/* * Copyright (c) 2001, 2018, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. * */ #include "precompiled.hpp" #include "classfile/javaClasses.inline.hpp" #include "classfile/systemDictionary.hpp" #include "gc/shared/collectedHeap.hpp" #include "gc/shared/collectedHeap.inline.hpp" #include "gc/shared/gcTimer.hpp" #include "gc/shared/gcTraceTime.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 "oops/access.inline.hpp" #include "oops/oop.inline.hpp" #include "runtime/java.hpp" ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL; ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy = NULL; jlong ReferenceProcessor::_soft_ref_timestamp_clock = 0; void referenceProcessor_init() { ReferenceProcessor::init_statics(); } void ReferenceProcessor::init_statics() { // We need a monotonically non-decreasing time in ms but // os::javaTimeMillis() does not guarantee monotonicity. jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; // Initialize the soft ref timestamp clock. _soft_ref_timestamp_clock = now; // Also update the soft ref clock in j.l.r.SoftReference java_lang_ref_SoftReference::set_clock(_soft_ref_timestamp_clock); _always_clear_soft_ref_policy = new AlwaysClearPolicy(); if (is_server_compilation_mode_vm()) { _default_soft_ref_policy = new LRUMaxHeapPolicy(); } else { _default_soft_ref_policy = new LRUCurrentHeapPolicy(); } if (_always_clear_soft_ref_policy == NULL || _default_soft_ref_policy == NULL) { vm_exit_during_initialization("Could not allocate reference policy object"); } guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery || RefDiscoveryPolicy == ReferentBasedDiscovery, "Unrecognized RefDiscoveryPolicy"); } void ReferenceProcessor::enable_discovery(bool check_no_refs) { #ifdef ASSERT // Verify that we're not currently discovering refs assert(!_discovering_refs, "nested call?"); if (check_no_refs) { // Verify that the discovered lists are empty verify_no_references_recorded(); } #endif // ASSERT // Someone could have modified the value of the static // field in the j.l.r.SoftReference class that holds the // soft reference timestamp clock using reflection or // Unsafe between GCs. Unconditionally update the static // field in ReferenceProcessor here so that we use the new // value during reference discovery. _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock(); _discovering_refs = true; } ReferenceProcessor::ReferenceProcessor(BoolObjectClosure* is_subject_to_discovery, bool mt_processing, uint mt_processing_degree, bool mt_discovery, uint mt_discovery_degree, bool atomic_discovery, BoolObjectClosure* is_alive_non_header, bool adjust_no_of_processing_threads) : _is_subject_to_discovery(is_subject_to_discovery), _discovering_refs(false), _enqueuing_is_done(false), _processing_is_mt(mt_processing), _next_id(0), _adjust_no_of_processing_threads(adjust_no_of_processing_threads), _is_alive_non_header(is_alive_non_header) { assert(is_subject_to_discovery != NULL, "must be set"); _discovery_is_atomic = atomic_discovery; _discovery_is_mt = mt_discovery; _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); if (_discovered_refs == NULL) { vm_exit_during_initialization("Could not allocated RefProc Array"); } _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 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; jlong soft_ref_clock = java_lang_ref_SoftReference::clock(); assert(soft_ref_clock == _soft_ref_timestamp_clock, "soft ref clocks out of sync"); NOT_PRODUCT( if (now < _soft_ref_timestamp_clock) { 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 " SIZE_FORMAT " elements", type, count); } #endif ReferenceProcessorStats ReferenceProcessor::process_discovered_references( BoolObjectClosure* is_alive, OopClosure* keep_alive, VoidClosure* complete_gc, AbstractRefProcTaskExecutor* task_executor, ReferenceProcessorPhaseTimes* phase_times) { double start_time = os::elapsedTime(); assert(!enqueuing_is_done(), "If here enqueuing should not be complete"); // Stop treating discovered references specially. disable_discovery(); // If discovery was concurrent, someone could have modified // the value of the static field in the j.l.r.SoftReference // class that holds the soft reference timestamp clock using // reflection or Unsafe between when discovery was enabled and // now. Unconditionally update the static field in ReferenceProcessor // here so that we use the new value during processing of the // discovered soft refs. _soft_ref_timestamp_clock = java_lang_ref_SoftReference::clock(); ReferenceProcessorStats stats(total_count(_discoveredSoftRefs), total_count(_discoveredWeakRefs), total_count(_discoveredFinalRefs), total_count(_discoveredPhantomRefs)); { RefProcTotalPhaseTimesTracker tt(RefPhase1, phase_times, this); process_soft_ref_reconsider(is_alive, keep_alive, complete_gc, task_executor, phase_times); } update_soft_ref_master_clock(); { RefProcTotalPhaseTimesTracker tt(RefPhase2, phase_times, this); process_soft_weak_final_refs(is_alive, keep_alive, complete_gc, task_executor, phase_times); } { RefProcTotalPhaseTimesTracker tt(RefPhase3, phase_times, this); process_final_keep_alive(keep_alive, complete_gc, task_executor, phase_times); } { RefProcTotalPhaseTimesTracker tt(RefPhase4, phase_times, this); process_phantom_refs(is_alive, keep_alive, complete_gc, task_executor, phase_times); } if (task_executor != NULL) { // Record the work done by the parallel workers. task_executor->set_single_threaded_mode(); } phase_times->set_total_time_ms((os::elapsedTime() - start_time) * 1000); return stats; } 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_addr = java_lang_ref_Reference::referent_addr_raw(_current_discovered); _referent = java_lang_ref_Reference::referent(_current_discovered); assert(Universe::heap()->is_in_reserved_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(NULL)); // First _prev_next ref actually points into DiscoveredList (gross). oop new_next; if (oopDesc::equals_raw(_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. Note that G1 does not need a // pre-barrier here because we know the Reference has already been found/marked, // that's how it ended up in the discovered list in the first place. RawAccess<>::oop_store(_prev_discovered_addr, new_next); _removed++; _refs_list.dec_length(1); } void DiscoveredListIterator::clear_referent() { RawAccess<>::oop_store(_referent_addr, oop(NULL)); } void DiscoveredListIterator::enqueue() { HeapAccess::oop_store_at(_current_discovered, java_lang_ref_Reference::discovered_offset, _next_discovered); } void DiscoveredListIterator::complete_enqueue() { if (_prev_discovered != NULL) { // 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()); HeapAccess::oop_store_at(_prev_discovered, java_lang_ref_Reference::discovered_offset, old); } } 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 (" INTPTR_FORMAT ": %s)", reason, p2i(iter.obj()), iter.obj()->klass()->internal_name()); } assert(oopDesc::is_oop(iter.obj(), UseConcMarkSweepGC), "Adding a bad reference"); } size_t ReferenceProcessor::process_soft_ref_reconsider_work(DiscoveredList& refs_list, ReferencePolicy* policy, BoolObjectClosure* is_alive, OopClosure* keep_alive, VoidClosure* complete_gc) { assert(policy != NULL, "Must have a non-NULL policy"); DiscoveredListIterator iter(refs_list, keep_alive, is_alive); // Decide which softly reachable refs should be kept alive. while (iter.has_next()) { iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */)); bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive(); if (referent_is_dead && !policy->should_clear_reference(iter.obj(), _soft_ref_timestamp_clock)) { log_dropped_ref(iter, "by policy"); // Remove Reference object from list iter.remove(); // keep the referent around iter.make_referent_alive(); iter.move_to_next(); } else { iter.next(); } } // Close the reachable set complete_gc->do_void(); log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " dead Refs out of " SIZE_FORMAT " discovered Refs by policy, from list " INTPTR_FORMAT, iter.removed(), iter.processed(), p2i(&refs_list)); return iter.removed(); } size_t ReferenceProcessor::process_soft_weak_final_refs_work(DiscoveredList& refs_list, BoolObjectClosure* is_alive, OopClosure* keep_alive, bool do_enqueue_and_clear) { DiscoveredListIterator iter(refs_list, keep_alive, is_alive); while (iter.has_next()) { iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */)); if (iter.referent() == NULL) { // Reference has been cleared since discovery; only possible if // discovery is not atomic (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 " SIZE_FORMAT " active Refs out of " SIZE_FORMAT " Refs in discovered list " INTPTR_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, VoidClosure* complete_gc) { DiscoveredListIterator iter(refs_list, keep_alive, NULL); 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()) == NULL, "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(); // Close the reachable set complete_gc->do_void(); refs_list.clear(); assert(iter.removed() == 0, "This phase does not remove anything."); return iter.removed(); } size_t ReferenceProcessor::process_phantom_refs_work(DiscoveredList& refs_list, BoolObjectClosure* is_alive, OopClosure* keep_alive, VoidClosure* complete_gc) { DiscoveredListIterator iter(refs_list, keep_alive, is_alive); while (iter.has_next()) { iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */)); oop const referent = iter.referent(); if (referent == NULL || iter.is_referent_alive()) { iter.make_referent_alive(); iter.remove(); iter.move_to_next(); } else { iter.clear_referent(); iter.enqueue(); log_enqueued_ref(iter, "cleared Phantom"); iter.next(); } } iter.complete_enqueue(); // Close the reachable set; needed for collectors which keep_alive_closure do // not immediately complete their work. complete_gc->do_void(); refs_list.clear(); return iter.removed(); } void ReferenceProcessor::clear_discovered_references(DiscoveredList& refs_list) { oop obj = NULL; oop next = refs_list.head(); while (!oopDesc::equals_raw(next, obj)) { obj = next; next = java_lang_ref_Reference::discovered(obj); java_lang_ref_Reference::set_discovered_raw(obj, NULL); } 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 = NULL; 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_OTHER: case REF_NONE: default: ShouldNotReachHere(); } return total_count(list); } class RefProcPhase1Task : public AbstractRefProcTaskExecutor::ProcessTask { public: RefProcPhase1Task(ReferenceProcessor& ref_processor, ReferenceProcessorPhaseTimes* phase_times, ReferencePolicy* policy) : ProcessTask(ref_processor, true /* marks_oops_alive */, phase_times), _policy(policy) { } virtual void work(uint worker_id, BoolObjectClosure& is_alive, OopClosure& keep_alive, VoidClosure& complete_gc) { RefProcSubPhasesWorkerTimeTracker tt(ReferenceProcessor::SoftRefSubPhase1, _phase_times, worker_id); size_t const removed = _ref_processor.process_soft_ref_reconsider_work(_ref_processor._discoveredSoftRefs[worker_id], _policy, &is_alive, &keep_alive, &complete_gc); _phase_times->add_ref_cleared(REF_SOFT, removed); } private: ReferencePolicy* _policy; }; class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask { void run_phase2(uint worker_id, DiscoveredList list[], BoolObjectClosure& is_alive, OopClosure& keep_alive, bool do_enqueue_and_clear, ReferenceType ref_type) { size_t const removed = _ref_processor.process_soft_weak_final_refs_work(list[worker_id], &is_alive, &keep_alive, do_enqueue_and_clear); _phase_times->add_ref_cleared(ref_type, removed); } public: RefProcPhase2Task(ReferenceProcessor& ref_processor, ReferenceProcessorPhaseTimes* phase_times) : ProcessTask(ref_processor, false /* marks_oops_alive */, phase_times) { } virtual void work(uint worker_id, BoolObjectClosure& is_alive, OopClosure& keep_alive, VoidClosure& complete_gc) { RefProcWorkerTimeTracker t(_phase_times->phase2_worker_time_sec(), worker_id); { RefProcSubPhasesWorkerTimeTracker tt(ReferenceProcessor::SoftRefSubPhase2, _phase_times, worker_id); run_phase2(worker_id, _ref_processor._discoveredSoftRefs, is_alive, keep_alive, true /* do_enqueue_and_clear */, REF_SOFT); } { RefProcSubPhasesWorkerTimeTracker tt(ReferenceProcessor::WeakRefSubPhase2, _phase_times, worker_id); run_phase2(worker_id, _ref_processor._discoveredWeakRefs, is_alive, keep_alive, true /* do_enqueue_and_clear */, REF_WEAK); } { RefProcSubPhasesWorkerTimeTracker tt(ReferenceProcessor::FinalRefSubPhase2, _phase_times, worker_id); run_phase2(worker_id, _ref_processor._discoveredFinalRefs, is_alive, keep_alive, false /* do_enqueue_and_clear */, REF_FINAL); } // Close the reachable set; needed for collectors which keep_alive_closure do // not immediately complete their work. complete_gc.do_void(); } }; class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask { public: RefProcPhase3Task(ReferenceProcessor& ref_processor, ReferenceProcessorPhaseTimes* phase_times) : ProcessTask(ref_processor, true /* marks_oops_alive */, phase_times) { } virtual void work(uint worker_id, BoolObjectClosure& is_alive, OopClosure& keep_alive, VoidClosure& complete_gc) { RefProcSubPhasesWorkerTimeTracker tt(ReferenceProcessor::FinalRefSubPhase3, _phase_times, worker_id); _ref_processor.process_final_keep_alive_work(_ref_processor._discoveredFinalRefs[worker_id], &keep_alive, &complete_gc); } }; class RefProcPhase4Task: public AbstractRefProcTaskExecutor::ProcessTask { public: RefProcPhase4Task(ReferenceProcessor& ref_processor, ReferenceProcessorPhaseTimes* phase_times) : ProcessTask(ref_processor, false /* marks_oops_alive */, phase_times) { } virtual void work(uint worker_id, BoolObjectClosure& is_alive, OopClosure& keep_alive, VoidClosure& complete_gc) { RefProcSubPhasesWorkerTimeTracker tt(ReferenceProcessor::PhantomRefSubPhase4, _phase_times, worker_id); size_t const removed = _ref_processor.process_phantom_refs_work(_ref_processor._discoveredPhantomRefs[worker_id], &is_alive, &keep_alive, &complete_gc); _phase_times->add_ref_cleared(REF_PHANTOM, removed); } }; 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(SIZE_FORMAT " ", list[i].length()); total += list[i].length(); } ls.print_cr("(" SIZE_FORMAT ")", 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, SIZE_FORMAT " unexpected References in %u", ref_lists[i].length(), i); } #endif } #endif void ReferenceProcessor::set_active_mt_degree(uint v) { _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() == NULL) { // to list is empty. Make a loop at the end. java_lang_ref_Reference::set_discovered_raw(move_tail, move_tail); } else { java_lang_ref_Reference::set_discovered_raw(move_tail, ref_lists[to_idx].head()); } ref_lists[to_idx].set_head(move_head); ref_lists[to_idx].inc_length(refs_to_move); // Remove the chain from the from list. if (oopDesc::equals_raw(move_tail, new_head)) { // We found the end of the from list. ref_lists[from_idx].set_head(NULL); } else { ref_lists[from_idx].set_head(new_head); } ref_lists[from_idx].dec_length(refs_to_move); if (ref_lists[from_idx].length() == 0) { break; } } else { to_idx = (to_idx + 1) % _num_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 } bool ReferenceProcessor::is_mt_processing_set_up(AbstractRefProcTaskExecutor* task_executor) const { return task_executor != NULL && _processing_is_mt; } void ReferenceProcessor::process_soft_ref_reconsider(BoolObjectClosure* is_alive, OopClosure* keep_alive, VoidClosure* complete_gc, AbstractRefProcTaskExecutor* task_executor, ReferenceProcessorPhaseTimes* phase_times) { assert(!_processing_is_mt || task_executor != NULL, "Task executor must not be NULL when mt processing is set."); size_t const num_soft_refs = total_count(_discoveredSoftRefs); phase_times->set_ref_discovered(REF_SOFT, num_soft_refs); phase_times->set_processing_is_mt(_processing_is_mt); if (num_soft_refs == 0 || _current_soft_ref_policy == NULL) { log_debug(gc, ref)("Skipped phase1 of Reference Processing due to unavailable references"); return; } RefProcMTDegreeAdjuster a(this, RefPhase1, num_soft_refs); if (_processing_is_mt) { RefProcBalanceQueuesTimeTracker tt(RefPhase1, phase_times); maybe_balance_queues(_discoveredSoftRefs); } RefProcPhaseTimeTracker tt(RefPhase1, phase_times); log_reflist("Phase1 Soft before", _discoveredSoftRefs, _max_num_queues); if (_processing_is_mt) { RefProcPhase1Task phase1(*this, phase_times, _current_soft_ref_policy); task_executor->execute(phase1, num_queues()); } else { size_t removed = 0; RefProcSubPhasesWorkerTimeTracker tt2(SoftRefSubPhase1, phase_times, 0); for (uint i = 0; i < _max_num_queues; i++) { removed += process_soft_ref_reconsider_work(_discoveredSoftRefs[i], _current_soft_ref_policy, is_alive, keep_alive, complete_gc); } phase_times->add_ref_cleared(REF_SOFT, removed); } log_reflist("Phase1 Soft after", _discoveredSoftRefs, _max_num_queues); } void ReferenceProcessor::process_soft_weak_final_refs(BoolObjectClosure* is_alive, OopClosure* keep_alive, VoidClosure* complete_gc, AbstractRefProcTaskExecutor* task_executor, ReferenceProcessorPhaseTimes* phase_times) { assert(!_processing_is_mt || task_executor != NULL, "Task executor must not be NULL when mt processing is set."); size_t const num_soft_refs = total_count(_discoveredSoftRefs); size_t const num_weak_refs = total_count(_discoveredWeakRefs); size_t const num_final_refs = total_count(_discoveredFinalRefs); size_t const num_total_refs = num_soft_refs + num_weak_refs + num_final_refs; phase_times->set_ref_discovered(REF_WEAK, num_weak_refs); phase_times->set_ref_discovered(REF_FINAL, num_final_refs); phase_times->set_processing_is_mt(_processing_is_mt); if (num_total_refs == 0) { log_debug(gc, ref)("Skipped phase2 of Reference Processing due to unavailable references"); return; } RefProcMTDegreeAdjuster a(this, RefPhase2, num_total_refs); if (_processing_is_mt) { RefProcBalanceQueuesTimeTracker tt(RefPhase2, phase_times); maybe_balance_queues(_discoveredSoftRefs); maybe_balance_queues(_discoveredWeakRefs); maybe_balance_queues(_discoveredFinalRefs); } RefProcPhaseTimeTracker tt(RefPhase2, phase_times); log_reflist("Phase2 Soft before", _discoveredSoftRefs, _max_num_queues); log_reflist("Phase2 Weak before", _discoveredWeakRefs, _max_num_queues); log_reflist("Phase2 Final before", _discoveredFinalRefs, _max_num_queues); if (_processing_is_mt) { RefProcPhase2Task phase2(*this, phase_times); task_executor->execute(phase2, num_queues()); } else { RefProcWorkerTimeTracker t(phase_times->phase2_worker_time_sec(), 0); { size_t removed = 0; RefProcSubPhasesWorkerTimeTracker tt2(SoftRefSubPhase2, phase_times, 0); for (uint i = 0; i < _max_num_queues; i++) { removed += process_soft_weak_final_refs_work(_discoveredSoftRefs[i], is_alive, keep_alive, true /* do_enqueue */); } phase_times->add_ref_cleared(REF_SOFT, removed); } { size_t removed = 0; RefProcSubPhasesWorkerTimeTracker tt2(WeakRefSubPhase2, phase_times, 0); for (uint i = 0; i < _max_num_queues; i++) { removed += process_soft_weak_final_refs_work(_discoveredWeakRefs[i], is_alive, keep_alive, true /* do_enqueue */); } phase_times->add_ref_cleared(REF_WEAK, removed); } { size_t removed = 0; RefProcSubPhasesWorkerTimeTracker tt2(FinalRefSubPhase2, phase_times, 0); for (uint i = 0; i < _max_num_queues; i++) { removed += process_soft_weak_final_refs_work(_discoveredFinalRefs[i], is_alive, keep_alive, false /* do_enqueue */); } phase_times->add_ref_cleared(REF_FINAL, removed); } complete_gc->do_void(); } verify_total_count_zero(_discoveredSoftRefs, "SoftReference"); verify_total_count_zero(_discoveredWeakRefs, "WeakReference"); log_reflist("Phase2 Final after", _discoveredFinalRefs, _max_num_queues); } void ReferenceProcessor::process_final_keep_alive(OopClosure* keep_alive, VoidClosure* complete_gc, AbstractRefProcTaskExecutor* task_executor, ReferenceProcessorPhaseTimes* phase_times) { assert(!_processing_is_mt || task_executor != NULL, "Task executor must not be NULL when mt processing is set."); size_t const num_final_refs = total_count(_discoveredFinalRefs); phase_times->set_processing_is_mt(_processing_is_mt); if (num_final_refs == 0) { log_debug(gc, ref)("Skipped phase3 of Reference Processing due to unavailable references"); return; } RefProcMTDegreeAdjuster a(this, RefPhase3, num_final_refs); if (_processing_is_mt) { RefProcBalanceQueuesTimeTracker tt(RefPhase3, phase_times); maybe_balance_queues(_discoveredFinalRefs); } // Phase 3: // . Traverse referents of final references and keep them and followers alive. RefProcPhaseTimeTracker tt(RefPhase3, phase_times); if (_processing_is_mt) { RefProcPhase3Task phase3(*this, phase_times); task_executor->execute(phase3, num_queues()); } else { RefProcSubPhasesWorkerTimeTracker tt2(FinalRefSubPhase3, phase_times, 0); for (uint i = 0; i < _max_num_queues; i++) { process_final_keep_alive_work(_discoveredFinalRefs[i], keep_alive, complete_gc); } } verify_total_count_zero(_discoveredFinalRefs, "FinalReference"); } void ReferenceProcessor::process_phantom_refs(BoolObjectClosure* is_alive, OopClosure* keep_alive, VoidClosure* complete_gc, AbstractRefProcTaskExecutor* task_executor, ReferenceProcessorPhaseTimes* phase_times) { assert(!_processing_is_mt || task_executor != NULL, "Task executor must not be NULL when mt processing is set."); size_t const num_phantom_refs = total_count(_discoveredPhantomRefs); phase_times->set_ref_discovered(REF_PHANTOM, num_phantom_refs); phase_times->set_processing_is_mt(_processing_is_mt); if (num_phantom_refs == 0) { log_debug(gc, ref)("Skipped phase4 of Reference Processing due to unavailable references"); return; } RefProcMTDegreeAdjuster a(this, RefPhase4, num_phantom_refs); if (_processing_is_mt) { RefProcBalanceQueuesTimeTracker tt(RefPhase4, phase_times); maybe_balance_queues(_discoveredPhantomRefs); } // Phase 4: Walk phantom references appropriately. RefProcPhaseTimeTracker tt(RefPhase4, phase_times); log_reflist("Phase4 Phantom before", _discoveredPhantomRefs, _max_num_queues); if (_processing_is_mt) { RefProcPhase4Task phase4(*this, phase_times); task_executor->execute(phase4, num_queues()); } else { size_t removed = 0; RefProcSubPhasesWorkerTimeTracker tt(PhantomRefSubPhase4, phase_times, 0); for (uint i = 0; i < _max_num_queues; i++) { removed += process_phantom_refs_work(_discoveredPhantomRefs[i], is_alive, keep_alive, complete_gc); } phase_times->add_ref_cleared(REF_PHANTOM, removed); } 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. Thread* thr = Thread::current(); id = thr->as_Worker_thread()->id(); } else { // single-threaded discovery, we save in round-robin // fashion to each of the lists. if (_processing_is_mt) { id = next_id(); } } assert(id < _max_num_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 = NULL; switch (rt) { case REF_OTHER: // Unknown reference type, no special treatment break; case REF_SOFT: list = &_discoveredSoftRefs[id]; break; case REF_WEAK: list = &_discoveredWeakRefs[id]; break; case REF_FINAL: list = &_discoveredFinalRefs[id]; break; case REF_PHANTOM: list = &_discoveredPhantomRefs[id]; break; case REF_NONE: // we should not reach here if we are an InstanceRefKlass default: ShouldNotReachHere(); } log_develop_trace(gc, ref)("Thread %d gets list " INTPTR_FORMAT, id, p2i(list)); return list; } inline void ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& refs_list, oop obj, HeapWord* discovered_addr) { assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller"); // First we must make sure this object is only enqueued once. CAS in a non null // discovered_addr. oop current_head = refs_list.head(); // The last ref must have its discovered field pointing to itself. oop next_discovered = (current_head != NULL) ? current_head : obj; oop retest = HeapAccess::oop_atomic_cmpxchg(next_discovered, discovered_addr, oop(NULL)); if (retest == NULL) { // This thread just won the right to enqueue the object. // We have separate lists for enqueueing, so no synchronization // is necessary. refs_list.set_head(obj); refs_list.inc_length(1); log_develop_trace(gc, ref)("Discovered reference (mt) (" INTPTR_FORMAT ": %s)", p2i(obj), obj->klass()->internal_name()); } else { // If retest was non NULL, another thread beat us to it: // The reference has already been discovered... log_develop_trace(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)", p2i(obj), obj->klass()->internal_name()); } } #ifndef PRODUCT // Non-atomic (i.e. concurrent) discovery might allow us // to observe j.l.References with NULL referents, being those // cleared concurrently by mutators during (or after) discovery. void ReferenceProcessor::verify_referent(oop obj) { bool da = discovery_is_atomic(); oop referent = java_lang_ref_Reference::referent(obj); assert(da ? oopDesc::is_oop(referent) : oopDesc::is_oop_or_null(referent), "Bad referent " INTPTR_FORMAT " found in Reference " INTPTR_FORMAT " during %satomic discovery ", p2i(referent), p2i(obj), da ? "" : "non-"); } #endif bool ReferenceProcessor::is_subject_to_discovery(oop const obj) const { return _is_subject_to_discovery->do_object_b(obj); } // We mention two of several possible choices here: // #0: if the reference object is not in the "originating generation" // (or part of the heap being collected, indicated by our "span" // we don't treat it specially (i.e. we scan it as we would // a normal oop, treating its references as strong references). // This means that references can't be discovered unless their // referent is also in the same span. This is the simplest, // most "local" and most conservative approach, albeit one // that may cause weak references to be enqueued least promptly. // We call this choice the "ReferenceBasedDiscovery" policy. // #1: the reference object may be in any generation (span), but if // the referent is in the generation (span) being currently collected // then we can discover the reference object, provided // the object has not already been discovered by // a different concurrently running collector (as may be the // case, for instance, if the reference object is in CMS and // the referent in DefNewGeneration), and provided the processing // of this reference object by the current collector will // appear atomic to every other collector in the system. // (Thus, for instance, a concurrent collector may not // discover references in other generations even if the // referent is in its own generation). This policy may, // in certain cases, enqueue references somewhat sooner than // might Policy #0 above, but at marginally increased cost // and complexity in processing these references. // We call this choice the "RefeferentBasedDiscovery" policy. bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) { // Make sure we are discovering refs (rather than processing discovered refs). if (!_discovering_refs || !RegisterReferences) { return false; } if ((rt == REF_FINAL) && (java_lang_ref_Reference::next(obj) != NULL)) { // Don't rediscover non-active FinalReferences. return false; } if (RefDiscoveryPolicy == ReferenceBasedDiscovery && !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() != NULL) { verify_referent(obj); if (is_alive_non_header()->do_object_b(java_lang_ref_Reference::referent(obj))) { return false; // referent is reachable } } if (rt == REF_SOFT) { // For soft refs we can decide now if these are not // current candidates for clearing, in which case we // can mark through them now, rather than delaying that // to the reference-processing phase. Since all current // time-stamp policies advance the soft-ref clock only // at a 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 != NULL) { // The reference has already been discovered... log_develop_trace(gc, ref)("Already discovered reference (" INTPTR_FORMAT ": %s)", p2i(obj), obj->klass()->internal_name()); if (RefDiscoveryPolicy == ReferentBasedDiscovery) { // assumes that an object is not processed twice; // if it's been already discovered it must be on another // generation's discovered list; so we won't discover it. return false; } else { assert(RefDiscoveryPolicy == ReferenceBasedDiscovery, "Unrecognized policy"); // Check assumption that an object is not potentially // discovered twice except by concurrent collectors that potentially // trace the same Reference object twice. assert(UseConcMarkSweepGC || UseG1GC || UseShenandoahGC, "Only possible with a concurrent marking collector"); return true; } } if (RefDiscoveryPolicy == ReferentBasedDiscovery) { verify_referent(obj); // Discover if and only if EITHER: // .. reference is in our span, OR // .. we are an atomic collector and referent is in our span if (is_subject_to_discovery(obj) || (discovery_is_atomic() && is_subject_to_discovery(java_lang_ref_Reference::referent(obj)))) { } else { return false; } } else { assert(RefDiscoveryPolicy == ReferenceBasedDiscovery && is_subject_to_discovery(obj), "code inconsistency"); } // Get the right type of discovered queue head. DiscoveredList* list = get_discovered_list(rt); if (list == NULL) { return false; // nothing special needs to be done } if (_discovery_is_mt) { add_to_discovered_list_mt(*list, obj, discovered_addr); } else { // We do a raw store here: the field will be visited later when processing // the discovered references. oop current_head = list->head(); // The last ref must have its discovered field pointing to itself. oop next_discovered = (current_head != NULL) ? current_head : obj; assert(discovered == NULL, "control point invariant"); RawAccess<>::oop_store(discovered_addr, next_discovered); list->set_head(obj); list->inc_length(1); log_develop_trace(gc, ref)("Discovered reference (" INTPTR_FORMAT ": %s)", p2i(obj), obj->klass()->internal_name()); } assert(oopDesc::is_oop(obj), "Discovered a bad reference"); verify_referent(obj); return true; } bool ReferenceProcessor::has_discovered_references() { for (uint i = 0; i < _max_num_queues * number_of_subclasses_of_ref(); i++) { if (!_discovered_refs[i].is_empty()) { return true; } } return false; } void ReferenceProcessor::preclean_discovered_references(BoolObjectClosure* is_alive, OopClosure* keep_alive, VoidClosure* complete_gc, 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, keep_alive, complete_gc, 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, keep_alive, complete_gc, 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, keep_alive, complete_gc, 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, keep_alive, complete_gc, yield)) { log_reflist("PhantomRef abort: ", _discoveredPhantomRefs, _max_num_queues); return; } } log_reflist("PhantomRef after: ", _discoveredPhantomRefs, _max_num_queues); } } // Walk the given discovered ref list, and remove all reference objects // whose referents are still alive, whose referents are NULL or which // are not active (have a non-NULL next field). NOTE: When we are // thus precleaning the ref lists (which happens single-threaded today), // we do not disable refs discovery to honor the correct semantics of // java.lang.Reference. As a result, we need to be careful below // that ref removal steps interleave safely with ref discovery steps // (in this thread). bool ReferenceProcessor::preclean_discovered_reflist(DiscoveredList& refs_list, BoolObjectClosure* is_alive, OopClosure* keep_alive, VoidClosure* complete_gc, YieldClosure* yield) { DiscoveredListIterator iter(refs_list, keep_alive, is_alive); while (iter.has_next()) { if (yield->should_return_fine_grain()) { return true; } iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); if (iter.referent() == NULL || iter.is_referent_alive()) { // The referent has been cleared, or is alive; we need to trace // and mark its cohort. log_develop_trace(gc, ref)("Precleaning Reference (" INTPTR_FORMAT ": %s)", p2i(iter.obj()), iter.obj()->klass()->internal_name()); // Remove Reference object from list iter.remove(); // Keep alive its cohort. iter.make_referent_alive(); iter.move_to_next(); } else { iter.next(); } } // Close the reachable set complete_gc->do_void(); if (iter.processed() > 0) { log_develop_trace(gc, ref)(" Dropped " SIZE_FORMAT " Refs out of " SIZE_FORMAT " Refs in discovered list " INTPTR_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 NULL; } 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 either of those cases could produce large amounts of work. return (phase == ReferenceProcessor::RefPhase1 || phase == ReferenceProcessor::RefPhase3); } RefProcMTDegreeAdjuster::RefProcMTDegreeAdjuster(ReferenceProcessor* rp, RefProcPhases phase, size_t ref_count): _rp(rp), _saved_mt_processing(_rp->processing_is_mt()), _saved_num_queues(_rp->num_queues()) { if (!_rp->processing_is_mt() || !_rp->adjust_no_of_processing_threads() || (ReferencesPerThread == 0)) { return; } uint workers = ergo_proc_thread_count(ref_count, _rp->num_queues(), phase); _rp->set_mt_processing(workers > 1); _rp->set_active_mt_degree(workers); } RefProcMTDegreeAdjuster::~RefProcMTDegreeAdjuster() { // Revert to previous status. _rp->set_mt_processing(_saved_mt_processing); _rp->set_active_mt_degree(_saved_num_queues); }