jdk8-mips64-public/hotspot: src/share/vm/memory/referenceProcessor.cpp@c2bf0120ee5d (annotated)

src/share/vm/memory/referenceProcessor.cpp@c2bf0120ee5d (annotated)

src/share/vm/memory/referenceProcessor.cpp

Thu, 01 Sep 2011 16:18:17 +0200

author: stefank
date: Thu, 01 Sep 2011 16:18:17 +0200
changeset 3115: c2bf0120ee5d
parent 2651: 92da084fefc9
child 3117: eca1193ca245
permissions: -rw-r--r--

7085906: Replace the permgen allocated sentinelRef with a self-looped end
Summary: Remove the sentinelRef and let the last Reference in a discovered chain point back to itself.
Reviewed-by: ysr, jmasa

 /*
  * Copyright (c) 2001, 2011, 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.hpp"
 #include "classfile/systemDictionary.hpp"
 #include "gc_interface/collectedHeap.hpp"
 #include "gc_interface/collectedHeap.inline.hpp"
 #include "memory/referencePolicy.hpp"
 #include "memory/referenceProcessor.hpp"
 #include "oops/oop.inline.hpp"
 #include "runtime/java.hpp"
 #include "runtime/jniHandles.hpp"
 ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL;
 ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy      = NULL;
 const int        subclasses_of_ref                = REF_PHANTOM - REF_OTHER;
 // List of discovered references.
 class DiscoveredList {
 public:
   DiscoveredList() : _len(0), _compressed_head(0), _oop_head(NULL) { }
   oop head() const     {
      return UseCompressedOops ?  oopDesc::decode_heap_oop(_compressed_head) :
                                 _oop_head;
   }
   HeapWord* adr_head() {
     return UseCompressedOops ? (HeapWord*)&_compressed_head :
                                (HeapWord*)&_oop_head;
   }
   void   set_head(oop o) {
     if (UseCompressedOops) {
       // Must compress the head ptr.
       _compressed_head = oopDesc::encode_heap_oop(o);
     } else {
       _oop_head = o;
     }
   }
   bool   empty() const          { return head() == NULL; }
   size_t length()               { return _len; }
   void   set_length(size_t len) { _len = len;  }
   void   inc_length(size_t inc) { _len += inc; assert(_len > 0, "Error"); }
   void   dec_length(size_t dec) { _len -= dec; }
 private:
   // Set value depending on UseCompressedOops. This could be a template class
   // but then we have to fix all the instantiations and declarations that use this class.
   oop       _oop_head;
   narrowOop _compressed_head;
   size_t _len;
 };
 void referenceProcessor_init() {
   ReferenceProcessor::init_statics();
 }
 void ReferenceProcessor::init_statics() {
   // Initialize the master soft ref clock.
   java_lang_ref_SoftReference::set_clock(os::javaTimeMillis());
   _always_clear_soft_ref_policy = new AlwaysClearPolicy();
   _default_soft_ref_policy      = new COMPILER2_PRESENT(LRUMaxHeapPolicy())
                                       NOT_COMPILER2(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,
             "Unrecongnized RefDiscoveryPolicy");
 }
 ReferenceProcessor::ReferenceProcessor(MemRegion span,
                                        bool      mt_processing,
                                        int       mt_processing_degree,
                                        bool      mt_discovery,
                                        int       mt_discovery_degree,
                                        bool      atomic_discovery,
                                        BoolObjectClosure* is_alive_non_header,
                                        bool      discovered_list_needs_barrier)  :
   _discovering_refs(false),
   _enqueuing_is_done(false),
   _is_alive_non_header(is_alive_non_header),
   _discovered_list_needs_barrier(discovered_list_needs_barrier),
   _bs(NULL),
   _processing_is_mt(mt_processing),
   _next_id(0)
 {
   _span = span;
   _discovery_is_atomic = atomic_discovery;
   _discovery_is_mt     = mt_discovery;
   _num_q               = MAX2(1, mt_processing_degree);
   _max_num_q           = MAX2(_num_q, mt_discovery_degree);
   _discoveredSoftRefs  = NEW_C_HEAP_ARRAY(DiscoveredList, _max_num_q * subclasses_of_ref);
   if (_discoveredSoftRefs == NULL) {
     vm_exit_during_initialization("Could not allocated RefProc Array");
   }
   _discoveredWeakRefs    = &_discoveredSoftRefs[_max_num_q];
   _discoveredFinalRefs   = &_discoveredWeakRefs[_max_num_q];
   _discoveredPhantomRefs = &_discoveredFinalRefs[_max_num_q];
   // Initialized all entries to NULL
   for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) {
     _discoveredSoftRefs[i].set_head(NULL);
     _discoveredSoftRefs[i].set_length(0);
   }
   // If we do barreirs, cache a copy of the barrier set.
   if (discovered_list_needs_barrier) {
     _bs = Universe::heap()->barrier_set();
   }
   setup_policy(false /* default soft ref policy */);
 }
 #ifndef PRODUCT
 void ReferenceProcessor::verify_no_references_recorded() {
   guarantee(!_discovering_refs, "Discovering refs?");
   for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) {
     guarantee(_discoveredSoftRefs[i].empty(),
               "Found non-empty discovered list");
   }
 }
 #endif
 void ReferenceProcessor::weak_oops_do(OopClosure* f) {
   // Should this instead be
   // for (int i = 0; i < subclasses_of_ref; i++_ {
   //   for (int j = 0; j < _num_q; j++) {
   //     int index = i * _max_num_q + j;
   for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) {
     if (UseCompressedOops) {
       f->do_oop((narrowOop*)_discoveredSoftRefs[i].adr_head());
     } else {
       f->do_oop((oop*)_discoveredSoftRefs[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.
   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(
   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, _current_soft_ref_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.
 uint ReferenceProcessor::count_jni_refs() {
   class AlwaysAliveClosure: public BoolObjectClosure {
   public:
     virtual bool do_object_b(oop obj) { return true; }
     virtual 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++; }
     void do_oop(narrowOop* unused) { ShouldNotReachHere(); }
     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);
   complete_gc->do_void();
 }
 template <class T>
 bool enqueue_discovered_ref_helper(ReferenceProcessor* ref,
                                    AbstractRefProcTaskExecutor* task_executor) {
   // Remember old value of pending references list
   T* pending_list_addr = (T*)java_lang_ref_Reference::pending_list_addr();
   T old_pending_list_value = *pending_list_addr;
   // Enqueue references that are not made active again, and
   // clear the decks for the next collection (cycle).
   ref->enqueue_discovered_reflists((HeapWord*)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, oopDesc::load_decode_heap_oop(pending_list_addr));
   // Stop treating discovered references specially.
   ref->disable_discovery();
   // Return true if new pending references were added
   return old_pending_list_value != *pending_list_addr;
 }
 bool ReferenceProcessor::enqueue_discovered_references(AbstractRefProcTaskExecutor* task_executor) {
   NOT_PRODUCT(verify_ok_to_handle_reflists());
   if (UseCompressedOops) {
     return enqueue_discovered_ref_helper<narrowOop>(this, task_executor);
   } else {
     return enqueue_discovered_ref_helper<oop>(this, task_executor);
   }
 }
 void ReferenceProcessor::enqueue_discovered_reflist(DiscoveredList& refs_list,
                                                     HeapWord* 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 = NULL;
   oop next = refs_list.head();
   // Walk down the list, copying the discovered field into
   // the next field and clearing it.
   while (obj != next) {
     obj = next;
     assert(obj->is_instanceRef(), "should be reference object");
     next = java_lang_ref_Reference::discovered(obj);
     if (TraceReferenceGC && PrintGCDetails) {
       gclog_or_tty->print_cr("        obj " INTPTR_FORMAT "/next " INTPTR_FORMAT,
                              obj, next);
     }
     assert(java_lang_ref_Reference::next(obj) == NULL,
            "The reference should not be enqueued");
     if (next == obj) {  // 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 = oopDesc::atomic_exchange_oop(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);
   }
 }
 // Parallel enqueue task
 class RefProcEnqueueTask: public AbstractRefProcTaskExecutor::EnqueueTask {
 public:
   RefProcEnqueueTask(ReferenceProcessor& ref_processor,
                      DiscoveredList      discovered_refs[],
                      HeapWord*           pending_list_addr,
                      int                 n_queues)
     : EnqueueTask(ref_processor, discovered_refs,
                   pending_list_addr, n_queues)
   { }
   virtual void work(unsigned int work_id) {
     assert(work_id < (unsigned int)_ref_processor.max_num_q(), "Index out-of-bounds");
     // Simplest first cut: static partitioning.
     int index = work_id;
     // The increment on "index" must correspond to the maximum number of queues
     // (n_queues) with which that ReferenceProcessor was created.  That
     // is because of the "clever" way the discovered references lists were
     // allocated and are indexed into.
     assert(_n_queues == (int) _ref_processor.max_num_q(), "Different number not expected");
     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(NULL);
       _refs_lists[index].set_length(0);
     }
   }
 };
 // Enqueue references that are not made active again
 void ReferenceProcessor::enqueue_discovered_reflists(HeapWord* pending_list_addr,
   AbstractRefProcTaskExecutor* task_executor) {
   if (_processing_is_mt && task_executor != NULL) {
     // Parallel code
     RefProcEnqueueTask tsk(*this, _discoveredSoftRefs,
                            pending_list_addr, _max_num_q);
     task_executor->execute(tsk);
   } else {
     // Serial code: call the parent class's implementation
     for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) {
       enqueue_discovered_reflist(_discoveredSoftRefs[i], pending_list_addr);
       _discoveredSoftRefs[i].set_head(NULL);
       _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 _ref != NULL; }
   // 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
   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() {
     if (UseCompressedOops) {
       _keep_alive->do_oop((narrowOop*)_referent_addr);
     } else {
       _keep_alive->do_oop((oop*)_referent_addr);
     }
   }
   // Update the discovered field.
   inline void update_discovered() {
     // First _prev_next ref actually points into DiscoveredList (gross).
     if (UseCompressedOops) {
       if (!oopDesc::is_null(*(narrowOop*)_prev_next)) {
         _keep_alive->do_oop((narrowOop*)_prev_next);
       }
     } else {
       if (!oopDesc::is_null(*(oop*)_prev_next)) {
         _keep_alive->do_oop((oop*)_prev_next);
       }
     }
   }
   // NULL out referent pointer.
   inline void clear_referent() { oop_store_raw(_referent_addr, NULL); }
   // Statistics
   NOT_PRODUCT(
   inline size_t processed() const { return _processed; }
   inline size_t removed() const   { return _removed; }
   )
   inline void move_to_next();
 private:
   DiscoveredList&    _refs_list;
   HeapWord*          _prev_next;
   oop                _prev;
   oop                _ref;
   HeapWord*          _discovered_addr;
   oop                _next;
   HeapWord*          _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.adr_head()),
     _prev(NULL),
     _ref(refs_list.head()),
 #ifdef ASSERT
     _first_seen(refs_list.head()),
 #endif
 #ifndef PRODUCT
     _processed(0),
     _removed(0),
 #endif
     _next(NULL),
     _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);
   oop discovered = java_lang_ref_Reference::discovered(_ref);
   assert(_discovered_addr && discovered->is_oop_or_null(),
          "discovered field is bad");
   _next = discovered;
   _referent_addr = java_lang_ref_Reference::referent_addr(_ref);
   _referent = java_lang_ref_Reference::referent(_ref);
   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;
   _prev = _ref;
   move_to_next();
 }
 inline void DiscoveredListIterator::remove() {
   assert(_ref->is_oop(), "Dropping a bad reference");
   oop_store_raw(_discovered_addr, NULL);
   // First _prev_next ref actually points into DiscoveredList (gross).
   oop new_next;
   if (_next == _ref) {
     // 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;
   } else {
     new_next = _next;
   }
   if (UseCompressedOops) {
     // Remove Reference object from list.
     oopDesc::encode_store_heap_oop((narrowOop*)_prev_next, new_next);
   } else {
     // Remove Reference object from list.
     oopDesc::store_heap_oop((oop*)_prev_next, new_next);
   }
   NOT_PRODUCT(_removed++);
   _refs_list.dec_length(1);
 }
 inline void DiscoveredListIterator::move_to_next() {
   if (_ref == _next) {
     // End of the list.
     _ref = NULL;
   } else {
     _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,
                                    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())) {
       if (TraceReferenceGC) {
         gclog_or_tty->print_cr("Dropping reference (" INTPTR_FORMAT ": %s"  ") by policy",
                                iter.obj(), iter.obj()->blueprint()->internal_name());
       }
       // Remove Reference object from list
       iter.remove();
       // Make the Reference object active again
       iter.make_active();
       // keep the referent around
       iter.make_referent_alive();
       iter.move_to_next();
     } else {
       iter.next();
     }
   }
   // Close the reachable set
   complete_gc->do_void();
   NOT_PRODUCT(
     if (PrintGCDetails && TraceReferenceGC) {
       gclog_or_tty->print_cr(" Dropped %d dead Refs out of %d "
         "discovered Refs by policy  list " INTPTR_FORMAT,
         iter.removed(), iter.processed(), (address)refs_list.head());
     }
   )
 }
 // 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,
                              BoolObjectClosure* is_alive,
                              OopClosure*        keep_alive) {
   assert(discovery_is_atomic(), "Error");
   DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
   while (iter.has_next()) {
     iter.load_ptrs(DEBUG_ONLY(false /* allow_null_referent */));
     DEBUG_ONLY(oop next = java_lang_ref_Reference::next(iter.obj());)
     assert(next == 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)",
                                iter.obj(), iter.obj()->blueprint()->internal_name());
       }
       // The referent is reachable after all.
       // Remove Reference object from list.
       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 {
       iter.next();
     }
   }
   NOT_PRODUCT(
     if (PrintGCDetails && TraceReferenceGC && (iter.processed() > 0)) {
       gclog_or_tty->print_cr(" Dropped %d active Refs out of %d "
         "Refs in discovered list " INTPTR_FORMAT,
         iter.removed(), iter.processed(), (address)refs_list.head());
     }
   )
 }
 void
 ReferenceProcessor::pp2_work_concurrent_discovery(DiscoveredList&    refs_list,
                                                   BoolObjectClosure* is_alive,
                                                   OopClosure*        keep_alive,
                                                   VoidClosure*       complete_gc) {
   assert(!discovery_is_atomic(), "Error");
   DiscoveredListIterator iter(refs_list, keep_alive, is_alive);
   while (iter.has_next()) {
     iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
     HeapWord* next_addr = java_lang_ref_Reference::next_addr(iter.obj());
     oop next = java_lang_ref_Reference::next(iter.obj());
     if ((iter.referent() == NULL || iter.is_referent_alive() ||
          next != NULL)) {
       assert(next->is_oop_or_null(), "bad next field");
       // Remove Reference object from list
       iter.remove();
       // Trace the cohorts
       iter.make_referent_alive();
       if (UseCompressedOops) {
         keep_alive->do_oop((narrowOop*)next_addr);
       } else {
         keep_alive->do_oop((oop*)next_addr);
       }
       iter.move_to_next();
     } else {
       iter.next();
     }
   }
   // Now close the newly reachable set
   complete_gc->do_void();
   NOT_PRODUCT(
     if (PrintGCDetails && TraceReferenceGC && (iter.processed() > 0)) {
       gclog_or_tty->print_cr(" Dropped %d active Refs out of %d "
         "Refs in discovered list " INTPTR_FORMAT,
         iter.removed(), iter.processed(), (address)refs_list.head());
     }
   )
 }
 // Traverse the list and process the referents, by either
 // clearing them or keeping them (and their reachable
 // closure) alive.
 void
 ReferenceProcessor::process_phase3(DiscoveredList&    refs_list,
                                    bool               clear_referent,
                                    BoolObjectClosure* is_alive,
                                    OopClosure*        keep_alive,
                                    VoidClosure*       complete_gc) {
   ResourceMark rm;
   DiscoveredListIterator iter(refs_list, 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 " : "",
                              iter.obj(), iter.obj()->blueprint()->internal_name());
     }
     assert(iter.obj()->is_oop(UseConcMarkSweepGC), "Adding a bad reference");
     iter.next();
   }
   // Remember to update the next pointer of the last ref.
   iter.update_discovered();
   // Close the reachable set
   complete_gc->do_void();
 }
 void
 ReferenceProcessor::clear_discovered_references(DiscoveredList& refs_list) {
   oop obj = NULL;
   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, NULL);
   }
   refs_list.set_head(NULL);
   refs_list.set_length(0);
 }
 void
 ReferenceProcessor::abandon_partial_discovered_list(DiscoveredList& refs_list) {
   clear_discovered_references(refs_list);
 }
 void ReferenceProcessor::abandon_partial_discovery() {
   // loop over the lists
   for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) {
     if (TraceReferenceGC && PrintGCDetails && ((i % _max_num_q) == 0)) {
       gclog_or_tty->print_cr("\nAbandoning %s discovered list",
                              list_name(i));
     }
     abandon_partial_discovered_list(_discoveredSoftRefs[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)
   {
     Thread* thr = Thread::current();
     int refs_list_index = ((WorkerThread*)thr)->id();
     _ref_processor.process_phase1(_refs_lists[refs_list_index], _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)
   {
     // Don't use "refs_list_index" calculated in this way because
     // balance_queues() has moved the Ref's into the first n queues.
     // Thread* thr = Thread::current();
     // int refs_list_index = ((WorkerThread*)thr)->id();
     // _ref_processor.process_phase3(_refs_lists[refs_list_index], _clear_referent,
     _ref_processor.process_phase3(_refs_lists[i], _clear_referent,
                                   &is_alive, &keep_alive, &complete_gc);
   }
 private:
   bool _clear_referent;
 };
 // 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;
   if (TraceReferenceGC && PrintGCDetails) {
     gclog_or_tty->print_cr("\nBalance ref_lists ");
   }
   for (int i = 0; i < _max_num_q; ++i) {
     total_refs += ref_lists[i].length();
     if (TraceReferenceGC && PrintGCDetails) {
       gclog_or_tty->print("%d ", ref_lists[i].length());
     }
   }
   if (TraceReferenceGC && PrintGCDetails) {
     gclog_or_tty->print_cr(" = %d", total_refs);
   }
   size_t avg_refs = total_refs / _num_q + 1;
   int to_idx = 0;
   for (int from_idx = 0; from_idx < _max_num_q; from_idx++) {
     bool move_all = false;
     if (from_idx >= _num_q) {
       move_all = ref_lists[from_idx].length() > 0;
     }
     while ((ref_lists[from_idx].length() > avg_refs) ||
            move_all) {
       assert(to_idx < _num_q, "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(move_tail, move_tail);
         } else {
           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].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(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_q;
       }
     }
   }
 #ifdef ASSERT
   size_t balanced_total_refs = 0;
   for (int i = 0; i < _max_num_q; ++i) {
     balanced_total_refs += ref_lists[i].length();
     if (TraceReferenceGC && PrintGCDetails) {
       gclog_or_tty->print("%d ", ref_lists[i].length());
     }
   }
   if (TraceReferenceGC && PrintGCDetails) {
     gclog_or_tty->print_cr(" = %d", balanced_total_refs);
     gclog_or_tty->flush();
   }
   assert(total_refs == balanced_total_refs, "Balancing was incomplete");
 #endif
 }
 void ReferenceProcessor::balance_all_queues() {
   balance_queues(_discoveredSoftRefs);
   balance_queues(_discoveredWeakRefs);
   balance_queues(_discoveredFinalRefs);
   balance_queues(_discoveredPhantomRefs);
 }
 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_processing = task_executor != NULL && _processing_is_mt;
   // If discovery used MT and a dynamic number of GC threads, then
   // the queues must be balanced for correctness if fewer than the
   // maximum number of queues were used.  The number of queue used
   // during discovery may be different than the number to be used
   // for processing so don't depend of _num_q < _max_num_q as part
   // of the test.
   bool must_balance = _discovery_is_mt;
   if ((mt_processing && ParallelRefProcBalancingEnabled) ||
       must_balance) {
     balance_queues(refs_lists);
   }
   if (PrintReferenceGC && PrintGCDetails) {
     size_t total = 0;
     for (int i = 0; i < _max_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_processing) {
       RefProcPhase1Task phase1(*this, refs_lists, policy, true /*marks_oops_alive*/);
       task_executor->execute(phase1);
     } else {
       for (int i = 0; i < _max_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_processing) {
     RefProcPhase2Task phase2(*this, refs_lists, !discovery_is_atomic() /*marks_oops_alive*/);
     task_executor->execute(phase2);
   } else {
     for (int i = 0; i < _max_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_processing) {
     RefProcPhase3Task phase3(*this, refs_lists, clear_referent, true /*marks_oops_alive*/);
     task_executor->execute(phase3);
   } else {
     for (int i = 0; i < _max_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
   // Should this instead be
   // for (int i = 0; i < subclasses_of_ref; i++_ {
   //   for (int j = 0; j < _num_q; j++) {
   //     int index = i * _max_num_q + j;
   for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) {
     if (TraceReferenceGC && PrintGCDetails && ((i % _max_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);
   while (iter.has_next()) {
     iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
     oop next = java_lang_ref_Reference::next(iter.obj());
     assert(next->is_oop_or_null(), "bad next field");
     // If referent has been cleared or Reference is not active,
     // drop it.
     if (iter.referent() == NULL || next != 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,
             iter.obj(), next, iter.referent());
         }
       )
       // Remove Reference object from list
       iter.remove();
       iter.move_to_next();
     } else {
       iter.next();
     }
   }
   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();
     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(0 <= id && id < _max_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();
   }
   if (TraceReferenceGC && PrintGCDetails) {
     gclog_or_tty->print_cr("Thread %d gets list " INTPTR_FORMAT, id, 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;
   // Note: In the case of G1, this specific pre-barrier is strictly
   // not necessary because the only case we are interested in
   // here is when *discovered_addr is NULL (see the CAS further below),
   // so this will expand to nothing. As a result, we have manually
   // elided this out for G1, but left in the test for some future
   // collector that might have need for a pre-barrier here.
   if (_discovered_list_needs_barrier && !UseG1GC) {
     if (UseCompressedOops) {
       _bs->write_ref_field_pre((narrowOop*)discovered_addr, next_discovered);
     } else {
       _bs->write_ref_field_pre((oop*)discovered_addr, next_discovered);
     }
     guarantee(false, "Need to check non-G1 collector");
   }
   oop retest = oopDesc::atomic_compare_exchange_oop(next_discovered, 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.
     refs_list.set_head(obj);
     refs_list.inc_length(1);
     if (_discovered_list_needs_barrier) {
       _bs->write_ref_field((void*)discovered_addr, next_discovered);
     }
     if (TraceReferenceGC) {
       gclog_or_tty->print_cr("Enqueued reference (mt) (" INTPTR_FORMAT ": %s)",
                              obj, obj->blueprint()->internal_name());
     }
   } 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());
     }
   }
 }
 #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 ? referent->is_oop() : referent->is_oop_or_null(),
          err_msg("Bad referent " INTPTR_FORMAT " found in Reference "
                  INTPTR_FORMAT " during %satomic discovery ",
                  (intptr_t)referent, (intptr_t)obj, da ? "" : "non-"));
 }
 #endif
 // 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 = java_lang_ref_Reference::next(obj);
   if (next != 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) {
     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 major collection cycle, this is always currently
     // accurate.
     if (!_current_soft_ref_policy->should_clear_reference(obj)) {
       return false;
     }
   }
   HeapWord* const discovered_addr = java_lang_ref_Reference::discovered_addr(obj);
   const oop  discovered = java_lang_ref_Reference::discovered(obj);
   assert(discovered->is_oop_or_null(), "bad discovered field");
   if (discovered != NULL) {
     // The reference has already been discovered...
     if (TraceReferenceGC) {
       gclog_or_tty->print_cr("Already enqueued reference (" INTPTR_FORMAT ": %s)",
                              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 || UseG1GC,
              "Only possible with a concurrent marking collector");
       return true;
     }
   }
   if (RefDiscoveryPolicy == ReferentBasedDiscovery) {
     verify_referent(obj);
     // 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(java_lang_ref_Reference::referent(obj)))) {
       // 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
   }
   if (_discovery_is_mt) {
     add_to_discovered_list_mt(*list, obj, discovered_addr);
   } else {
     // If "_discovered_list_needs_barrier", we do write barriers when
     // updating the discovered reference list.  Otherwise, 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;
     // As in the case further above, since we are over-writing a NULL
     // pre-value, we can safely elide the pre-barrier here for the case of G1.
     assert(discovered == NULL, "control point invariant");
     if (_discovered_list_needs_barrier && !UseG1GC) { // safe to elide for G1
       if (UseCompressedOops) {
         _bs->write_ref_field_pre((narrowOop*)discovered_addr, next_discovered);
       } else {
         _bs->write_ref_field_pre((oop*)discovered_addr, next_discovered);
       }
       guarantee(false, "Need to check non-G1 collector");
     }
     oop_store_raw(discovered_addr, next_discovered);
     if (_discovered_list_needs_barrier) {
       _bs->write_ref_field((void*)discovered_addr, next_discovered);
     }
     list->set_head(obj);
     list->inc_length(1);
     if (TraceReferenceGC) {
       gclog_or_tty->print_cr("Enqueued reference (" INTPTR_FORMAT ": %s)",
                                 obj, obj->blueprint()->internal_name());
     }
   }
   assert(obj->is_oop(), "Enqueued a bad reference");
   verify_referent(obj);
   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,
   bool should_unload_classes) {
   NOT_PRODUCT(verify_ok_to_handle_reflists());
 #ifdef ASSERT
   bool must_remember_klasses = ClassUnloading && !UseConcMarkSweepGC ||
                                CMSClassUnloadingEnabled && UseConcMarkSweepGC ||
                                ExplicitGCInvokesConcurrentAndUnloadsClasses &&
                                  UseConcMarkSweepGC && should_unload_classes;
   RememberKlassesChecker mx(must_remember_klasses);
 #endif
   // Soft references
   {
     TraceTime tt("Preclean SoftReferences", PrintGCDetails && PrintReferenceGC,
               false, gclog_or_tty);
     for (int i = 0; i < _max_num_q; i++) {
       if (yield->should_return()) {
         return;
       }
       preclean_discovered_reflist(_discoveredSoftRefs[i], is_alive,
                                   keep_alive, complete_gc, yield);
     }
   }
   // Weak references
   {
     TraceTime tt("Preclean WeakReferences", PrintGCDetails && PrintReferenceGC,
               false, gclog_or_tty);
     for (int i = 0; i < _max_num_q; i++) {
       if (yield->should_return()) {
         return;
       }
       preclean_discovered_reflist(_discoveredWeakRefs[i], is_alive,
                                   keep_alive, complete_gc, yield);
     }
   }
   // Final references
   {
     TraceTime tt("Preclean FinalReferences", PrintGCDetails && PrintReferenceGC,
               false, gclog_or_tty);
     for (int i = 0; i < _max_num_q; i++) {
       if (yield->should_return()) {
         return;
       }
       preclean_discovered_reflist(_discoveredFinalRefs[i], is_alive,
                                   keep_alive, complete_gc, yield);
     }
   }
   // Phantom references
   {
     TraceTime tt("Preclean PhantomReferences", PrintGCDetails && PrintReferenceGC,
               false, gclog_or_tty);
     for (int i = 0; i < _max_num_q; i++) {
       if (yield->should_return()) {
         return;
       }
       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: When we are
 // thus precleaning the ref lists (which happens single-threaded today),
 // we do not disable refs discovery to honour 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).
 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);
   while (iter.has_next()) {
     iter.load_ptrs(DEBUG_ONLY(true /* allow_null_referent */));
     oop obj = iter.obj();
     oop next = java_lang_ref_Reference::next(obj);
     if (iter.referent() == NULL || iter.is_referent_alive() ||
         next != 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();
       // Keep alive its cohort.
       iter.make_referent_alive();
       if (UseCompressedOops) {
         narrowOop* next_addr = (narrowOop*)java_lang_ref_Reference::next_addr(obj);
         keep_alive->do_oop(next_addr);
       } else {
         oop* next_addr = (oop*)java_lang_ref_Reference::next_addr(obj);
         keep_alive->do_oop(next_addr);
       }
       iter.move_to_next();
     } else {
       iter.next();
     }
   }
   // Close the reachable set
   complete_gc->do_void();
   NOT_PRODUCT(
     if (PrintGCDetails && PrintReferenceGC && (iter.processed() > 0)) {
       gclog_or_tty->print_cr(" Dropped %d Refs out of %d "
         "Refs in discovered list " INTPTR_FORMAT,
         iter.removed(), iter.processed(), (address)refs_list.head());
     }
   )
 }
 const char* ReferenceProcessor::list_name(int i) {
    assert(i >= 0 && i <= _max_num_q * subclasses_of_ref, "Out of bounds index");
    int j = i / _max_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
 #ifndef PRODUCT
 void ReferenceProcessor::clear_discovered_references() {
   guarantee(!_discovering_refs, "Discovering refs?");
   for (int i = 0; i < _max_num_q * subclasses_of_ref; i++) {
     clear_discovered_references(_discoveredSoftRefs[i]);
   }
 }
 #endif // PRODUCT

Mercurial > jdk8-mips64-public > hotspot / annotate

src/share/vm/memory/referenceProcessor.cpp@c2bf0120ee5d (annotated)

src/share/vm/memory/referenceProcessor.cpp