Mercurial > hg > truffle
diff src/share/vm/memory/referenceProcessor.cpp @ 0:a61af66fc99e jdk7-b24
Initial load
author | duke |
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date | Sat, 01 Dec 2007 00:00:00 +0000 |
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children | f21b879b4c72 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/share/vm/memory/referenceProcessor.cpp Sat Dec 01 00:00:00 2007 +0000 @@ -0,0 +1,1261 @@ +/* + * Copyright 2001-2007 Sun Microsystems, Inc. All Rights Reserved. + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. + * + * This code is free software; you can redistribute it and/or modify it + * under the terms of the GNU General Public License version 2 only, as + * published by the Free Software Foundation. + * + * This code is distributed in the hope that it will be useful, but WITHOUT + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License + * version 2 for more details (a copy is included in the LICENSE file that + * accompanied this code). + * + * You should have received a copy of the GNU General Public License version + * 2 along with this work; if not, write to the Free Software Foundation, + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. + * + * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, + * CA 95054 USA or visit www.sun.com if you need additional information or + * have any questions. + * + */ + +# include "incls/_precompiled.incl" +# include "incls/_referenceProcessor.cpp.incl" + +// List of discovered references. +class DiscoveredList { +public: + DiscoveredList() : _head(NULL), _len(0) { } + oop head() const { return _head; } + oop* head_ptr() { return &_head; } + void set_head(oop o) { _head = o; } + bool empty() const { return _head == ReferenceProcessor::_sentinelRef; } + size_t length() { return _len; } + void set_length(size_t len) { _len = len; } +private: + size_t _len; + oop _head; +}; + +oop ReferenceProcessor::_sentinelRef = NULL; + +const int subclasses_of_ref = REF_PHANTOM - REF_OTHER; + +void referenceProcessor_init() { + ReferenceProcessor::init_statics(); +} + +void ReferenceProcessor::init_statics() { + assert(_sentinelRef == NULL, "should be initialized precsiely once"); + EXCEPTION_MARK; + _sentinelRef = instanceKlass::cast( + SystemDictionary::object_klass())-> + allocate_permanent_instance(THREAD); + + // Initialize the master soft ref clock. + java_lang_ref_SoftReference::set_clock(os::javaTimeMillis()); + + if (HAS_PENDING_EXCEPTION) { + Handle ex(THREAD, PENDING_EXCEPTION); + vm_exit_during_initialization(ex); + } + assert(_sentinelRef != NULL && _sentinelRef->is_oop(), + "Just constructed it!"); + guarantee(RefDiscoveryPolicy == ReferenceBasedDiscovery || + RefDiscoveryPolicy == ReferentBasedDiscovery, + "Unrecongnized RefDiscoveryPolicy"); +} + + +ReferenceProcessor* ReferenceProcessor::create_ref_processor( + MemRegion span, + bool atomic_discovery, + bool mt_discovery, + BoolObjectClosure* is_alive_non_header, + int parallel_gc_threads, + bool mt_processing) +{ + int mt_degree = 1; + if (parallel_gc_threads > 1) { + mt_degree = parallel_gc_threads; + } + ReferenceProcessor* rp = + new ReferenceProcessor(span, atomic_discovery, + mt_discovery, mt_degree, + mt_processing); + if (rp == NULL) { + vm_exit_during_initialization("Could not allocate ReferenceProcessor object"); + } + rp->set_is_alive_non_header(is_alive_non_header); + return rp; +} + + +ReferenceProcessor::ReferenceProcessor(MemRegion span, + bool atomic_discovery, bool mt_discovery, int mt_degree, + bool mt_processing) : + _discovering_refs(false), + _enqueuing_is_done(false), + _is_alive_non_header(NULL), + _processing_is_mt(mt_processing), + _next_id(0) +{ + _span = span; + _discovery_is_atomic = atomic_discovery; + _discovery_is_mt = mt_discovery; + _num_q = mt_degree; + _discoveredSoftRefs = NEW_C_HEAP_ARRAY(DiscoveredList, _num_q * subclasses_of_ref); + if (_discoveredSoftRefs == NULL) { + vm_exit_during_initialization("Could not allocated RefProc Array"); + } + _discoveredWeakRefs = &_discoveredSoftRefs[_num_q]; + _discoveredFinalRefs = &_discoveredWeakRefs[_num_q]; + _discoveredPhantomRefs = &_discoveredFinalRefs[_num_q]; + assert(_sentinelRef != NULL, "_sentinelRef is NULL"); + // Initialized all entries to _sentinelRef + for (int i = 0; i < _num_q * subclasses_of_ref; i++) { + _discoveredSoftRefs[i].set_head(_sentinelRef); + _discoveredSoftRefs[i].set_length(0); + } +} + +#ifndef PRODUCT +void ReferenceProcessor::verify_no_references_recorded() { + guarantee(!_discovering_refs, "Discovering refs?"); + for (int i = 0; i < _num_q * subclasses_of_ref; i++) { + guarantee(_discoveredSoftRefs[i].empty(), + "Found non-empty discovered list"); + } +} +#endif + +void ReferenceProcessor::weak_oops_do(OopClosure* f) { + for (int i = 0; i < _num_q * subclasses_of_ref; i++) { + f->do_oop(_discoveredSoftRefs[i].head_ptr()); + } +} + +void ReferenceProcessor::oops_do(OopClosure* f) { + f->do_oop(&_sentinelRef); +} + +void ReferenceProcessor::update_soft_ref_master_clock() +{ + // Update (advance) the soft ref master clock field. This must be done + // after processing the soft ref list. + jlong now = os::javaTimeMillis(); + jlong clock = java_lang_ref_SoftReference::clock(); + NOT_PRODUCT( + if (now < clock) { + warning("time warp: %d to %d", clock, now); + } + ) + // In product mode, protect ourselves from system time being adjusted + // externally and going backward; see note in the implementation of + // GenCollectedHeap::time_since_last_gc() for the right way to fix + // this uniformly throughout the VM; see bug-id 4741166. XXX + if (now > clock) { + java_lang_ref_SoftReference::set_clock(now); + } + // Else leave clock stalled at its old value until time progresses + // past clock value. +} + + +void +ReferenceProcessor::process_discovered_references( + ReferencePolicy* policy, + BoolObjectClosure* is_alive, + OopClosure* keep_alive, + VoidClosure* complete_gc, + AbstractRefProcTaskExecutor* task_executor) { + NOT_PRODUCT(verify_ok_to_handle_reflists()); + + assert(!enqueuing_is_done(), "If here enqueuing should not be complete"); + // Stop treating discovered references specially. + disable_discovery(); + + bool trace_time = PrintGCDetails && PrintReferenceGC; + // Soft references + { + TraceTime tt("SoftReference", trace_time, false, gclog_or_tty); + process_discovered_reflist(_discoveredSoftRefs, policy, true, + is_alive, keep_alive, complete_gc, task_executor); + } + + update_soft_ref_master_clock(); + + // Weak references + { + TraceTime tt("WeakReference", trace_time, false, gclog_or_tty); + process_discovered_reflist(_discoveredWeakRefs, NULL, true, + is_alive, keep_alive, complete_gc, task_executor); + } + + // Final references + { + TraceTime tt("FinalReference", trace_time, false, gclog_or_tty); + process_discovered_reflist(_discoveredFinalRefs, NULL, false, + is_alive, keep_alive, complete_gc, task_executor); + } + + // Phantom references + { + TraceTime tt("PhantomReference", trace_time, false, gclog_or_tty); + process_discovered_reflist(_discoveredPhantomRefs, NULL, false, + is_alive, keep_alive, complete_gc, task_executor); + } + + // Weak global JNI references. It would make more sense (semantically) to + // traverse these simultaneously with the regular weak references above, but + // that is not how the JDK1.2 specification is. See #4126360. Native code can + // thus use JNI weak references to circumvent the phantom references and + // resurrect a "post-mortem" object. + { + TraceTime tt("JNI Weak Reference", trace_time, false, gclog_or_tty); + if (task_executor != NULL) { + task_executor->set_single_threaded_mode(); + } + process_phaseJNI(is_alive, keep_alive, complete_gc); + } +} + + +#ifndef PRODUCT +// Calculate the number of jni handles. +unsigned int ReferenceProcessor::count_jni_refs() +{ + class AlwaysAliveClosure: public BoolObjectClosure { + public: + bool do_object_b(oop obj) { return true; } + void do_object(oop obj) { assert(false, "Don't call"); } + }; + + class CountHandleClosure: public OopClosure { + private: + int _count; + public: + CountHandleClosure(): _count(0) {} + void do_oop(oop* unused) { + _count++; + } + int count() { return _count; } + }; + CountHandleClosure global_handle_count; + AlwaysAliveClosure always_alive; + JNIHandles::weak_oops_do(&always_alive, &global_handle_count); + return global_handle_count.count(); +} +#endif + +void ReferenceProcessor::process_phaseJNI(BoolObjectClosure* is_alive, + OopClosure* keep_alive, + VoidClosure* complete_gc) { +#ifndef PRODUCT + if (PrintGCDetails && PrintReferenceGC) { + unsigned int count = count_jni_refs(); + gclog_or_tty->print(", %u refs", count); + } +#endif + JNIHandles::weak_oops_do(is_alive, keep_alive); + // Finally remember to keep sentinel around + keep_alive->do_oop(&_sentinelRef); + complete_gc->do_void(); +} + +bool ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor) { + NOT_PRODUCT(verify_ok_to_handle_reflists()); + // Remember old value of pending references list + oop* pending_list_addr = java_lang_ref_Reference::pending_list_addr(); + oop old_pending_list_value = *pending_list_addr; + + // Enqueue references that are not made active again, and + // clear the decks for the next collection (cycle). + enqueue_discovered_reflists(pending_list_addr, task_executor); + // Do the oop-check on pending_list_addr missed in + // enqueue_discovered_reflist. We should probably + // do a raw oop_check so that future such idempotent + // oop_stores relying on the oop-check side-effect + // may be elided automatically and safely without + // affecting correctness. + oop_store(pending_list_addr, *(pending_list_addr)); + + // Stop treating discovered references specially. + disable_discovery(); + + // Return true if new pending references were added + return old_pending_list_value != *pending_list_addr; +} + +void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list, + oop* pending_list_addr) { + // Given a list of refs linked through the "discovered" field + // (java.lang.ref.Reference.discovered) chain them through the + // "next" field (java.lang.ref.Reference.next) and prepend + // to the pending list. + if (TraceReferenceGC && PrintGCDetails) { + gclog_or_tty->print_cr("ReferenceProcessor::enqueue_discovered_reflist list " + INTPTR_FORMAT, (address)refs_list.head()); + } + oop obj = refs_list.head(); + // Walk down the list, copying the discovered field into + // the next field and clearing it (except for the last + // non-sentinel object which is treated specially to avoid + // confusion with an active reference). + while (obj != _sentinelRef) { + assert(obj->is_instanceRef(), "should be reference object"); + oop next = java_lang_ref_Reference::discovered(obj); + if (TraceReferenceGC && PrintGCDetails) { + gclog_or_tty->print_cr(" obj " INTPTR_FORMAT "/next " INTPTR_FORMAT, + (oopDesc*) obj, (oopDesc*) next); + } + assert(*java_lang_ref_Reference::next_addr(obj) == NULL, + "The reference should not be enqueued"); + if (next == _sentinelRef) { // obj is last + // Swap refs_list into pendling_list_addr and + // set obj's next to what we read from pending_list_addr. + oop old = (oop)Atomic::xchg_ptr(refs_list.head(), pending_list_addr); + // Need oop_check on pending_list_addr above; + // see special oop-check code at the end of + // enqueue_discovered_reflists() further below. + if (old == NULL) { + // obj should be made to point to itself, since + // pending list was empty. + java_lang_ref_Reference::set_next(obj, obj); + } else { + java_lang_ref_Reference::set_next(obj, old); + } + } else { + java_lang_ref_Reference::set_next(obj, next); + } + java_lang_ref_Reference::set_discovered(obj, (oop) NULL); + obj = next; + } +} + +// Parallel enqueue task +class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask { +public: + RefProcEnqueueTask(ReferenceProcessor& ref_processor, + DiscoveredList discovered_refs[], + oop* pending_list_addr, + oop sentinel_ref, + int n_queues) + : EnqueueTask(ref_processor, discovered_refs, + pending_list_addr, sentinel_ref, n_queues) + { } + + virtual void work(unsigned int work_id) + { + assert(work_id < (unsigned int)_ref_processor.num_q(), "Index out-of-bounds"); + // Simplest first cut: static partitioning. + int index = work_id; + for (int j = 0; j < subclasses_of_ref; j++, index += _n_queues) { + _ref_processor.enqueue_discovered_reflist( + _refs_lists[index], _pending_list_addr); + _refs_lists[index].set_head(_sentinel_ref); + _refs_lists[index].set_length(0); + } + } +}; + +// Enqueue references that are not made active again +void ReferenceProcessor::enqueue_discovered_reflists(oop* pending_list_addr, + AbstractRefProcTaskExecutor* task_executor) { + if (_processing_is_mt && task_executor != NULL) { + // Parallel code + RefProcEnqueueTask tsk(*this, _discoveredSoftRefs, + pending_list_addr, _sentinelRef, _num_q); + task_executor->execute(tsk); + } else { + // Serial code: call the parent class's implementation + for (int i = 0; i < _num_q * subclasses_of_ref; i++) { + enqueue_discovered_reflist(_discoveredSoftRefs[i], pending_list_addr); + _discoveredSoftRefs[i].set_head(_sentinelRef); + _discoveredSoftRefs[i].set_length(0); + } + } +} + +// Iterator for the list of discovered references. +class DiscoveredListIterator { +public: + inline DiscoveredListIterator(DiscoveredList& refs_list, + OopClosure* keep_alive, + BoolObjectClosure* is_alive); + + // End Of List. + inline bool has_next() const + { return _next != ReferenceProcessor::_sentinelRef; } + + // Get oop to the Reference object. + inline oop obj() const { return _ref; } + + // Get oop to the referent object. + inline oop referent() const { return _referent; } + + // Returns true if referent is alive. + inline bool is_referent_alive() const; + + // Loads data for the current reference. + // The "allow_null_referent" argument tells us to allow for the possibility + // of a NULL referent in the discovered Reference object. This typically + // happens in the case of concurrent collectors that may have done the + // discovery concurrently or interleaved with mutator execution. + inline void load_ptrs(DEBUG_ONLY(bool allow_null_referent)); + + // Move to the next discovered reference. + inline void next(); + + // Remove the current reference from the list and move to the next. + inline void remove(); + + // Make the Reference object active again. + inline void make_active() { java_lang_ref_Reference::set_next(_ref, NULL); } + + // Make the referent alive. + inline void make_referent_alive() { _keep_alive->do_oop(_referent_addr); } + + // Update the discovered field. + inline void update_discovered() { _keep_alive->do_oop(_prev_next); } + + // NULL out referent pointer. + inline void clear_referent() { *_referent_addr = NULL; } + + // Statistics + NOT_PRODUCT( + inline size_t processed() const { return _processed; } + inline size_t removed() const { return _removed; } + ) + +private: + inline void move_to_next(); + +private: + DiscoveredList& _refs_list; + oop* _prev_next; + oop _ref; + oop* _discovered_addr; + oop _next; + oop* _referent_addr; + oop _referent; + OopClosure* _keep_alive; + BoolObjectClosure* _is_alive; + DEBUG_ONLY( + oop _first_seen; // cyclic linked list check + ) + NOT_PRODUCT( + size_t _processed; + size_t _removed; + ) +}; + +inline DiscoveredListIterator::DiscoveredListIterator(DiscoveredList& refs_list, + OopClosure* keep_alive, + BoolObjectClosure* is_alive) + : _refs_list(refs_list), + _prev_next(refs_list.head_ptr()), + _ref(refs_list.head()), +#ifdef ASSERT + _first_seen(refs_list.head()), +#endif +#ifndef PRODUCT + _processed(0), + _removed(0), +#endif + _next(refs_list.head()), + _keep_alive(keep_alive), + _is_alive(is_alive) +{ } + +inline bool DiscoveredListIterator::is_referent_alive() const +{ + return _is_alive->do_object_b(_referent); +} + +inline void DiscoveredListIterator::load_ptrs(DEBUG_ONLY(bool allow_null_referent)) +{ + _discovered_addr = java_lang_ref_Reference::discovered_addr(_ref); + assert(_discovered_addr && (*_discovered_addr)->is_oop_or_null(), + "discovered field is bad"); + _next = *_discovered_addr; + _referent_addr = java_lang_ref_Reference::referent_addr(_ref); + _referent = *_referent_addr; + assert(Universe::heap()->is_in_reserved_or_null(_referent), + "Wrong oop found in java.lang.Reference object"); + assert(allow_null_referent ? + _referent->is_oop_or_null() + : _referent->is_oop(), + "bad referent"); +} + +inline void DiscoveredListIterator::next() +{ + _prev_next = _discovered_addr; + move_to_next(); +} + +inline void DiscoveredListIterator::remove() +{ + assert(_ref->is_oop(), "Dropping a bad reference"); + // Clear the discovered_addr field so that the object does + // not look like it has been discovered. + *_discovered_addr = NULL; + // Remove Reference object from list. + *_prev_next = _next; + NOT_PRODUCT(_removed++); + move_to_next(); +} + +inline void DiscoveredListIterator::move_to_next() +{ + _ref = _next; + assert(_ref != _first_seen, "cyclic ref_list found"); + NOT_PRODUCT(_processed++); +} + + +// NOTE: process_phase*() are largely similar, and at a high level +// merely iterate over the extant list applying a predicate to +// each of its elements and possibly removing that element from the +// list and applying some further closures to that element. +// We should consider the possibility of replacing these +// process_phase*() methods by abstracting them into +// a single general iterator invocation that receives appropriate +// closures that accomplish this work. + +// (SoftReferences only) Traverse the list and remove any SoftReferences whose +// referents are not alive, but that should be kept alive for policy reasons. +// Keep alive the transitive closure of all such referents. +void +ReferenceProcessor::process_phase1(DiscoveredList& refs_list_addr, + ReferencePolicy* policy, + BoolObjectClosure* is_alive, + OopClosure* keep_alive, + VoidClosure* complete_gc) { + assert(policy != NULL, "Must have a non-NULL policy"); + DiscoveredListIterator iter(refs_list_addr, keep_alive, is_alive); + // Decide which softly reachable refs should be kept alive. + while (iter.has_next()) { + iter.load_ptrs(DEBUG_ONLY(!discovery_is_atomic() /* allow_null_referent */)); + bool referent_is_dead = (iter.referent() != NULL) && !iter.is_referent_alive(); + if (referent_is_dead && !policy->should_clear_reference(iter.obj())) { + if (TraceReferenceGC) { + gclog_or_tty->print_cr("Dropping reference (" INTPTR_FORMAT ": %s" ") by policy", + (address)iter.obj(), iter.obj()->blueprint()->internal_name()); + } + // Make the Reference object active again + iter.make_active(); + // keep the referent around + iter.make_referent_alive(); + // Remove Reference object from list + iter.remove(); + } else { + iter.next(); + } + } + // Close the reachable set + complete_gc->do_void(); + NOT_PRODUCT( + if (PrintGCDetails && TraceReferenceGC) { + gclog_or_tty->print(" Dropped %d dead Refs out of %d " + "discovered Refs by policy ", iter.removed(), iter.processed()); + } + ) +} + +// Traverse the list and remove any Refs that are not active, or +// whose referents are either alive or NULL. +void +ReferenceProcessor::pp2_work(DiscoveredList& refs_list_addr, + BoolObjectClosure* is_alive, + OopClosure* keep_alive) +{ + assert(discovery_is_atomic(), "Error"); + DiscoveredListIterator iter(refs_list_addr, keep_alive, is_alive); + while (iter.has_next()) { + iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); + DEBUG_ONLY(oop* next_addr = java_lang_ref_Reference::next_addr(iter.obj());) + assert(*next_addr == NULL, "Should not discover inactive Reference"); + if (iter.is_referent_alive()) { + if (TraceReferenceGC) { + gclog_or_tty->print_cr("Dropping strongly reachable reference (" INTPTR_FORMAT ": %s)", + (address)iter.obj(), iter.obj()->blueprint()->internal_name()); + } + // The referent is reachable after all. + // Update the referent pointer as necessary: Note that this + // should not entail any recursive marking because the + // referent must already have been traversed. + iter.make_referent_alive(); + // Remove Reference object from list + iter.remove(); + } else { + iter.next(); + } + } + NOT_PRODUCT( + if (PrintGCDetails && TraceReferenceGC) { + gclog_or_tty->print(" Dropped %d active Refs out of %d " + "Refs in discovered list ", iter.removed(), iter.processed()); + } + ) +} + +void +ReferenceProcessor::pp2_work_concurrent_discovery( + DiscoveredList& refs_list_addr, + BoolObjectClosure* is_alive, + OopClosure* keep_alive, + VoidClosure* complete_gc) +{ + assert(!discovery_is_atomic(), "Error"); + DiscoveredListIterator iter(refs_list_addr, keep_alive, is_alive); + while (iter.has_next()) { + iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); + oop* next_addr = java_lang_ref_Reference::next_addr(iter.obj()); + if ((iter.referent() == NULL || iter.is_referent_alive() || + *next_addr != NULL)) { + assert((*next_addr)->is_oop_or_null(), "bad next field"); + // Remove Reference object from list + iter.remove(); + // Trace the cohorts + iter.make_referent_alive(); + keep_alive->do_oop(next_addr); + } else { + iter.next(); + } + } + // Now close the newly reachable set + complete_gc->do_void(); + NOT_PRODUCT( + if (PrintGCDetails && TraceReferenceGC) { + gclog_or_tty->print(" Dropped %d active Refs out of %d " + "Refs in discovered list ", iter.removed(), iter.processed()); + } + ) +} + +// Traverse the list and process the referents, by either +// either clearing them or keeping them (and their reachable +// closure) alive. +void +ReferenceProcessor::process_phase3(DiscoveredList& refs_list_addr, + bool clear_referent, + BoolObjectClosure* is_alive, + OopClosure* keep_alive, + VoidClosure* complete_gc) { + DiscoveredListIterator iter(refs_list_addr, keep_alive, is_alive); + while (iter.has_next()) { + iter.update_discovered(); + iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */)); + if (clear_referent) { + // NULL out referent pointer + iter.clear_referent(); + } else { + // keep the referent around + iter.make_referent_alive(); + } + if (TraceReferenceGC) { + gclog_or_tty->print_cr("Adding %sreference (" INTPTR_FORMAT ": %s) as pending", + clear_referent ? "cleared " : "", + (address)iter.obj(), iter.obj()->blueprint()->internal_name()); + } + assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference"); + // If discovery is concurrent, we may have objects with null referents, + // being those that were concurrently cleared after they were discovered + // (and not subsequently precleaned). + assert( (discovery_is_atomic() && iter.referent()->is_oop()) + || (!discovery_is_atomic() && iter.referent()->is_oop_or_null(UseConcMarkSweepGC)), + "Adding a bad referent"); + iter.next(); + } + // Remember to keep sentinel pointer around + iter.update_discovered(); + // Close the reachable set + complete_gc->do_void(); +} + +void +ReferenceProcessor::abandon_partial_discovered_list(DiscoveredList& ref_list) { + oop obj = ref_list.head(); + while (obj != _sentinelRef) { + oop* discovered_addr = java_lang_ref_Reference::discovered_addr(obj); + obj = *discovered_addr; + *discovered_addr = NULL; + } + ref_list.set_head(_sentinelRef); + ref_list.set_length(0); +} + +void +ReferenceProcessor::abandon_partial_discovered_list_arr(DiscoveredList refs_lists[]) { + for (int i = 0; i < _num_q; i++) { + abandon_partial_discovered_list(refs_lists[i]); + } +} + +class RefProcPhase1Task: public AbstractRefProcTaskExecutor::ProcessTask { +public: + RefProcPhase1Task(ReferenceProcessor& ref_processor, + DiscoveredList refs_lists[], + ReferencePolicy* policy, + bool marks_oops_alive) + : ProcessTask(ref_processor, refs_lists, marks_oops_alive), + _policy(policy) + { } + virtual void work(unsigned int i, BoolObjectClosure& is_alive, + OopClosure& keep_alive, + VoidClosure& complete_gc) + { + _ref_processor.process_phase1(_refs_lists[i], _policy, + &is_alive, &keep_alive, &complete_gc); + } +private: + ReferencePolicy* _policy; +}; + +class RefProcPhase2Task: public AbstractRefProcTaskExecutor::ProcessTask { +public: + RefProcPhase2Task(ReferenceProcessor& ref_processor, + DiscoveredList refs_lists[], + bool marks_oops_alive) + : ProcessTask(ref_processor, refs_lists, marks_oops_alive) + { } + virtual void work(unsigned int i, BoolObjectClosure& is_alive, + OopClosure& keep_alive, + VoidClosure& complete_gc) + { + _ref_processor.process_phase2(_refs_lists[i], + &is_alive, &keep_alive, &complete_gc); + } +}; + +class RefProcPhase3Task: public AbstractRefProcTaskExecutor::ProcessTask { +public: + RefProcPhase3Task(ReferenceProcessor& ref_processor, + DiscoveredList refs_lists[], + bool clear_referent, + bool marks_oops_alive) + : ProcessTask(ref_processor, refs_lists, marks_oops_alive), + _clear_referent(clear_referent) + { } + virtual void work(unsigned int i, BoolObjectClosure& is_alive, + OopClosure& keep_alive, + VoidClosure& complete_gc) + { + _ref_processor.process_phase3(_refs_lists[i], _clear_referent, + &is_alive, &keep_alive, &complete_gc); + } +private: + bool _clear_referent; +}; + +// Balances reference queues. +void ReferenceProcessor::balance_queues(DiscoveredList ref_lists[]) +{ + // calculate total length + size_t total_refs = 0; + for (int i = 0; i < _num_q; ++i) { + total_refs += ref_lists[i].length(); + } + size_t avg_refs = total_refs / _num_q + 1; + int to_idx = 0; + for (int from_idx = 0; from_idx < _num_q; from_idx++) { + while (ref_lists[from_idx].length() > avg_refs) { + assert(to_idx < _num_q, "Sanity Check!"); + if (ref_lists[to_idx].length() < avg_refs) { + // move superfluous refs + size_t refs_to_move = + MIN2(ref_lists[from_idx].length() - avg_refs, + avg_refs - ref_lists[to_idx].length()); + oop move_head = ref_lists[from_idx].head(); + oop move_tail = move_head; + oop new_head = move_head; + // find an element to split the list on + for (size_t j = 0; j < refs_to_move; ++j) { + move_tail = new_head; + new_head = *java_lang_ref_Reference::discovered_addr(new_head); + } + java_lang_ref_Reference::set_discovered(move_tail, ref_lists[to_idx].head()); + ref_lists[to_idx].set_head(move_head); + ref_lists[to_idx].set_length(ref_lists[to_idx].length() + refs_to_move); + ref_lists[from_idx].set_head(new_head); + ref_lists[from_idx].set_length(ref_lists[from_idx].length() - refs_to_move); + } else { + ++to_idx; + } + } + } +} + +void +ReferenceProcessor::process_discovered_reflist( + DiscoveredList refs_lists[], + ReferencePolicy* policy, + bool clear_referent, + BoolObjectClosure* is_alive, + OopClosure* keep_alive, + VoidClosure* complete_gc, + AbstractRefProcTaskExecutor* task_executor) +{ + bool mt = task_executor != NULL && _processing_is_mt; + if (mt && ParallelRefProcBalancingEnabled) { + balance_queues(refs_lists); + } + if (PrintReferenceGC && PrintGCDetails) { + size_t total = 0; + for (int i = 0; i < _num_q; ++i) { + total += refs_lists[i].length(); + } + gclog_or_tty->print(", %u refs", total); + } + + // Phase 1 (soft refs only): + // . Traverse the list and remove any SoftReferences whose + // referents are not alive, but that should be kept alive for + // policy reasons. Keep alive the transitive closure of all + // such referents. + if (policy != NULL) { + if (mt) { + RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/); + task_executor->execute(phase1); + } else { + for (int i = 0; i < _num_q; i++) { + process_phase1(refs_lists[i], policy, + is_alive, keep_alive, complete_gc); + } + } + } else { // policy == NULL + assert(refs_lists != _discoveredSoftRefs, + "Policy must be specified for soft references."); + } + + // Phase 2: + // . Traverse the list and remove any refs whose referents are alive. + if (mt) { + RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/); + task_executor->execute(phase2); + } else { + for (int i = 0; i < _num_q; i++) { + process_phase2(refs_lists[i], is_alive, keep_alive, complete_gc); + } + } + + // Phase 3: + // . Traverse the list and process referents as appropriate. + if (mt) { + RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/); + task_executor->execute(phase3); + } else { + for (int i = 0; i < _num_q; i++) { + process_phase3(refs_lists[i], clear_referent, + is_alive, keep_alive, complete_gc); + } + } +} + +void ReferenceProcessor::clean_up_discovered_references() { + // loop over the lists + for (int i = 0; i < _num_q * subclasses_of_ref; i++) { + if (TraceReferenceGC && PrintGCDetails && ((i % _num_q) == 0)) { + gclog_or_tty->print_cr( + "\nScrubbing %s discovered list of Null referents", + list_name(i)); + } + clean_up_discovered_reflist(_discoveredSoftRefs[i]); + } +} + +void ReferenceProcessor::clean_up_discovered_reflist(DiscoveredList& refs_list) { + assert(!discovery_is_atomic(), "Else why call this method?"); + DiscoveredListIterator iter(refs_list, NULL, NULL); + size_t length = refs_list.length(); + while (iter.has_next()) { + iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); + oop* next_addr = java_lang_ref_Reference::next_addr(iter.obj()); + assert((*next_addr)->is_oop_or_null(), "bad next field"); + // If referent has been cleared or Reference is not active, + // drop it. + if (iter.referent() == NULL || *next_addr != NULL) { + debug_only( + if (PrintGCDetails && TraceReferenceGC) { + gclog_or_tty->print_cr("clean_up_discovered_list: Dropping Reference: " + INTPTR_FORMAT " with next field: " INTPTR_FORMAT + " and referent: " INTPTR_FORMAT, + (address)iter.obj(), (address)*next_addr, (address)iter.referent()); + } + ) + // Remove Reference object from list + iter.remove(); + --length; + } else { + iter.next(); + } + } + refs_list.set_length(length); + NOT_PRODUCT( + if (PrintGCDetails && TraceReferenceGC) { + gclog_or_tty->print( + " Removed %d Refs with NULL referents out of %d discovered Refs", + iter.removed(), iter.processed()); + } + ) +} + +inline DiscoveredList* ReferenceProcessor::get_discovered_list(ReferenceType rt) { + int id = 0; + // Determine the queue index to use for this object. + if (_discovery_is_mt) { + // During a multi-threaded discovery phase, + // each thread saves to its "own" list. + Thread* thr = Thread::current(); + assert(thr->is_GC_task_thread(), + "Dubious cast from Thread* to WorkerThread*?"); + id = ((WorkerThread*)thr)->id(); + } else { + // single-threaded discovery, we save in round-robin + // fashion to each of the lists. + if (_processing_is_mt) { + id = next_id(); + } + } + assert(0 <= id && id < _num_q, "Id is out-of-bounds (call Freud?)"); + + // Get the discovered queue to which we will add + DiscoveredList* list = NULL; + switch (rt) { + case REF_OTHER: + // Unknown reference type, no special treatment + break; + case REF_SOFT: + list = &_discoveredSoftRefs[id]; + break; + case REF_WEAK: + list = &_discoveredWeakRefs[id]; + break; + case REF_FINAL: + list = &_discoveredFinalRefs[id]; + break; + case REF_PHANTOM: + list = &_discoveredPhantomRefs[id]; + break; + case REF_NONE: + // we should not reach here if we are an instanceRefKlass + default: + ShouldNotReachHere(); + } + return list; +} + +inline void ReferenceProcessor::add_to_discovered_list_mt(DiscoveredList& list, + oop obj, oop* discovered_addr) { + assert(_discovery_is_mt, "!_discovery_is_mt should have been handled by caller"); + // First we must make sure this object is only enqueued once. CAS in a non null + // discovered_addr. + oop retest = (oop)Atomic::cmpxchg_ptr(list.head(), discovered_addr, NULL); + if (retest == NULL) { + // This thread just won the right to enqueue the object. + // We have separate lists for enqueueing so no synchronization + // is necessary. + list.set_head(obj); + list.set_length(list.length() + 1); + } else { + // If retest was non NULL, another thread beat us to it: + // The reference has already been discovered... + if (TraceReferenceGC) { + gclog_or_tty->print_cr("Already enqueued reference (" INTPTR_FORMAT ": %s)", + obj, obj->blueprint()->internal_name()); + } + } +} + + +// We mention two of several possible choices here: +// #0: if the reference object is not in the "originating generation" +// (or part of the heap being collected, indicated by our "span" +// we don't treat it specially (i.e. we scan it as we would +// a normal oop, treating its references as strong references). +// This means that references can't be enqueued unless their +// referent is also in the same span. This is the simplest, +// most "local" and most conservative approach, albeit one +// that may cause weak references to be enqueued least promptly. +// We call this choice the "ReferenceBasedDiscovery" policy. +// #1: the reference object may be in any generation (span), but if +// the referent is in the generation (span) being currently collected +// then we can discover the reference object, provided +// the object has not already been discovered by +// a different concurrently running collector (as may be the +// case, for instance, if the reference object is in CMS and +// the referent in DefNewGeneration), and provided the processing +// of this reference object by the current collector will +// appear atomic to every other collector in the system. +// (Thus, for instance, a concurrent collector may not +// discover references in other generations even if the +// referent is in its own generation). This policy may, +// in certain cases, enqueue references somewhat sooner than +// might Policy #0 above, but at marginally increased cost +// and complexity in processing these references. +// We call this choice the "RefeferentBasedDiscovery" policy. +bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) { + // We enqueue references only if we are discovering refs + // (rather than processing discovered refs). + if (!_discovering_refs || !RegisterReferences) { + return false; + } + // We only enqueue active references. + oop* next_addr = java_lang_ref_Reference::next_addr(obj); + if (*next_addr != NULL) { + return false; + } + + HeapWord* obj_addr = (HeapWord*)obj; + if (RefDiscoveryPolicy == ReferenceBasedDiscovery && + !_span.contains(obj_addr)) { + // Reference is not in the originating generation; + // don't treat it specially (i.e. we want to scan it as a normal + // object with strong references). + return false; + } + + // We only enqueue references whose referents are not (yet) strongly + // reachable. + if (is_alive_non_header() != NULL) { + oop referent = java_lang_ref_Reference::referent(obj); + // We'd like to assert the following: + // assert(referent != NULL, "Refs with null referents already filtered"); + // However, since this code may be executed concurrently with + // mutators, which can clear() the referent, it is not + // guaranteed that the referent is non-NULL. + if (is_alive_non_header()->do_object_b(referent)) { + return false; // referent is reachable + } + } + + oop* discovered_addr = java_lang_ref_Reference::discovered_addr(obj); + assert(discovered_addr != NULL && (*discovered_addr)->is_oop_or_null(), + "bad discovered field"); + if (*discovered_addr != NULL) { + // The reference has already been discovered... + if (TraceReferenceGC) { + gclog_or_tty->print_cr("Already enqueued reference (" INTPTR_FORMAT ": %s)", + (oopDesc*)obj, obj->blueprint()->internal_name()); + } + if (RefDiscoveryPolicy == ReferentBasedDiscovery) { + // assumes that an object is not processed twice; + // if it's been already discovered it must be on another + // generation's discovered list; so we won't discover it. + return false; + } else { + assert(RefDiscoveryPolicy == ReferenceBasedDiscovery, + "Unrecognized policy"); + // Check assumption that an object is not potentially + // discovered twice except by concurrent collectors that potentially + // trace the same Reference object twice. + assert(UseConcMarkSweepGC, + "Only possible with a concurrent collector"); + return true; + } + } + + if (RefDiscoveryPolicy == ReferentBasedDiscovery) { + oop referent = java_lang_ref_Reference::referent(obj); + assert(referent->is_oop(), "bad referent"); + // enqueue if and only if either: + // reference is in our span or + // we are an atomic collector and referent is in our span + if (_span.contains(obj_addr) || + (discovery_is_atomic() && _span.contains(referent))) { + // should_enqueue = true; + } else { + return false; + } + } else { + assert(RefDiscoveryPolicy == ReferenceBasedDiscovery && + _span.contains(obj_addr), "code inconsistency"); + } + + // Get the right type of discovered queue head. + DiscoveredList* list = get_discovered_list(rt); + if (list == NULL) { + return false; // nothing special needs to be done + } + + // We do a raw store here, the field will be visited later when + // processing the discovered references. + if (_discovery_is_mt) { + add_to_discovered_list_mt(*list, obj, discovered_addr); + } else { + *discovered_addr = list->head(); + list->set_head(obj); + list->set_length(list->length() + 1); + } + + // In the MT discovery case, it is currently possible to see + // the following message multiple times if several threads + // discover a reference about the same time. Only one will + // however have actually added it to the disocvered queue. + // One could let add_to_discovered_list_mt() return an + // indication for success in queueing (by 1 thread) or + // failure (by all other threads), but I decided the extra + // code was not worth the effort for something that is + // only used for debugging support. + if (TraceReferenceGC) { + oop referent = java_lang_ref_Reference::referent(obj); + if (PrintGCDetails) { + gclog_or_tty->print_cr("Enqueued reference (" INTPTR_FORMAT ": %s)", + (oopDesc*) obj, obj->blueprint()->internal_name()); + } + assert(referent->is_oop(), "Enqueued a bad referent"); + } + assert(obj->is_oop(), "Enqueued a bad reference"); + return true; +} + +// Preclean the discovered references by removing those +// whose referents are alive, and by marking from those that +// are not active. These lists can be handled here +// in any order and, indeed, concurrently. +void ReferenceProcessor::preclean_discovered_references( + BoolObjectClosure* is_alive, + OopClosure* keep_alive, + VoidClosure* complete_gc, + YieldClosure* yield) { + + NOT_PRODUCT(verify_ok_to_handle_reflists()); + + // Soft references + { + TraceTime tt("Preclean SoftReferences", PrintGCDetails && PrintReferenceGC, + false, gclog_or_tty); + for (int i = 0; i < _num_q; i++) { + preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive, + keep_alive, complete_gc, yield); + } + } + if (yield->should_return()) { + return; + } + + // Weak references + { + TraceTime tt("Preclean WeakReferences", PrintGCDetails && PrintReferenceGC, + false, gclog_or_tty); + for (int i = 0; i < _num_q; i++) { + preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive, + keep_alive, complete_gc, yield); + } + } + if (yield->should_return()) { + return; + } + + // Final references + { + TraceTime tt("Preclean FinalReferences", PrintGCDetails && PrintReferenceGC, + false, gclog_or_tty); + for (int i = 0; i < _num_q; i++) { + preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive, + keep_alive, complete_gc, yield); + } + } + if (yield->should_return()) { + return; + } + + // Phantom references + { + TraceTime tt("Preclean PhantomReferences", PrintGCDetails && PrintReferenceGC, + false, gclog_or_tty); + for (int i = 0; i < _num_q; i++) { + preclean_discovered_reflist(_discoveredPhantomRefs[i], is_alive, + keep_alive, complete_gc, yield); + } + } +} + +// Walk the given discovered ref list, and remove all reference objects +// whose referents are still alive, whose referents are NULL or which +// are not active (have a non-NULL next field). NOTE: For this to work +// correctly, refs discovery can not be happening concurrently with this +// step. +void ReferenceProcessor::preclean_discovered_reflist( + DiscoveredList& refs_list, BoolObjectClosure* is_alive, + OopClosure* keep_alive, VoidClosure* complete_gc, YieldClosure* yield) { + + DiscoveredListIterator iter(refs_list, keep_alive, is_alive); + size_t length = refs_list.length(); + while (iter.has_next()) { + iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */)); + oop* next_addr = java_lang_ref_Reference::next_addr(iter.obj()); + if (iter.referent() == NULL || iter.is_referent_alive() || + *next_addr != NULL) { + // The referent has been cleared, or is alive, or the Reference is not + // active; we need to trace and mark its cohort. + if (TraceReferenceGC) { + gclog_or_tty->print_cr("Precleaning Reference (" INTPTR_FORMAT ": %s)", + iter.obj(), iter.obj()->blueprint()->internal_name()); + } + // Remove Reference object from list + iter.remove(); + --length; + // Keep alive its cohort. + iter.make_referent_alive(); + keep_alive->do_oop(next_addr); + } else { + iter.next(); + } + } + refs_list.set_length(length); + + // Close the reachable set + complete_gc->do_void(); + + NOT_PRODUCT( + if (PrintGCDetails && PrintReferenceGC) { + gclog_or_tty->print(" Dropped %d Refs out of %d " + "Refs in discovered list ", iter.removed(), iter.processed()); + } + ) +} + +const char* ReferenceProcessor::list_name(int i) { + assert(i >= 0 && i <= _num_q * subclasses_of_ref, "Out of bounds index"); + int j = i / _num_q; + switch (j) { + case 0: return "SoftRef"; + case 1: return "WeakRef"; + case 2: return "FinalRef"; + case 3: return "PhantomRef"; + } + ShouldNotReachHere(); + return NULL; +} + +#ifndef PRODUCT +void ReferenceProcessor::verify_ok_to_handle_reflists() { + // empty for now +} +#endif + +void ReferenceProcessor::verify() { + guarantee(_sentinelRef != NULL && _sentinelRef->is_oop(), "Lost _sentinelRef"); +} + +#ifndef PRODUCT +void ReferenceProcessor::clear_discovered_references() { + guarantee(!_discovering_refs, "Discovering refs?"); + for (int i = 0; i < _num_q * subclasses_of_ref; i++) { + oop obj = _discoveredSoftRefs[i].head(); + while (obj != _sentinelRef) { + oop next = java_lang_ref_Reference::discovered(obj); + java_lang_ref_Reference::set_discovered(obj, (oop) NULL); + obj = next; + } + _discoveredSoftRefs[i].set_head(_sentinelRef); + _discoveredSoftRefs[i].set_length(0); + } +} +#endif // PRODUCT