6684579: SoftReference processing can be made more efficient

Summary: For current soft-ref clearing policies, we can decide at marking time if a soft-reference will definitely not be cleared, postponing the decision of whether it will definitely be cleared to the final reference processing phase. This can be especially beneficial in the case of concurrent collectors where the marking is usually concurrent but reference processing is usually not.
Reviewed-by: jmasa

src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp

@@ -1961,6 +1961,7 @@ void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
 
   ref_processor()->set_enqueuing_is_done(false);
   ref_processor()->enable_discovery();
+  ref_processor()->snap_policy(clear_all_soft_refs);
   // If an asynchronous collection finishes, the _modUnionTable is
   // all clear.  If we are assuming the collection from an asynchronous
   // collection, clear the _modUnionTable.
@@ -2384,6 +2385,9 @@ void CMSCollector::collect_in_foreground(bool clear_all_soft_refs) {
     Universe::verify(true);
   }
 
+  // Snapshot the soft reference policy to be used in this collection cycle.
+  ref_processor()->snap_policy(clear_all_soft_refs);
+
   bool init_mark_was_synchronous = false; // until proven otherwise
   while (_collectorState != Idling) {
     if (TraceCMSState) {
@@ -4591,11 +4595,11 @@ size_t CMSCollector::preclean_mod_union_table(
     if (!dirtyRegion.is_empty()) {
       assert(numDirtyCards > 0, "consistency check");
       HeapWord* stop_point = NULL;
-      {
       stopTimer();
       CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
                                bitMapLock());
       startTimer();
+      {
         verify_work_stacks_empty();
         verify_overflow_empty();
         sample_eden();
@@ -4612,10 +4616,6 @@ size_t CMSCollector::preclean_mod_union_table(
         assert((CMSPermGenPrecleaningEnabled && (gen == _permGen)) ||
                (_collectorState == AbortablePreclean && should_abort_preclean()),
                "Unparsable objects should only be in perm gen.");
-
-        stopTimer();
-        CMSTokenSyncWithLocks ts(true, bitMapLock());
-        startTimer();
         _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
         if (should_abort_preclean()) {
           break; // out of preclean loop
@@ -5678,23 +5678,14 @@ void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
 
   ResourceMark rm;
   HandleMark   hm;
-  ReferencePolicy* soft_ref_policy;
 
-  assert(!ref_processor()->enqueuing_is_done(), "Enqueuing should not be complete");
+  ReferenceProcessor* rp = ref_processor();
+  assert(rp->span().equals(_span), "Spans should be equal");
+  assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
   // Process weak references.
-  if (clear_all_soft_refs) {
-    soft_ref_policy = new AlwaysClearPolicy();
-  } else {
-#ifdef COMPILER2
-    soft_ref_policy = new LRUMaxHeapPolicy();
-#else
-    soft_ref_policy = new LRUCurrentHeapPolicy();
-#endif // COMPILER2
-  }
+  rp->snap_policy(clear_all_soft_refs);
   verify_work_stacks_empty();
 
-  ReferenceProcessor* rp = ref_processor();
-  assert(rp->span().equals(_span), "Spans should be equal");
   CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
                                           &_markStack, false /* !preclean */);
   CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
@@ -5704,14 +5695,12 @@ void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
     TraceTime t("weak refs processing", PrintGCDetails, false, gclog_or_tty);
     if (rp->processing_is_mt()) {
       CMSRefProcTaskExecutor task_executor(*this);
-      rp->process_discovered_references(soft_ref_policy,
-                                        &_is_alive_closure,
+      rp->process_discovered_references(&_is_alive_closure,
                                         &cmsKeepAliveClosure,
                                         &cmsDrainMarkingStackClosure,
                                         &task_executor);
     } else {
-      rp->process_discovered_references(soft_ref_policy,
-                                        &_is_alive_closure,
+      rp->process_discovered_references(&_is_alive_closure,
                                         &cmsKeepAliveClosure,
                                         &cmsDrainMarkingStackClosure,
                                         NULL);

src/share/vm/gc_implementation/g1/concurrentMark.cpp

@@ -811,6 +811,7 @@ void ConcurrentMark::checkpointRootsInitialPost() {
   ReferenceProcessor* rp = g1h->ref_processor();
   rp->verify_no_references_recorded();
   rp->enable_discovery(); // enable ("weak") refs discovery
+  rp->snap_policy(false); // snapshot the soft ref policy to be used in this cycle
 
   SATBMarkQueueSet& satb_mq_set = JavaThread::satb_mark_queue_set();
   satb_mq_set.set_process_completed_threshold(G1SATBProcessCompletedThreshold);
@@ -1829,32 +1830,21 @@ class G1CMDrainMarkingStackClosure: public VoidClosure {
 void ConcurrentMark::weakRefsWork(bool clear_all_soft_refs) {
   ResourceMark rm;
   HandleMark   hm;
-  ReferencePolicy* soft_ref_policy;
+  G1CollectedHeap* g1h   = G1CollectedHeap::heap();
+  ReferenceProcessor* rp = g1h->ref_processor();
 
   // Process weak references.
-  if (clear_all_soft_refs) {
-    soft_ref_policy = new AlwaysClearPolicy();
-  } else {
-#ifdef COMPILER2
-    soft_ref_policy = new LRUMaxHeapPolicy();
-#else
-    soft_ref_policy = new LRUCurrentHeapPolicy();
-#endif
-  }
+  rp->snap_policy(clear_all_soft_refs);
   assert(_markStack.isEmpty(), "mark stack should be empty");
 
-  G1CollectedHeap* g1 = G1CollectedHeap::heap();
-  G1CMIsAliveClosure g1IsAliveClosure(g1);
-
-  G1CMKeepAliveClosure g1KeepAliveClosure(g1, this, nextMarkBitMap());
+  G1CMIsAliveClosure   g1IsAliveClosure  (g1h);
+  G1CMKeepAliveClosure g1KeepAliveClosure(g1h, this, nextMarkBitMap());
   G1CMDrainMarkingStackClosure
     g1DrainMarkingStackClosure(nextMarkBitMap(), &_markStack,
                                &g1KeepAliveClosure);
 
   // XXXYYY  Also: copy the parallel ref processing code from CMS.
-  ReferenceProcessor* rp = g1->ref_processor();
-  rp->process_discovered_references(soft_ref_policy,
-                                    &g1IsAliveClosure,
+  rp->process_discovered_references(&g1IsAliveClosure,
                                     &g1KeepAliveClosure,
                                     &g1DrainMarkingStackClosure,
                                     NULL);

src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp

@@ -891,6 +891,7 @@ void G1CollectedHeap::do_collection(bool full, bool clear_all_soft_refs,
     ReferenceProcessorIsAliveMutator rp_is_alive_null(ref_processor(), NULL);
 
     ref_processor()->enable_discovery();
+    ref_processor()->snap_policy(clear_all_soft_refs);
 
     // Do collection work
     {
@@ -2463,7 +2464,7 @@ G1CollectedHeap::do_collection_pause_at_safepoint(HeapRegion* popular_region) {
 
     COMPILER2_PRESENT(DerivedPointerTable::clear());
 
-    // We want to turn off ref discovere, if necessary, and turn it back on
+    // We want to turn off ref discovery, if necessary, and turn it back on
     // on again later if we do.
     bool was_enabled = ref_processor()->discovery_enabled();
     if (was_enabled) ref_processor()->disable_discovery();

src/share/vm/gc_implementation/g1/g1MarkSweep.cpp

@@ -33,8 +33,9 @@ void G1MarkSweep::invoke_at_safepoint(ReferenceProcessor* rp,
 
   // hook up weak ref data so it can be used during Mark-Sweep
   assert(GenMarkSweep::ref_processor() == NULL, "no stomping");
-  GenMarkSweep::_ref_processor = rp;
   assert(rp != NULL, "should be non-NULL");
+  GenMarkSweep::_ref_processor = rp;
+  rp->snap_policy(clear_all_softrefs);
 
   // When collecting the permanent generation methodOops may be moving,
   // so we either have to flush all bcp data or convert it into bci.
@@ -121,20 +122,9 @@ void G1MarkSweep::mark_sweep_phase1(bool& marked_for_unloading,
                            &GenMarkSweep::follow_root_closure);
 
   // Process reference objects found during marking
-  ReferencePolicy *soft_ref_policy;
-  if (clear_all_softrefs) {
-    soft_ref_policy = new AlwaysClearPolicy();
-  } else {
-#ifdef COMPILER2
-    soft_ref_policy = new LRUMaxHeapPolicy();
-#else
-    soft_ref_policy = new LRUCurrentHeapPolicy();
-#endif
-  }
-  assert(soft_ref_policy != NULL,"No soft reference policy");
-  GenMarkSweep::ref_processor()->process_discovered_references(
-                                   soft_ref_policy,
-                                   &GenMarkSweep::is_alive,
+  ReferenceProcessor* rp = GenMarkSweep::ref_processor();
+  rp->snap_policy(clear_all_softrefs);
+  rp->process_discovered_references(&GenMarkSweep::is_alive,
                                     &GenMarkSweep::keep_alive,
                                     &GenMarkSweep::follow_stack_closure,
                                     NULL);

src/share/vm/gc_implementation/parNew/parNewGeneration.cpp

@@ -759,17 +759,12 @@ void ParNewGeneration::collect(bool   full,
                thread_state_set.steals(),
                thread_state_set.pops()+thread_state_set.steals());
   }
-  assert(thread_state_set.pushes() == thread_state_set.pops() + thread_state_set.steals(),
+  assert(thread_state_set.pushes() == thread_state_set.pops()
+                                    + thread_state_set.steals(),
          "Or else the queues are leaky.");
 
-  // For now, process discovered weak refs sequentially.
-#ifdef COMPILER2
-  ReferencePolicy *soft_ref_policy = new LRUMaxHeapPolicy();
-#else
-  ReferencePolicy *soft_ref_policy = new LRUCurrentHeapPolicy();
-#endif // COMPILER2
-
   // Process (weak) reference objects found during scavenge.
+  ReferenceProcessor* rp = ref_processor();
   IsAliveClosure is_alive(this);
   ScanWeakRefClosure scan_weak_ref(this);
   KeepAliveClosure keep_alive(&scan_weak_ref);
@@ -778,18 +773,17 @@ void ParNewGeneration::collect(bool   full,
   set_promo_failure_scan_stack_closure(&scan_without_gc_barrier);
   EvacuateFollowersClosureGeneral evacuate_followers(gch, _level,
     &scan_without_gc_barrier, &scan_with_gc_barrier);
-  if (ref_processor()->processing_is_mt()) {
+  rp->snap_policy(clear_all_soft_refs);
+  if (rp->processing_is_mt()) {
     ParNewRefProcTaskExecutor task_executor(*this, thread_state_set);
-    ref_processor()->process_discovered_references(
-        soft_ref_policy, &is_alive, &keep_alive, &evacuate_followers,
-        &task_executor);
+    rp->process_discovered_references(&is_alive, &keep_alive,
+                                      &evacuate_followers, &task_executor);
   } else {
     thread_state_set.flush();
     gch->set_par_threads(0);  // 0 ==> non-parallel.
     gch->save_marks();
-    ref_processor()->process_discovered_references(
-      soft_ref_policy, &is_alive, &keep_alive, &evacuate_followers,
-      NULL);
+    rp->process_discovered_references(&is_alive, &keep_alive,
+                                      &evacuate_followers, NULL);
   }
   if (!promotion_failed()) {
     // Swap the survivor spaces.
@@ -851,14 +845,14 @@ void ParNewGeneration::collect(bool   full,
 
   SpecializationStats::print();
 
-  ref_processor()->set_enqueuing_is_done(true);
-  if (ref_processor()->processing_is_mt()) {
+  rp->set_enqueuing_is_done(true);
+  if (rp->processing_is_mt()) {
     ParNewRefProcTaskExecutor task_executor(*this, thread_state_set);
-    ref_processor()->enqueue_discovered_references(&task_executor);
+    rp->enqueue_discovered_references(&task_executor);
   } else {
-    ref_processor()->enqueue_discovered_references(NULL);
+    rp->enqueue_discovered_references(NULL);
   }
-  ref_processor()->verify_no_references_recorded();
+  rp->verify_no_references_recorded();
 }
 
 static int sum;

src/share/vm/gc_implementation/parallelScavenge/psMarkSweep.cpp

@@ -172,6 +172,7 @@ void PSMarkSweep::invoke_no_policy(bool clear_all_softrefs) {
     COMPILER2_PRESENT(DerivedPointerTable::clear());
 
     ref_processor()->enable_discovery();
+    ref_processor()->snap_policy(clear_all_softrefs);
 
     mark_sweep_phase1(clear_all_softrefs);
 
@@ -517,20 +518,9 @@ void PSMarkSweep::mark_sweep_phase1(bool clear_all_softrefs) {
 
   // Process reference objects found during marking
   {
-    ReferencePolicy *soft_ref_policy;
-    if (clear_all_softrefs) {
-      soft_ref_policy = new AlwaysClearPolicy();
-    } else {
-#ifdef COMPILER2
-      soft_ref_policy = new LRUMaxHeapPolicy();
-#else
-      soft_ref_policy = new LRUCurrentHeapPolicy();
-#endif // COMPILER2
-    }
-    assert(soft_ref_policy != NULL,"No soft reference policy");
+    ref_processor()->snap_policy(clear_all_softrefs);
     ref_processor()->process_discovered_references(
-      soft_ref_policy, is_alive_closure(), mark_and_push_closure(),
-      follow_stack_closure(), NULL);
+      is_alive_closure(), mark_and_push_closure(), follow_stack_closure(), NULL);
   }
 
   // Follow system dictionary roots and unload classes

src/share/vm/gc_implementation/parallelScavenge/psParallelCompact.cpp

@@ -1578,6 +1578,7 @@ void PSParallelCompact::invoke_no_policy(bool maximum_heap_compaction) {
     COMPILER2_PRESENT(DerivedPointerTable::clear());
 
     ref_processor()->enable_discovery();
+    ref_processor()->snap_policy(maximum_heap_compaction);
 
     bool marked_for_unloading = false;
 
@@ -1894,26 +1895,14 @@ void PSParallelCompact::marking_phase(ParCompactionManager* cm,
   // Process reference objects found during marking
   {
     TraceTime tm_r("reference processing", print_phases(), true, gclog_or_tty);
-    ReferencePolicy *soft_ref_policy;
-    if (maximum_heap_compaction) {
-      soft_ref_policy = new AlwaysClearPolicy();
-    } else {
-#ifdef COMPILER2
-      soft_ref_policy = new LRUMaxHeapPolicy();
-#else
-      soft_ref_policy = new LRUCurrentHeapPolicy();
-#endif // COMPILER2
-    }
-    assert(soft_ref_policy != NULL, "No soft reference policy");
     if (ref_processor()->processing_is_mt()) {
       RefProcTaskExecutor task_executor;
       ref_processor()->process_discovered_references(
-        soft_ref_policy, is_alive_closure(), &mark_and_push_closure,
-        &follow_stack_closure, &task_executor);
+        is_alive_closure(), &mark_and_push_closure, &follow_stack_closure,
+        &task_executor);
     } else {
       ref_processor()->process_discovered_references(
-        soft_ref_policy, is_alive_closure(), &mark_and_push_closure,
-        &follow_stack_closure, NULL);
+        is_alive_closure(), &mark_and_push_closure, &follow_stack_closure, NULL);
     }
   }
 

src/share/vm/gc_implementation/parallelScavenge/psScavenge.cpp

@@ -330,6 +330,7 @@ bool PSScavenge::invoke_no_policy() {
     COMPILER2_PRESENT(DerivedPointerTable::clear());
 
     reference_processor()->enable_discovery();
+    reference_processor()->snap_policy(false);
 
     // We track how much was promoted to the next generation for
     // the AdaptiveSizePolicy.
@@ -394,24 +395,16 @@ bool PSScavenge::invoke_no_policy() {
 
     // Process reference objects discovered during scavenge
     {
-#ifdef COMPILER2
-      ReferencePolicy *soft_ref_policy = new LRUMaxHeapPolicy();
-#else
-      ReferencePolicy *soft_ref_policy = new LRUCurrentHeapPolicy();
-#endif // COMPILER2
-
+      reference_processor()->snap_policy(false); // not always_clear
       PSKeepAliveClosure keep_alive(promotion_manager);
       PSEvacuateFollowersClosure evac_followers(promotion_manager);
-      assert(soft_ref_policy != NULL,"No soft reference policy");
       if (reference_processor()->processing_is_mt()) {
         PSRefProcTaskExecutor task_executor;
         reference_processor()->process_discovered_references(
-          soft_ref_policy, &_is_alive_closure, &keep_alive, &evac_followers,
-          &task_executor);
+          &_is_alive_closure, &keep_alive, &evac_followers, &task_executor);
       } else {
         reference_processor()->process_discovered_references(
-          soft_ref_policy, &_is_alive_closure, &keep_alive, &evac_followers,
-          NULL);
+          &_is_alive_closure, &keep_alive, &evac_followers, NULL);
       }
     }
 

src/share/vm/includeDB_core

@@ -3434,6 +3434,7 @@ referenceProcessor.cpp                  referenceProcessor.hpp
 referenceProcessor.cpp                  systemDictionary.hpp
 
 referenceProcessor.hpp                  instanceRefKlass.hpp
+referenceProcessor.hpp                  referencePolicy.hpp
 
 reflection.cpp                          arguments.hpp
 reflection.cpp                          handles.inline.hpp

src/share/vm/memory/defNewGeneration.cpp

@@ -540,14 +540,6 @@ void DefNewGeneration::collect(bool   full,
   assert(gch->no_allocs_since_save_marks(0),
          "save marks have not been newly set.");
 
-  // Weak refs.
-  // FIXME: Are these storage leaks, or are they resource objects?
-#ifdef COMPILER2
-  ReferencePolicy *soft_ref_policy = new LRUMaxHeapPolicy();
-#else
-  ReferencePolicy *soft_ref_policy = new LRUCurrentHeapPolicy();
-#endif // COMPILER2
-
   // Not very pretty.
   CollectorPolicy* cp = gch->collector_policy();
 
@@ -574,8 +566,10 @@ void DefNewGeneration::collect(bool   full,
   evacuate_followers.do_void();
 
   FastKeepAliveClosure keep_alive(this, &scan_weak_ref);
-  ref_processor()->process_discovered_references(
-    soft_ref_policy, &is_alive, &keep_alive, &evacuate_followers, NULL);
+  ReferenceProcessor* rp = ref_processor();
+  rp->snap_policy(clear_all_soft_refs);
+  rp->process_discovered_references(&is_alive, &keep_alive, &evacuate_followers,
+                                    NULL);
   if (!promotion_failed()) {
     // Swap the survivor spaces.
     eden()->clear(SpaceDecorator::Mangle);

src/share/vm/memory/genCollectedHeap.cpp

@@ -525,8 +525,9 @@ void GenCollectedHeap::do_collection(bool  full,
           if (rp->discovery_is_atomic()) {
             rp->verify_no_references_recorded();
             rp->enable_discovery();
+            rp->snap_policy(clear_all_soft_refs);
           } else {
-            // collect() will enable discovery as appropriate
+            // collect() below will enable discovery as appropriate
           }
           _gens[i]->collect(full, clear_all_soft_refs, size, is_tlab);
           if (!rp->enqueuing_is_done()) {

src/share/vm/memory/genMarkSweep.cpp

@@ -31,8 +31,9 @@ void GenMarkSweep::invoke_at_safepoint(int level, ReferenceProcessor* rp,
 
   // hook up weak ref data so it can be used during Mark-Sweep
   assert(ref_processor() == NULL, "no stomping");
-  _ref_processor = rp;
   assert(rp != NULL, "should be non-NULL");
+  _ref_processor = rp;
+  rp->snap_policy(clear_all_softrefs);
 
   TraceTime t1("Full GC", PrintGC && !PrintGCDetails, true, gclog_or_tty);
 
@@ -245,20 +246,9 @@ void GenMarkSweep::mark_sweep_phase1(int level,
 
   // Process reference objects found during marking
   {
-    ReferencePolicy *soft_ref_policy;
-    if (clear_all_softrefs) {
-      soft_ref_policy = new AlwaysClearPolicy();
-    } else {
-#ifdef COMPILER2
-      soft_ref_policy = new LRUMaxHeapPolicy();
-#else
-      soft_ref_policy = new LRUCurrentHeapPolicy();
-#endif // COMPILER2
-    }
-    assert(soft_ref_policy != NULL,"No soft reference policy");
+    ref_processor()->snap_policy(clear_all_softrefs);
     ref_processor()->process_discovered_references(
-      soft_ref_policy, &is_alive, &keep_alive,
-      &follow_stack_closure, NULL);
+      &is_alive, &keep_alive, &follow_stack_closure, NULL);
   }
 
   // Follow system dictionary roots and unload classes

src/share/vm/memory/referencePolicy.cpp

@@ -26,6 +26,11 @@
 # include "incls/_referencePolicy.cpp.incl"
 
 LRUCurrentHeapPolicy::LRUCurrentHeapPolicy() {
+  snap();
+}
+
+// Capture state (of-the-VM) information needed to evaluate the policy
+void LRUCurrentHeapPolicy::snap() {
   _max_interval = (Universe::get_heap_free_at_last_gc() / M) * SoftRefLRUPolicyMSPerMB;
   assert(_max_interval >= 0,"Sanity check");
 }
@@ -47,6 +52,11 @@ bool LRUCurrentHeapPolicy::should_clear_reference(oop p) {
 /////////////////////// MaxHeap //////////////////////
 
 LRUMaxHeapPolicy::LRUMaxHeapPolicy() {
+  snap();
+}
+
+// Capture state (of-the-VM) information needed to evaluate the policy
+void LRUMaxHeapPolicy::snap() {
   size_t max_heap = MaxHeapSize;
   max_heap -= Universe::get_heap_used_at_last_gc();
   max_heap /= M;

src/share/vm/memory/referencePolicy.hpp

@@ -26,9 +26,11 @@
 // should be cleared.
 
 
-class ReferencePolicy : public ResourceObj {
+class ReferencePolicy : public CHeapObj {
  public:
   virtual bool should_clear_reference(oop p)       { ShouldNotReachHere(); return true; }
+  // Capture state (of-the-VM) information needed to evaluate the policy
+  virtual void snap() { /* do nothing */ }
 };
 
 class NeverClearPolicy : public ReferencePolicy {
@@ -48,6 +50,8 @@ class LRUCurrentHeapPolicy : public ReferencePolicy {
  public:
   LRUCurrentHeapPolicy();
 
+  // Capture state (of-the-VM) information needed to evaluate the policy
+  void snap();
   bool should_clear_reference(oop p);
 };
 
@@ -58,5 +62,7 @@ class LRUMaxHeapPolicy : public ReferencePolicy {
  public:
   LRUMaxHeapPolicy();
 
+  // Capture state (of-the-VM) information needed to evaluate the policy
+  void snap();
   bool should_clear_reference(oop p);
 };

src/share/vm/memory/referenceProcessor.cpp

@@ -25,6 +25,11 @@
 # include "incls/_precompiled.incl"
 # include "incls/_referenceProcessor.cpp.incl"
 
+ReferencePolicy* ReferenceProcessor::_always_clear_soft_ref_policy = NULL;
+ReferencePolicy* ReferenceProcessor::_default_soft_ref_policy      = NULL;
+oop              ReferenceProcessor::_sentinelRef = NULL;
+const int        subclasses_of_ref                = REF_PHANTOM - REF_OTHER;
+
 // List of discovered references.
 class DiscoveredList {
 public:
@@ -58,10 +63,6 @@ private:
   size_t _len;
 };
 
-oop  ReferenceProcessor::_sentinelRef = NULL;
-
-const int subclasses_of_ref = REF_PHANTOM - REF_OTHER;
-
 void referenceProcessor_init() {
   ReferenceProcessor::init_statics();
 }
@@ -82,6 +83,12 @@ void ReferenceProcessor::init_statics() {
   }
   assert(_sentinelRef != NULL && _sentinelRef->is_oop(),
          "Just constructed it!");
+  _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");
@@ -108,6 +115,7 @@ ReferenceProcessor::create_ref_processor(MemRegion          span,
     vm_exit_during_initialization("Could not allocate ReferenceProcessor object");
   }
   rp->set_is_alive_non_header(is_alive_non_header);
+  rp->snap_policy(false /* default soft ref policy */);
   return rp;
 }
 
@@ -194,7 +202,6 @@ void ReferenceProcessor::update_soft_ref_master_clock() {
 }
 
 void ReferenceProcessor::process_discovered_references(
-  ReferencePolicy*             policy,
   BoolObjectClosure*           is_alive,
   OopClosure*                  keep_alive,
   VoidClosure*                 complete_gc,
@@ -209,7 +216,7 @@ void ReferenceProcessor::process_discovered_references(
   // Soft references
   {
     TraceTime tt("SoftReference", trace_time, false, gclog_or_tty);
-    process_discovered_reflist(_discoveredSoftRefs, policy, true,
+    process_discovered_reflist(_discoveredSoftRefs, _current_soft_ref_policy, true,
                                is_alive, keep_alive, complete_gc, task_executor);
   }
 
@@ -1092,15 +1099,28 @@ bool ReferenceProcessor::discover_reference(oop obj, ReferenceType rt) {
   // 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.
+    // In the case of non-concurrent discovery, the last
+    // disjunct below should hold. It may not hold in the
+    // case of concurrent discovery because mutators may
+    // concurrently clear() a Reference.
+    assert(UseConcMarkSweepGC || UseG1GC || referent != NULL,
+           "Refs with null referents already filtered");
     if (is_alive_non_header()->do_object_b(referent)) {
       return false;  // referent is reachable
     }
   }
+  if (rt == REF_SOFT) {
+    // For soft refs we can decide now if these are not
+    // current candidates for clearing, in which case we
+    // can mark through them now, rather than delaying that
+    // to the reference-processing phase. Since all current
+    // time-stamp policies advance the soft-ref clock only
+    // at a 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);

src/share/vm/memory/referenceProcessor.hpp

@@ -23,7 +23,7 @@
  */
 
 // ReferenceProcessor class encapsulates the per-"collector" processing
-// of "weak" references for GC. The interface is useful for supporting
+// of java.lang.Reference objects for GC. The interface is useful for supporting
 // a generational abstraction, in particular when there are multiple
 // generations that are being independently collected -- possibly
 // concurrently and/or incrementally.  Note, however, that the
@@ -75,6 +75,14 @@ class ReferenceProcessor : public CHeapObj {
   // all collectors but the CMS collector).
   BoolObjectClosure* _is_alive_non_header;
 
+  // Soft ref clearing policies
+  // . the default policy
+  static ReferencePolicy*   _default_soft_ref_policy;
+  // . the "clear all" policy
+  static ReferencePolicy*   _always_clear_soft_ref_policy;
+  // . the current policy below is either one of the above
+  ReferencePolicy*          _current_soft_ref_policy;
+
   // The discovered ref lists themselves
 
   // The MT'ness degree of the queues below
@@ -90,6 +98,12 @@ class ReferenceProcessor : public CHeapObj {
   DiscoveredList* discovered_soft_refs() { return _discoveredSoftRefs; }
   static oop  sentinel_ref()             { return _sentinelRef; }
   static oop* adr_sentinel_ref()         { return &_sentinelRef; }
+  ReferencePolicy* snap_policy(bool always_clear) {
+    _current_soft_ref_policy = always_clear ?
+      _always_clear_soft_ref_policy : _default_soft_ref_policy;
+    _current_soft_ref_policy->snap();   // snapshot the policy threshold
+    return _current_soft_ref_policy;
+  }
 
  public:
   // Process references with a certain reachability level.
@@ -297,8 +311,7 @@ class ReferenceProcessor : public CHeapObj {
   bool discover_reference(oop obj, ReferenceType rt);
 
   // Process references found during GC (called by the garbage collector)
-  void process_discovered_references(ReferencePolicy*             policy,
-                                     BoolObjectClosure*           is_alive,
+  void process_discovered_references(BoolObjectClosure*           is_alive,
                                      OopClosure*                  keep_alive,
                                      VoidClosure*                 complete_gc,
                                      AbstractRefProcTaskExecutor* task_executor);

src/share/vm/memory/universe.cpp

@@ -96,7 +96,7 @@ bool            Universe::_bootstrapping = false;
 bool            Universe::_fully_initialized = false;
 
 size_t          Universe::_heap_capacity_at_last_gc;
-size_t          Universe::_heap_used_at_last_gc;
+size_t          Universe::_heap_used_at_last_gc = 0;
 
 CollectedHeap*  Universe::_collectedHeap = NULL;
 address         Universe::_heap_base = NULL;

src/share/vm/utilities/macros.hpp

@@ -65,8 +65,10 @@
 // COMPILER2 variant
 #ifdef COMPILER2
 #define COMPILER2_PRESENT(code) code
+#define NOT_COMPILER2(code)
 #else // COMPILER2
 #define COMPILER2_PRESENT(code)
+#define NOT_COMPILER2(code) code
 #endif // COMPILER2