke@435: java_lang_ref_Reference::set_discovered(obj, (oop) NULL); duke@435: obj = next; duke@435: } coleenp@548: _discoveredSoftRefs[i].set_head(sentinel_ref()); duke@435: _discoveredSoftRefs[i].set_length(0); duke@435: } duke@435: } duke@435: #endif // PRODUCT