/* * Copyright (c) 2001, 2025, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. * */ #include "classfile/javaClasses.inline.hpp" #include "compiler/compilerDefinitions.inline.hpp" #include "gc/shared/collectedHeap.hpp" #include "gc/shared/collectedHeap.inline.hpp" #include "gc/shared/gc_globals.hpp" #include "gc/shared/gcTimer.hpp" #include "gc/shared/gcTraceTime.inline.hpp" #include "gc/shared/referencePolicy.hpp" #include "gc/shared/referenceProcessor.inline.hpp" #include "gc/shared/referenceProcessorPhaseTimes.hpp" #include "logging/log.hpp" #include "memory/allocation.inline.hpp" #include "memory/resourceArea.hpp" #include "memory/universe.hpp" #include "oops/access.inline.hpp" #include "oops/oop.inline.hpp" #include "runtime/java.hpp" #include "runtime/nonJavaThread.hpp" #include "utilities/globalDefinitions.hpp" ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = nullptr; ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = nullptr; jlong ReferenceProcessor::_soft_ref_timestamp_clock = 0; void referenceProcessor_init() { ReferenceProcessor::init_statics(); } void ReferenceProcessor::init_statics() { // We need a monotonically non-decreasing time in ms but // os::javaTimeMillis() does not guarantee monotonicity. jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; // Initialize the soft ref timestamp clock. _soft_ref_timestamp_clock = now; // Also update the soft ref clock in j.l.r.SoftReference java_lang_ref_SoftReference::set_clock(_soft_ref_timestamp_clock); _always_clear_soft_ref_policy = new AlwaysClearPolicy(); if (CompilerConfig::is_c2_or_jvmci_compiler_enabled()) { _default_soft_ref_policy = new LRUMaxHeapPolicy(); } else { _default_soft_ref_policy = new LRUCurrentHeapPolicy(); } } void ReferenceProcessor::enable_discovery() { #ifdef ASSERT // Verify that we're not currently discovering refs assert(!_discovering_refs, "nested call?"); // Verify that the discovered lists are empty verify_no_references_recorded(); #endif // ASSERT _discovering_refs = true; } ReferenceProcessor::ReferenceProcessor(BoolObjectClosure* is_subject_to_discovery, uint mt_processing_degree, uint mt_discovery_degree, bool concurrent_discovery, BoolObjectClosure* is_alive_non_header) : _is_subject_to_discovery(is_subject_to_discovery), _discovering_refs(false), _next_id(0), _is_alive_non_header(is_alive_non_header) { assert(is_subject_to_discovery != nullptr, "must be set"); _discovery_is_concurrent = concurrent_discovery; _discovery_is_mt = (mt_discovery_degree > 1); _num_queues = MAX2(1U, mt_processing_degree); _max_num_queues = MAX2(_num_queues, mt_discovery_degree); _discovered_refs = NEW_C_HEAP_ARRAY(DiscoveredList, _max_num_queues * number_of_subclasses_of_ref(), mtGC); _discoveredSoftRefs = &_discovered_refs[0]; _discoveredWeakRefs = &_discoveredSoftRefs[_max_num_queues]; _discoveredFinalRefs = &_discoveredWeakRefs[_max_num_queues]; _discoveredPhantomRefs = &_discoveredFinalRefs[_max_num_queues]; // Initialize all entries to null for (uint i = 0; i < _max_num_queues * number_of_subclasses_of_ref(); i++) { _discovered_refs[i].clear(); } setup_policy(false /* default soft ref policy */); } #ifndef PRODUCT void ReferenceProcessor::verify_no_references_recorded() { guarantee(!_discovering_refs, "Discovering refs?"); for (uint i = 0; i < _max_num_queues * number_of_subclasses_of_ref(); i++) { guarantee(_discovered_refs[i].is_empty(), "Found non-empty discovered list at %u", i); } } #endif bool ReferenceProcessor::processing_is_mt() const { return ParallelRefProcEnabled && _num_queues > 1; } void ReferenceProcessor::weak_oops_do(OopClosure* f) { for (uint i = 0; i < _max_num_queues * number_of_subclasses_of_ref(); i++) { if (UseCompressedOops) { f->do_oop((narrowOop*)_discovered_refs[i].adr_head()); } else { f->do_oop((oop*)_discovered_refs[i].adr_head()); } } } void ReferenceProcessor::update_soft_ref_master_clock() { // Update (advance) the soft ref master clock field. This must be done // after processing the soft ref list. // We need a monotonically non-decreasing time in ms but // os::javaTimeMillis() does not guarantee monotonicity. jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; NOT_PRODUCT( if (now < _soft_ref_timestamp_clock) { log_warning(gc)("time warp: " JLONG_FORMAT " to " JLONG_FORMAT, _soft_ref_timestamp_clock, now); } ) // The values of now and _soft_ref_timestamp_clock are set using // javaTimeNanos(), which is guaranteed to be monotonically // non-decreasing provided the underlying platform provides such // a time source (and it is bug free). // In product mode, however, protect ourselves from non-monotonicity. if (now > _soft_ref_timestamp_clock) { _soft_ref_timestamp_clock = now; java_lang_ref_SoftReference::set_clock(now); } // Else leave clock stalled at its old value until time progresses // past clock value. } size_t ReferenceProcessor::total_count(DiscoveredList lists[]) const { size_t total = 0; for (uint i = 0; i < _max_num_queues; ++i) { total += lists[i].length(); } return total; } #ifdef ASSERT void ReferenceProcessor::verify_total_count_zero(DiscoveredList lists[], const char* type) { size_t count = total_count(lists); assert(count == 0, "%ss must be empty but has %zu elements", type, count); } #endif ReferenceProcessorStats ReferenceProcessor::process_discovered_references(RefProcProxyTask& proxy_task, ReferenceProcessorPhaseTimes& phase_times) { double start_time = os::elapsedTime(); // Stop treating discovered references specially. disable_discovery(); phase_times.set_ref_discovered(REF_SOFT, total_count(_discoveredSoftRefs)); phase_times.set_ref_discovered(REF_WEAK, total_count(_discoveredWeakRefs)); phase_times.set_ref_discovered(REF_FINAL, total_count(_discoveredFinalRefs)); phase_times.set_ref_discovered(REF_PHANTOM, total_count(_discoveredPhantomRefs)); update_soft_ref_master_clock(); phase_times.set_processing_is_mt(processing_is_mt()); { RefProcTotalPhaseTimesTracker tt(SoftWeakFinalRefsPhase, &phase_times); process_soft_weak_final_refs(proxy_task, phase_times); } { RefProcTotalPhaseTimesTracker tt(KeepAliveFinalRefsPhase, &phase_times); process_final_keep_alive(proxy_task, phase_times); } { RefProcTotalPhaseTimesTracker tt(PhantomRefsPhase, &phase_times); process_phantom_refs(proxy_task, phase_times); } phase_times.set_total_time_ms((os::elapsedTime() - start_time) * 1000); // Elements on discovered lists were pushed to the pending list. verify_no_references_recorded(); ReferenceProcessorStats stats(phase_times.ref_discovered(REF_SOFT), phase_times.ref_discovered(REF_WEAK), phase_times.ref_discovered(REF_FINAL), phase_times.ref_discovered(REF_PHANTOM)); return stats; } void BarrierEnqueueDiscoveredFieldClosure::enqueue(HeapWord* discovered_field_addr, oop value) { assert(Universe::heap()->is_in(discovered_field_addr), PTR_FORMAT " not in heap", p2i(discovered_field_addr)); HeapAccess::oop_store(discovered_field_addr, value); } void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) { _current_discovered_addr = java_lang_ref_Reference::discovered_addr_raw(_current_discovered); oop discovered = java_lang_ref_Reference::discovered(_current_discovered); assert(_current_discovered_addr && oopDesc::is_oop_or_null(discovered), "Expected an oop or null for discovered field at " PTR_FORMAT, p2i(discovered)); _next_discovered = discovered; _referent = java_lang_ref_Reference::unknown_referent_no_keepalive(_current_discovered); assert(Universe::heap()->is_in_or_null(_referent), "Wrong oop found in java.lang.Reference object"); assert(allow_null_referent ? oopDesc::is_oop_or_null(_referent) : oopDesc::is_oop(_referent), "Expected an oop%s for referent field at " PTR_FORMAT, (allow_null_referent ? " or null" : ""), p2i(_referent)); } void DiscoveredListIterator::remove() { assert(oopDesc::is_oop(_current_discovered), "Dropping a bad reference"); RawAccess<>::oop_store(_current_discovered_addr, oop(nullptr)); // First _prev_next ref actually points into DiscoveredList (gross). oop new_next; if (_next_discovered == _current_discovered) { // At the end of the list, we should make _prev point to itself. // If _ref is the first ref, then _prev_next will be in the DiscoveredList, // and _prev will be null. new_next = _prev_discovered; } else { new_next = _next_discovered; } // Remove Reference object from discovered list. We do not need barriers here, // as we only remove. We will do the barrier when we actually advance the cursor. RawAccess<>::oop_store(_prev_discovered_addr, new_next); _removed++; _refs_list.dec_length(1); } void DiscoveredListIterator::make_referent_alive() { HeapWord* addr = java_lang_ref_Reference::referent_addr_raw(_current_discovered); if (UseCompressedOops) { _keep_alive->do_oop((narrowOop*)addr); } else { _keep_alive->do_oop((oop*)addr); } } void DiscoveredListIterator::clear_referent() { java_lang_ref_Reference::clear_referent_raw(_current_discovered); } void DiscoveredListIterator::enqueue() { if (_prev_discovered_addr != _refs_list.adr_head()) { _enqueue->enqueue(_prev_discovered_addr, _current_discovered); } else { RawAccess<>::oop_store(_prev_discovered_addr, _current_discovered); } } void DiscoveredListIterator::complete_enqueue() { if (_prev_discovered != nullptr) { // This is the last object. // Swap refs_list into pending list and set obj's // discovered to what we read from the pending list. oop old = Universe::swap_reference_pending_list(_refs_list.head()); _enqueue->enqueue(java_lang_ref_Reference::discovered_addr_raw(_prev_discovered), old); } } inline void log_preclean_ref(const DiscoveredListIterator& iter, const char* reason) { if (log_develop_is_enabled(Trace, gc, ref)) { ResourceMark rm; log_develop_trace(gc, ref)("Precleaning %s reference " PTR_FORMAT ": %s", reason, p2i(iter.obj()), iter.obj()->klass()->internal_name()); } } inline void log_dropped_ref(const DiscoveredListIterator& iter, const char* reason) { if (log_develop_is_enabled(Trace, gc, ref)) { ResourceMark rm; log_develop_trace(gc, ref)("Dropping %s reference " PTR_FORMAT ": %s", reason, p2i(iter.obj()), iter.obj()->klass()->internal_name()); } } inline void log_enqueued_ref(const DiscoveredListIterator& iter, const char* reason) { if (log_develop_is_enabled(Trace, gc, ref)) { ResourceMark rm; log_develop_trace(gc, ref)("Enqueue %s reference (" PTR_FORMAT ": %s)", reason, p2i(iter.obj()), iter.obj()->klass()->internal_name()); } assert(oopDesc::is_oop(iter.obj()), "Adding a bad reference"); } size_t ReferenceProcessor::process_discovered_list_work(DiscoveredList& refs_list, BoolObjectClosure* is_alive, OopClosure* keep_alive, EnqueueDiscoveredFieldClosure* enqueue, bool do_enqueue_and_clear) { DiscoveredListIterator iter(refs_list, keep_alive, is_alive, enqueue); while (iter.has_next()) { iter.load_ptrs(DEBUG_ONLY(discovery_is_concurrent() /* allow_null_referent */)); if (iter.referent() == nullptr) { // Reference has been cleared since discovery; only possible if // discovery is concurrent (checked by load_ptrs). Remove // reference from list. log_dropped_ref(iter, "cleared"); iter.remove(); iter.move_to_next(); } else if (iter.is_referent_alive()) { // The referent is reachable after all. // Remove reference from list. log_dropped_ref(iter, "reachable"); iter.remove(); // Update the referent pointer as necessary. Note that this // should not entail any recursive marking because the // referent must already have been traversed. iter.make_referent_alive(); iter.move_to_next(); } else { if (do_enqueue_and_clear) { iter.clear_referent(); iter.enqueue(); log_enqueued_ref(iter, "cleared"); } // Keep in discovered list iter.next(); } } if (do_enqueue_and_clear) { iter.complete_enqueue(); refs_list.clear(); } log_develop_trace(gc, ref)(" Dropped %zu active Refs out of %zu" " Refs in discovered list " PTR_FORMAT, iter.removed(), iter.processed(), p2i(&refs_list)); return iter.removed(); } size_t ReferenceProcessor::process_final_keep_alive_work(DiscoveredList& refs_list, OopClosure* keep_alive, EnqueueDiscoveredFieldClosure* enqueue) { DiscoveredListIterator iter(refs_list, keep_alive, nullptr, enqueue); while (iter.has_next()) { iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); // keep the referent and followers around iter.make_referent_alive(); // Self-loop next, to mark the FinalReference not active. assert(java_lang_ref_Reference::next(iter.obj()) == nullptr, "enqueued FinalReference"); java_lang_ref_Reference::set_next_raw(iter.obj(), iter.obj()); iter.enqueue(); log_enqueued_ref(iter, "Final"); iter.next(); } iter.complete_enqueue(); refs_list.clear(); assert(iter.removed() == 0, "This phase does not remove anything."); return iter.removed(); } void ReferenceProcessor::clear_discovered_references(DiscoveredList& refs_list) { oop obj = nullptr; oop next = refs_list.head(); while (next != obj) { obj = next; next = java_lang_ref_Reference::discovered(obj); java_lang_ref_Reference::set_discovered_raw(obj, nullptr); } refs_list.clear(); } void ReferenceProcessor::abandon_partial_discovery() { // loop over the lists for (uint i = 0; i < _max_num_queues * number_of_subclasses_of_ref(); i++) { if ((i % _max_num_queues) == 0) { log_develop_trace(gc, ref)("Abandoning %s discovered list", list_name(i)); } clear_discovered_references(_discovered_refs[i]); } } size_t ReferenceProcessor::total_reference_count(ReferenceType type) const { DiscoveredList* list = nullptr; switch (type) { case REF_SOFT: list = _discoveredSoftRefs; break; case REF_WEAK: list = _discoveredWeakRefs; break; case REF_FINAL: list = _discoveredFinalRefs; break; case REF_PHANTOM: list = _discoveredPhantomRefs; break; case REF_NONE: default: ShouldNotReachHere(); } return total_count(list); } void RefProcTask::process_discovered_list(uint worker_id, ReferenceType ref_type, BoolObjectClosure* is_alive, OopClosure* keep_alive, EnqueueDiscoveredFieldClosure* enqueue) { ReferenceProcessor::RefProcSubPhases subphase; DiscoveredList* dl; switch (ref_type) { case ReferenceType::REF_SOFT: subphase = ReferenceProcessor::ProcessSoftRefSubPhase; dl = _ref_processor._discoveredSoftRefs; break; case ReferenceType::REF_WEAK: subphase = ReferenceProcessor::ProcessWeakRefSubPhase; dl = _ref_processor._discoveredWeakRefs; break; case ReferenceType::REF_FINAL: subphase = ReferenceProcessor::ProcessFinalRefSubPhase; dl = _ref_processor._discoveredFinalRefs; break; case ReferenceType::REF_PHANTOM: subphase = ReferenceProcessor::ProcessPhantomRefsSubPhase; dl = _ref_processor._discoveredPhantomRefs; break; default: ShouldNotReachHere(); } // Only Final refs are not enqueued and cleared here. bool do_enqueue_and_clear = (ref_type != REF_FINAL); { RefProcSubPhasesWorkerTimeTracker tt(subphase, _phase_times, tracker_id(worker_id)); size_t const removed = _ref_processor.process_discovered_list_work(dl[worker_id], is_alive, keep_alive, enqueue, do_enqueue_and_clear); _phase_times->add_ref_dropped(ref_type, removed); } } class RefProcSoftWeakFinalPhaseTask: public RefProcTask { public: RefProcSoftWeakFinalPhaseTask(ReferenceProcessor& ref_processor, ReferenceProcessorPhaseTimes* phase_times) : RefProcTask(ref_processor, phase_times) {} void rp_work(uint worker_id, BoolObjectClosure* is_alive, OopClosure* keep_alive, EnqueueDiscoveredFieldClosure* enqueue, VoidClosure* complete_gc) override { RefProcWorkerTimeTracker t(_phase_times->soft_weak_final_refs_phase_worker_time_sec(), tracker_id(worker_id)); process_discovered_list(worker_id, REF_SOFT, is_alive, keep_alive, enqueue); process_discovered_list(worker_id, REF_WEAK, is_alive, keep_alive, enqueue); process_discovered_list(worker_id, REF_FINAL, is_alive, keep_alive, enqueue); // Close the reachable set; needed for collectors which keep_alive_closure do // not immediately complete their work. complete_gc->do_void(); } }; class RefProcKeepAliveFinalPhaseTask: public RefProcTask { public: RefProcKeepAliveFinalPhaseTask(ReferenceProcessor& ref_processor, ReferenceProcessorPhaseTimes* phase_times) : RefProcTask(ref_processor, phase_times) {} void rp_work(uint worker_id, BoolObjectClosure* is_alive, OopClosure* keep_alive, EnqueueDiscoveredFieldClosure* enqueue, VoidClosure* complete_gc) override { RefProcSubPhasesWorkerTimeTracker tt(ReferenceProcessor::KeepAliveFinalRefsSubPhase, _phase_times, tracker_id(worker_id)); _ref_processor.process_final_keep_alive_work(_ref_processor._discoveredFinalRefs[worker_id], keep_alive, enqueue); // Close the reachable set complete_gc->do_void(); } }; class RefProcPhantomPhaseTask: public RefProcTask { public: RefProcPhantomPhaseTask(ReferenceProcessor& ref_processor, ReferenceProcessorPhaseTimes* phase_times) : RefProcTask(ref_processor, phase_times) {} void rp_work(uint worker_id, BoolObjectClosure* is_alive, OopClosure* keep_alive, EnqueueDiscoveredFieldClosure* enqueue, VoidClosure* complete_gc) override { process_discovered_list(worker_id, REF_PHANTOM, is_alive, keep_alive, enqueue); // Close the reachable set; needed for collectors which keep_alive_closure do // not immediately complete their work. complete_gc->do_void(); } }; void ReferenceProcessor::log_reflist(const char* prefix, DiscoveredList list[], uint num_active_queues) { LogTarget(Trace, gc, ref) lt; if (!lt.is_enabled()) { return; } size_t total = 0; LogStream ls(lt); ls.print("%s", prefix); for (uint i = 0; i < num_active_queues; i++) { ls.print("%zu ", list[i].length()); total += list[i].length(); } ls.print_cr("(%zu)", total); } #ifndef PRODUCT void ReferenceProcessor::log_reflist_counts(DiscoveredList ref_lists[], uint num_active_queues) { if (!log_is_enabled(Trace, gc, ref)) { return; } log_reflist("", ref_lists, num_active_queues); #ifdef ASSERT for (uint i = num_active_queues; i < _max_num_queues; i++) { assert(ref_lists[i].length() == 0, "%zu unexpected References in %u", ref_lists[i].length(), i); } #endif } #endif void ReferenceProcessor::set_active_mt_degree(uint v) { assert(v <= max_num_queues(), "Mt degree %u too high, maximum %u", v, max_num_queues()); _num_queues = v; _next_id = 0; } bool ReferenceProcessor::need_balance_queues(DiscoveredList refs_lists[]) { assert(processing_is_mt(), "why balance non-mt processing?"); // _num_queues is the processing degree. Only list entries up to // _num_queues will be processed, so any non-empty lists beyond // that must be redistributed to lists in that range. Even if not // needed for that, balancing may be desirable to eliminate poor // distribution of references among the lists. if (ParallelRefProcBalancingEnabled) { return true; // Configuration says do it. } else { // Configuration says don't balance, but if there are non-empty // lists beyond the processing degree, then must ignore the // configuration and balance anyway. for (uint i = _num_queues; i < _max_num_queues; ++i) { if (!refs_lists[i].is_empty()) { return true; // Must balance despite configuration. } } return false; // Safe to obey configuration and not balance. } } void ReferenceProcessor::maybe_balance_queues(DiscoveredList refs_lists[]) { assert(processing_is_mt(), "Should not call this otherwise"); if (need_balance_queues(refs_lists)) { balance_queues(refs_lists); } } // Balances reference queues. // Move entries from all queues[0, 1, ..., _max_num_q-1] to // queues[0, 1, ..., _num_q-1] because only the first _num_q // corresponding to the active workers will be processed. void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[]) { // calculate total length size_t total_refs = 0; log_develop_trace(gc, ref)("Balance ref_lists "); log_reflist_counts(ref_lists, _max_num_queues); for (uint i = 0; i < _max_num_queues; ++i) { total_refs += ref_lists[i].length(); } size_t avg_refs = total_refs / _num_queues + 1; uint to_idx = 0; for (uint from_idx = 0; from_idx < _max_num_queues; from_idx++) { bool move_all = false; if (from_idx >= _num_queues) { move_all = ref_lists[from_idx].length() > 0; } while ((ref_lists[from_idx].length() > avg_refs) || move_all) { assert(to_idx < _num_queues, "Sanity Check!"); if (ref_lists[to_idx].length() < avg_refs) { // move superfluous refs size_t refs_to_move; // Move all the Ref's if the from queue will not be processed. if (move_all) { refs_to_move = MIN2(ref_lists[from_idx].length(), avg_refs - ref_lists[to_idx].length()); } else { refs_to_move = MIN2(ref_lists[from_idx].length() - avg_refs, avg_refs - ref_lists[to_idx].length()); } assert(refs_to_move > 0, "otherwise the code below will fail"); oop move_head = ref_lists[from_idx].head(); oop move_tail = move_head; oop new_head = move_head; // find an element to split the list on for (size_t j = 0; j < refs_to_move; ++j) { move_tail = new_head; new_head = java_lang_ref_Reference::discovered(new_head); } // Add the chain to the to list. if (ref_lists[to_idx].head() == nullptr) { // to list is empty. Make a loop at the end. java_lang_ref_Reference::set_discovered_raw(move_tail, move_tail); } else { java_lang_ref_Reference::set_discovered_raw(move_tail, ref_lists[to_idx].head()); } ref_lists[to_idx].set_head(move_head); ref_lists[to_idx].inc_length(refs_to_move); // Remove the chain from the from list. if (move_tail == new_head) { // We found the end of the from list. ref_lists[from_idx].set_head(nullptr); } else { ref_lists[from_idx].set_head(new_head); } ref_lists[from_idx].dec_length(refs_to_move); if (ref_lists[from_idx].length() == 0) { break; } } else { to_idx = (to_idx + 1) % _num_queues; } } } #ifdef ASSERT log_reflist_counts(ref_lists, _num_queues); size_t balanced_total_refs = 0; for (uint i = 0; i < _num_queues; ++i) { balanced_total_refs += ref_lists[i].length(); } assert(total_refs == balanced_total_refs, "Balancing was incomplete"); #endif } void ReferenceProcessor::run_task(RefProcTask& task, RefProcProxyTask& proxy_task, bool marks_oops_alive) { log_debug(gc, ref)("ReferenceProcessor::execute queues: %d, %s, marks_oops_alive: %s", num_queues(), processing_is_mt() ? "RefProcThreadModel::Multi" : "RefProcThreadModel::Single", marks_oops_alive ? "true" : "false"); proxy_task.prepare_run_task(task, num_queues(), processing_is_mt() ? RefProcThreadModel::Multi : RefProcThreadModel::Single, marks_oops_alive); if (processing_is_mt()) { WorkerThreads* workers = Universe::heap()->safepoint_workers(); assert(workers != nullptr, "can not dispatch multi threaded without workers"); assert(workers->active_workers() >= num_queues(), "Ergonomically chosen workers(%u) should be less than or equal to active workers(%u)", num_queues(), workers->active_workers()); workers->run_task(&proxy_task, num_queues()); } else { for (unsigned i = 0; i < _max_num_queues; ++i) { proxy_task.work(i); } } } void ReferenceProcessor::process_soft_weak_final_refs(RefProcProxyTask& proxy_task, ReferenceProcessorPhaseTimes& phase_times) { size_t const num_soft_refs = phase_times.ref_discovered(REF_SOFT); size_t const num_weak_refs = phase_times.ref_discovered(REF_WEAK); size_t const num_final_refs = phase_times.ref_discovered(REF_FINAL); size_t const num_total_refs = num_soft_refs + num_weak_refs + num_final_refs; if (num_total_refs == 0) { log_debug(gc, ref)("Skipped SoftWeakFinalRefsPhase of Reference Processing: no references"); return; } RefProcMTDegreeAdjuster a(this, SoftWeakFinalRefsPhase, num_total_refs); if (processing_is_mt()) { RefProcBalanceQueuesTimeTracker tt(SoftWeakFinalRefsPhase, &phase_times); maybe_balance_queues(_discoveredSoftRefs); maybe_balance_queues(_discoveredWeakRefs); maybe_balance_queues(_discoveredFinalRefs); } log_reflist("SoftWeakFinalRefsPhase Soft before", _discoveredSoftRefs, _max_num_queues); log_reflist("SoftWeakFinalRefsPhase Weak before", _discoveredWeakRefs, _max_num_queues); log_reflist("SoftWeakFinalRefsPhase Final before", _discoveredFinalRefs, _max_num_queues); RefProcSoftWeakFinalPhaseTask phase_task(*this, &phase_times); run_task(phase_task, proxy_task, false); verify_total_count_zero(_discoveredSoftRefs, "SoftReference"); verify_total_count_zero(_discoveredWeakRefs, "WeakReference"); log_reflist("SoftWeakFinalRefsPhase Final after", _discoveredFinalRefs, _max_num_queues); } void ReferenceProcessor::process_final_keep_alive(RefProcProxyTask& proxy_task, ReferenceProcessorPhaseTimes& phase_times) { size_t const num_final_refs = phase_times.ref_discovered(REF_FINAL); if (num_final_refs == 0) { log_debug(gc, ref)("Skipped KeepAliveFinalRefsPhase of Reference Processing: no references"); return; } RefProcMTDegreeAdjuster a(this, KeepAliveFinalRefsPhase, num_final_refs); if (processing_is_mt()) { RefProcBalanceQueuesTimeTracker tt(KeepAliveFinalRefsPhase, &phase_times); maybe_balance_queues(_discoveredFinalRefs); } // Traverse referents of final references and keep them and followers alive. RefProcKeepAliveFinalPhaseTask phase_task(*this, &phase_times); run_task(phase_task, proxy_task, true); verify_total_count_zero(_discoveredFinalRefs, "FinalReference"); } void ReferenceProcessor::process_phantom_refs(RefProcProxyTask& proxy_task, ReferenceProcessorPhaseTimes& phase_times) { size_t const num_phantom_refs = phase_times.ref_discovered(REF_PHANTOM); if (num_phantom_refs == 0) { log_debug(gc, ref)("Skipped PhantomRefsPhase of Reference Processing: no references"); return; } RefProcMTDegreeAdjuster a(this, PhantomRefsPhase, num_phantom_refs); if (processing_is_mt()) { RefProcBalanceQueuesTimeTracker tt(PhantomRefsPhase, &phase_times); maybe_balance_queues(_discoveredPhantomRefs); } log_reflist("PhantomRefsPhase Phantom before", _discoveredPhantomRefs, _max_num_queues); RefProcPhantomPhaseTask phase_task(*this, &phase_times); run_task(phase_task, proxy_task, false); verify_total_count_zero(_discoveredPhantomRefs, "PhantomReference"); } inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) { uint id = 0; // Determine the queue index to use for this object. if (_discovery_is_mt) { // During a multi-threaded discovery phase, // each thread saves to its "own" list. id = WorkerThread::worker_id(); } else { // single-threaded discovery, we save in round-robin // fashion to each of the lists. if (processing_is_mt()) { id = next_id(); } } assert(id < _max_num_queues, "Id is out of bounds id %u and max id %u)", id, _max_num_queues); // Get the discovered queue to which we will add DiscoveredList* list = nullptr; switch (rt) { 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(); } log_develop_trace(gc, ref)("Thread %d gets list " PTR_FORMAT, id, p2i(list)); return list; } inline bool ReferenceProcessor::set_discovered_link(HeapWord* discovered_addr, oop next_discovered) { return discovery_is_mt() ? set_discovered_link_mt(discovered_addr, next_discovered) : set_discovered_link_st(discovered_addr, next_discovered); } inline void ReferenceProcessor::add_to_discovered_list(DiscoveredList& refs_list, oop obj, HeapWord* discovered_addr) { oop current_head = refs_list.head(); // Prepare value to put into the discovered field. The last ref must have its // discovered field pointing to itself. oop next_discovered = (current_head != nullptr) ? current_head : obj; bool added = set_discovered_link(discovered_addr, next_discovered); if (added) { // We can always add the object without synchronization: every thread has its // own list head. refs_list.add_as_head(obj); log_develop_trace(gc, ref)("Discovered reference (%s) (" PTR_FORMAT ": %s)", discovery_is_mt() ? "mt" : "st", p2i(obj), obj->klass()->internal_name()); } else { log_develop_trace(gc, ref)("Already discovered reference (mt) (" PTR_FORMAT ": %s)", p2i(obj), obj->klass()->internal_name()); } } inline bool ReferenceProcessor::set_discovered_link_st(HeapWord* discovered_addr, oop next_discovered) { assert(!discovery_is_mt(), "must be"); if (discovery_is_stw()) { // Do a raw store here: the field will be visited later when processing // the discovered references. RawAccess<>::oop_store(discovered_addr, next_discovered); } else { HeapAccess::oop_store(discovered_addr, next_discovered); } // Always successful. return true; } inline bool ReferenceProcessor::set_discovered_link_mt(HeapWord* discovered_addr, oop next_discovered) { assert(discovery_is_mt(), "must be"); // We must make sure this object is only enqueued once. Try to CAS into the discovered_addr. oop retest; if (discovery_is_stw()) { // Try a raw store here, still making sure that we enqueue only once: the field // will be visited later when processing the discovered references. retest = RawAccess<>::oop_atomic_cmpxchg(discovered_addr, oop(nullptr), next_discovered); } else { retest = HeapAccess::oop_atomic_cmpxchg(discovered_addr, oop(nullptr), next_discovered); } return retest == nullptr; } #ifndef PRODUCT // Concurrent discovery might allow us to observe j.l.References with null // referents, being those cleared concurrently by mutators during (or after) discovery. void ReferenceProcessor::verify_referent(oop obj) { bool concurrent = discovery_is_concurrent(); oop referent = java_lang_ref_Reference::unknown_referent_no_keepalive(obj); assert(concurrent ? oopDesc::is_oop_or_null(referent) : oopDesc::is_oop(referent), "Bad referent " PTR_FORMAT " found in Reference " PTR_FORMAT " during %sconcurrent discovery ", p2i(referent), p2i(obj), concurrent ? "" : "non-"); } #endif bool ReferenceProcessor::is_subject_to_discovery(oop const obj) const { return _is_subject_to_discovery->do_object_b(obj); } // Reference discovery policy: // if the reference object is not in the "originating generation" // (or part of the heap being collected, indicated by our "span") // we don't treat it specially (i.e. we scan it as we would // a normal oop, treating its references as strong references). // This means that references can't be discovered unless their // referent is also in the same span. This is the simplest, // most "local" and most conservative approach, albeit one // that may cause weak references to be enqueued least promptly. // We call this choice the "ReferenceBasedDiscovery" policy. bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) { // Make sure we are discovering refs (rather than processing discovered refs). if (!_discovering_refs || !RegisterReferences) { return false; } if ((rt == REF_FINAL) && (java_lang_ref_Reference::next(obj) != nullptr)) { // Don't rediscover non-active FinalReferences. return false; } if (!is_subject_to_discovery(obj)) { // Reference is not in the originating generation; // don't treat it specially (i.e. we want to scan it as a normal // object with strong references). return false; } // We only discover references whose referents are not (yet) // known to be strongly reachable. if (is_alive_non_header() != nullptr) { verify_referent(obj); oop referent = java_lang_ref_Reference::unknown_referent_no_keepalive(obj); if (is_alive_non_header()->do_object_b(referent)) { return false; // referent is reachable } } if (rt == REF_SOFT) { // For soft refs we can decide now if these are not // current candidates for clearing, in which case we // can mark through them now, rather than delaying that // to the reference-processing phase. Since all current // time-stamp policies advance the soft-ref clock only // at a full collection cycle, this is always currently // accurate. if (!_current_soft_ref_policy->should_clear_reference(obj, _soft_ref_timestamp_clock)) { return false; } } ResourceMark rm; // Needed for tracing. HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr_raw(obj); const oop discovered = java_lang_ref_Reference::discovered(obj); assert(oopDesc::is_oop_or_null(discovered), "Expected an oop or null for discovered field at " PTR_FORMAT, p2i(discovered)); if (discovered != nullptr) { // The reference has already been discovered... log_develop_trace(gc, ref)("Already discovered reference (" PTR_FORMAT ": %s)", p2i(obj), obj->klass()->internal_name()); // Encountering an already-discovered non-strong ref because G1 can restart // concurrent marking on marking-stack overflow. Must continue to treat // this non-strong ref as discovered to avoid keeping the referent // unnecessarily alive. assert(UseG1GC, "inv"); assert(_discovery_is_concurrent, "inv"); return true; } // Get the right type of discovered queue head. DiscoveredList* list = get_discovered_list(rt); add_to_discovered_list(*list, obj, discovered_addr); assert(oopDesc::is_oop(obj), "Discovered a bad reference"); verify_referent(obj); return true; } void ReferenceProcessor::preclean_discovered_references(BoolObjectClosure* is_alive, EnqueueDiscoveredFieldClosure* enqueue, YieldClosure* yield, GCTimer* gc_timer) { // These lists can be handled here in any order and, indeed, concurrently. // Soft references { GCTraceTime(Debug, gc, ref) tm("Preclean SoftReferences", gc_timer); log_reflist("SoftRef before: ", _discoveredSoftRefs, _max_num_queues); for (uint i = 0; i < _max_num_queues; i++) { if (yield->should_return()) { return; } if (preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive, enqueue, yield)) { log_reflist("SoftRef abort: ", _discoveredSoftRefs, _max_num_queues); return; } } log_reflist("SoftRef after: ", _discoveredSoftRefs, _max_num_queues); } // Weak references { GCTraceTime(Debug, gc, ref) tm("Preclean WeakReferences", gc_timer); log_reflist("WeakRef before: ", _discoveredWeakRefs, _max_num_queues); for (uint i = 0; i < _max_num_queues; i++) { if (yield->should_return()) { return; } if (preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive, enqueue, yield)) { log_reflist("WeakRef abort: ", _discoveredWeakRefs, _max_num_queues); return; } } log_reflist("WeakRef after: ", _discoveredWeakRefs, _max_num_queues); } // Final references { GCTraceTime(Debug, gc, ref) tm("Preclean FinalReferences", gc_timer); log_reflist("FinalRef before: ", _discoveredFinalRefs, _max_num_queues); for (uint i = 0; i < _max_num_queues; i++) { if (yield->should_return()) { return; } if (preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive, enqueue, yield)) { log_reflist("FinalRef abort: ", _discoveredFinalRefs, _max_num_queues); return; } } log_reflist("FinalRef after: ", _discoveredFinalRefs, _max_num_queues); } // Phantom references { GCTraceTime(Debug, gc, ref) tm("Preclean PhantomReferences", gc_timer); log_reflist("PhantomRef before: ", _discoveredPhantomRefs, _max_num_queues); for (uint i = 0; i < _max_num_queues; i++) { if (yield->should_return()) { return; } if (preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive, enqueue, yield)) { log_reflist("PhantomRef abort: ", _discoveredPhantomRefs, _max_num_queues); return; } } log_reflist("PhantomRef after: ", _discoveredPhantomRefs, _max_num_queues); } } bool ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list, BoolObjectClosure* is_alive, EnqueueDiscoveredFieldClosure* enqueue, YieldClosure* yield) { DiscoveredListIterator iter(refs_list, nullptr /* keep_alive */, is_alive, enqueue); while (iter.has_next()) { if (yield->should_return_fine_grain()) { return true; } iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); if (iter.referent() == nullptr) { log_preclean_ref(iter, "cleared"); iter.remove(); iter.move_to_next(); } else if (iter.is_referent_alive()) { log_preclean_ref(iter, "reachable"); iter.remove(); iter.move_to_next(); } else { iter.next(); } } if (iter.processed() > 0) { log_develop_trace(gc, ref)(" Dropped %zu Refs out of %zu Refs in discovered list " PTR_FORMAT, iter.removed(), iter.processed(), p2i(&refs_list)); } return false; } const char* ReferenceProcessor::list_name(uint i) { assert(i <= _max_num_queues * number_of_subclasses_of_ref(), "Out of bounds index"); int j = i / _max_num_queues; switch (j) { case 0: return "SoftRef"; case 1: return "WeakRef"; case 2: return "FinalRef"; case 3: return "PhantomRef"; } ShouldNotReachHere(); return nullptr; } uint RefProcMTDegreeAdjuster::ergo_proc_thread_count(size_t ref_count, uint max_threads, RefProcPhases phase) const { assert(0 < max_threads, "must allow at least one thread"); if (use_max_threads(phase) || (ReferencesPerThread == 0)) { return max_threads; } size_t thread_count = 1 + (ref_count / ReferencesPerThread); return (uint)MIN3(thread_count, static_cast(max_threads), (size_t)os::active_processor_count()); } bool RefProcMTDegreeAdjuster::use_max_threads(RefProcPhases phase) const { // Even a small number of references in this phase could produce large amounts of work. return phase == ReferenceProcessor::KeepAliveFinalRefsPhase; } RefProcMTDegreeAdjuster::RefProcMTDegreeAdjuster(ReferenceProcessor* rp, RefProcPhases phase, size_t ref_count): _rp(rp), _saved_num_queues(_rp->num_queues()) { uint workers = ergo_proc_thread_count(ref_count, _rp->num_queues(), phase); _rp->set_active_mt_degree(workers); } RefProcMTDegreeAdjuster::~RefProcMTDegreeAdjuster() { // Revert to previous status. _rp->set_active_mt_degree(_saved_num_queues); }