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src/hotspot/share/gc/shenandoah/shenandoahHeap.hpp

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@@ -1,8 +1,9 @@
  /*
   * Copyright (c) 2023, 2024, Oracle and/or its affiliates. All rights reserved.
   * Copyright (c) 2013, 2021, Red Hat, Inc. All rights reserved.
+  * Copyright Amazon.com Inc. 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.

@@ -28,14 +29,20 @@
  
  #include "gc/shared/markBitMap.hpp"
  #include "gc/shared/softRefPolicy.hpp"
  #include "gc/shared/collectedHeap.hpp"
  #include "gc/shenandoah/heuristics/shenandoahSpaceInfo.hpp"
- #include "gc/shenandoah/shenandoahAsserts.hpp"
  #include "gc/shenandoah/shenandoahAllocRequest.hpp"
+ #include "gc/shenandoah/shenandoahAsserts.hpp"
+ #include "gc/shenandoah/shenandoahController.hpp"
  #include "gc/shenandoah/shenandoahLock.hpp"
  #include "gc/shenandoah/shenandoahEvacOOMHandler.hpp"
+ #include "gc/shenandoah/shenandoahEvacTracker.hpp"
+ #include "gc/shenandoah/shenandoahGenerationType.hpp"
+ #include "gc/shenandoah/shenandoahGenerationSizer.hpp"
+ #include "gc/shenandoah/shenandoahMmuTracker.hpp"
+ #include "gc/shenandoah/mode/shenandoahMode.hpp"
  #include "gc/shenandoah/shenandoahPadding.hpp"
  #include "gc/shenandoah/shenandoahSharedVariables.hpp"
  #include "gc/shenandoah/shenandoahUnload.hpp"
  #include "memory/metaspace.hpp"
  #include "services/memoryManager.hpp"

@@ -43,13 +50,15 @@
  #include "utilities/stack.hpp"
  
  class ConcurrentGCTimer;
  class ObjectIterateScanRootClosure;
  class ShenandoahCollectorPolicy;
- class ShenandoahControlThread;
  class ShenandoahGCSession;
  class ShenandoahGCStateResetter;
+ class ShenandoahGeneration;
+ class ShenandoahYoungGeneration;
+ class ShenandoahOldGeneration;
  class ShenandoahHeuristics;
  class ShenandoahMarkingContext;
  class ShenandoahMode;
  class ShenandoahPhaseTimings;
  class ShenandoahHeap;

@@ -111,38 +120,85 @@
  
  typedef ShenandoahLock    ShenandoahHeapLock;
  typedef ShenandoahLocker  ShenandoahHeapLocker;
  typedef Stack<oop, mtGC>  ShenandoahScanObjectStack;
  
+ class ShenandoahSynchronizePinnedRegionStates : public ShenandoahHeapRegionClosure {
+ private:
+   ShenandoahHeapLock* const _lock;
+ 
+ public:
+   ShenandoahSynchronizePinnedRegionStates();
+ 
+   void heap_region_do(ShenandoahHeapRegion* r) override;
+   bool is_thread_safe() override { return true; }
+ };
+ 
  // Shenandoah GC is low-pause concurrent GC that uses Brooks forwarding pointers
  // to encode forwarding data. See BrooksPointer for details on forwarding data encoding.
  // See ShenandoahControlThread for GC cycle structure.
  //
- class ShenandoahHeap : public CollectedHeap, public ShenandoahSpaceInfo {
+ class ShenandoahHeap : public CollectedHeap {
    friend class ShenandoahAsserts;
    friend class VMStructs;
    friend class ShenandoahGCSession;
    friend class ShenandoahGCStateResetter;
    friend class ShenandoahParallelObjectIterator;
    friend class ShenandoahSafepoint;
  
    // Supported GC
    friend class ShenandoahConcurrentGC;
+   friend class ShenandoahOldGC;
    friend class ShenandoahDegenGC;
    friend class ShenandoahFullGC;
    friend class ShenandoahUnload;
  
  // ---------- Locks that guard important data structures in Heap
  //
  private:
    ShenandoahHeapLock _lock;
  
+   // Indicates the generation whose collection is in
+   // progress. Mutator threads aren't allowed to read
+   // this field.
+   ShenandoahGeneration* _gc_generation;
+ 
+   // This is set and cleared by only the VMThread
+   // at each STW pause (safepoint) to the value seen in
+   // _gc_generation. This allows the value to be always consistently
+   // seen by all mutators as well as all GC worker threads.
+   // In that sense, it's a stable snapshot of _gc_generation that is
+   // updated at each STW pause associated with a ShenandoahVMOp.
+   ShenandoahGeneration* _active_generation;
+ 
  public:
    ShenandoahHeapLock* lock() {
      return &_lock;
    }
  
+   ShenandoahGeneration* gc_generation() const {
+     // We don't want this field read by a mutator thread
+     assert(!Thread::current()->is_Java_thread(), "Not allowed");
+     // value of _gc_generation field, see above
+     return _gc_generation;
+   }
+ 
+   ShenandoahGeneration* active_generation() const {
+     // value of _active_generation field, see above
+     return _active_generation;
+   }
+ 
+   // Set the _gc_generation field
+   void set_gc_generation(ShenandoahGeneration* generation);
+ 
+   // Copy the value in the _gc_generation field into
+   // the _active_generation field: can only be called at
+   // a safepoint by the VMThread.
+   void set_active_generation();
+ 
+   ShenandoahHeuristics* heuristics();
+ 
  // ---------- Initialization, termination, identification, printing routines
  //
  public:
    static ShenandoahHeap* heap();
  

@@ -151,12 +207,12 @@
  
    ShenandoahHeap(ShenandoahCollectorPolicy* policy);
    jint initialize() override;
    void post_initialize() override;
    void initialize_mode();
-   void initialize_heuristics();
- 
+   virtual void initialize_heuristics();
+   virtual void print_init_logger() const;
    void initialize_serviceability() override;
  
    void print_on(outputStream* st)              const override;
    void print_extended_on(outputStream *st)     const override;
    void print_tracing_info()                    const override;

@@ -173,39 +229,38 @@
    }
  
  // ---------- Heap counters and metrics
  //
  private:
-            size_t _initial_size;
-            size_t _minimum_size;
+   size_t _initial_size;
+   size_t _minimum_size;
+ 
    volatile size_t _soft_max_size;
    shenandoah_padding(0);
-   volatile size_t _used;
    volatile size_t _committed;
-   volatile size_t _bytes_allocated_since_gc_start;
    shenandoah_padding(1);
  
+   void increase_used(const ShenandoahAllocRequest& req);
+ 
  public:
-   void increase_used(size_t bytes);
-   void decrease_used(size_t bytes);
-   void set_used(size_t bytes);
+   void increase_used(ShenandoahGeneration* generation, size_t bytes);
+   void decrease_used(ShenandoahGeneration* generation, size_t bytes);
+   void increase_humongous_waste(ShenandoahGeneration* generation, size_t bytes);
+   void decrease_humongous_waste(ShenandoahGeneration* generation, size_t bytes);
  
    void increase_committed(size_t bytes);
    void decrease_committed(size_t bytes);
-   void increase_allocated(size_t bytes);
  
-   size_t bytes_allocated_since_gc_start() const override;
    void reset_bytes_allocated_since_gc_start();
  
    size_t min_capacity()      const;
    size_t max_capacity()      const override;
-   size_t soft_max_capacity() const override;
+   size_t soft_max_capacity() const;
    size_t initial_capacity()  const;
    size_t capacity()          const override;
    size_t used()              const override;
    size_t committed()         const;
-   size_t available()         const override;
  
    void set_soft_max_capacity(size_t v);
  
  // ---------- Periodic Tasks
  //

@@ -221,10 +276,12 @@
  private:
    uint _max_workers;
    ShenandoahWorkerThreads* _workers;
    ShenandoahWorkerThreads* _safepoint_workers;
  
+   virtual void initialize_controller();
+ 
  public:
    uint max_workers();
    void assert_gc_workers(uint nworker) NOT_DEBUG_RETURN;
  
    WorkerThreads* workers() const;

@@ -237,11 +294,11 @@
  private:
    MemRegion _heap_region;
    bool      _heap_region_special;
    size_t    _num_regions;
    ShenandoahHeapRegion** _regions;
-   ShenandoahRegionIterator _update_refs_iterator;
+   uint8_t* _affiliations;       // Holds array of enum ShenandoahAffiliation, including FREE status in non-generational mode
  
  public:
  
    inline HeapWord* base() const { return _heap_region.start(); }
  

@@ -254,10 +311,12 @@
    inline ShenandoahHeapRegion* get_region(size_t region_idx) const;
  
    void heap_region_iterate(ShenandoahHeapRegionClosure* blk) const;
    void parallel_heap_region_iterate(ShenandoahHeapRegionClosure* blk) const;
  
+   inline ShenandoahMmuTracker* mmu_tracker() { return &_mmu_tracker; };
+ 
  // ---------- GC state machinery
  //
  // GC state describes the important parts of collector state, that may be
  // used to make barrier selection decisions in the native and generated code.
  // Multiple bits can be set at once.

@@ -269,36 +328,43 @@
    enum GCStateBitPos {
      // Heap has forwarded objects: needs LRB barriers.
      HAS_FORWARDED_BITPOS   = 0,
  
      // Heap is under marking: needs SATB barriers.
+     // For generational mode, it means either young or old marking, or both.
      MARKING_BITPOS    = 1,
  
      // Heap is under evacuation: needs LRB barriers. (Set together with HAS_FORWARDED)
      EVACUATION_BITPOS = 2,
  
      // Heap is under updating: needs no additional barriers.
      UPDATEREFS_BITPOS = 3,
  
      // Heap is under weak-reference/roots processing: needs weak-LRB barriers.
      WEAK_ROOTS_BITPOS  = 4,
+ 
+     // Young regions are under marking, need SATB barriers.
+     YOUNG_MARKING_BITPOS = 5,
+ 
+     // Old regions are under marking, need SATB barriers.
+     OLD_MARKING_BITPOS = 6
    };
  
    enum GCState {
      STABLE        = 0,
      HAS_FORWARDED = 1 << HAS_FORWARDED_BITPOS,
      MARKING       = 1 << MARKING_BITPOS,
      EVACUATION    = 1 << EVACUATION_BITPOS,
      UPDATEREFS    = 1 << UPDATEREFS_BITPOS,
      WEAK_ROOTS    = 1 << WEAK_ROOTS_BITPOS,
+     YOUNG_MARKING = 1 << YOUNG_MARKING_BITPOS,
+     OLD_MARKING   = 1 << OLD_MARKING_BITPOS
    };
  
  private:
    bool _gc_state_changed;
    ShenandoahSharedBitmap _gc_state;
- 
-   // tracks if new regions have been allocated or retired since last check
    ShenandoahSharedFlag   _heap_changed;
    ShenandoahSharedFlag   _degenerated_gc_in_progress;
    ShenandoahSharedFlag   _full_gc_in_progress;
    ShenandoahSharedFlag   _full_gc_move_in_progress;
    ShenandoahSharedFlag   _concurrent_strong_root_in_progress;

@@ -323,11 +389,12 @@
    // uncommitted since the previous calls. This call will reset the flag to false.
    bool has_changed() {
      return _heap_changed.try_unset();
    }
  
-   void set_concurrent_mark_in_progress(bool in_progress);
+   void set_concurrent_young_mark_in_progress(bool in_progress);
+   void set_concurrent_old_mark_in_progress(bool in_progress);
    void set_evacuation_in_progress(bool in_progress);
    void set_update_refs_in_progress(bool in_progress);
    void set_degenerated_gc_in_progress(bool in_progress);
    void set_full_gc_in_progress(bool in_progress);
    void set_full_gc_move_in_progress(bool in_progress);

@@ -335,43 +402,55 @@
    void set_concurrent_strong_root_in_progress(bool cond);
    void set_concurrent_weak_root_in_progress(bool cond);
  
    inline bool is_stable() const;
    inline bool is_idle() const;
+ 
    inline bool is_concurrent_mark_in_progress() const;
+   inline bool is_concurrent_young_mark_in_progress() const;
+   inline bool is_concurrent_old_mark_in_progress() const;
    inline bool is_update_refs_in_progress() const;
    inline bool is_evacuation_in_progress() const;
    inline bool is_degenerated_gc_in_progress() const;
    inline bool is_full_gc_in_progress() const;
    inline bool is_full_gc_move_in_progress() const;
    inline bool has_forwarded_objects() const;
  
    inline bool is_stw_gc_in_progress() const;
    inline bool is_concurrent_strong_root_in_progress() const;
    inline bool is_concurrent_weak_root_in_progress() const;
+   bool is_prepare_for_old_mark_in_progress() const;
  
  private:
+   void manage_satb_barrier(bool active);
+ 
    enum CancelState {
      // Normal state. GC has not been cancelled and is open for cancellation.
      // Worker threads can suspend for safepoint.
      CANCELLABLE,
  
      // GC has been cancelled. Worker threads can not suspend for
      // safepoint but must finish their work as soon as possible.
      CANCELLED
    };
  
+   double _cancel_requested_time;
    ShenandoahSharedEnumFlag<CancelState> _cancelled_gc;
+ 
+   // Returns true if cancel request was successfully communicated.
+   // Returns false if some other thread already communicated cancel
+   // request.  A true return value does not mean GC has been
+   // cancelled, only that the process of cancelling GC has begun.
    bool try_cancel_gc();
  
  public:
- 
    inline bool cancelled_gc() const;
    inline bool check_cancelled_gc_and_yield(bool sts_active = true);
  
-   inline void clear_cancelled_gc();
+   inline void clear_cancelled_gc(bool clear_oom_handler = true);
  
+   void cancel_concurrent_mark();
    void cancel_gc(GCCause::Cause cause);
  
  public:
    // These will uncommit empty regions if heap::committed > shrink_until
    // and there exists at least one region which was made empty before shrink_before.

@@ -379,59 +458,88 @@
    void op_uncommit(double shrink_before, size_t shrink_until);
  
    // Returns true if the soft maximum heap has been changed using management APIs.
    bool check_soft_max_changed();
  
+ protected:
+   // This is shared between shConcurrentGC and shDegenerateGC so that degenerated
+   // GC can resume update refs from where the concurrent GC was cancelled. It is
+   // also used in shGenerationalHeap, which uses a different closure for update refs.
+   ShenandoahRegionIterator _update_refs_iterator;
+ 
  private:
    // GC support
-   // Reset bitmap, prepare regions for new GC cycle
-   void prepare_gc();
-   void prepare_regions_and_collection_set(bool concurrent);
    // Evacuation
-   void evacuate_collection_set(bool concurrent);
+   virtual void evacuate_collection_set(bool concurrent);
    // Concurrent root processing
    void prepare_concurrent_roots();
    void finish_concurrent_roots();
    // Concurrent class unloading support
    void do_class_unloading();
    // Reference updating
    void prepare_update_heap_references(bool concurrent);
-   void update_heap_references(bool concurrent);
+   virtual void update_heap_references(bool concurrent);
    // Final update region states
    void update_heap_region_states(bool concurrent);
-   void rebuild_free_set(bool concurrent);
+   virtual void final_update_refs_update_region_states();
  
    void rendezvous_threads(const char* name);
    void recycle_trash();
  public:
+   void rebuild_free_set(bool concurrent);
    void notify_gc_progress();
    void notify_gc_no_progress();
    size_t get_gc_no_progress_count() const;
  
  //
  // Mark support
  private:
-   ShenandoahControlThread*   _control_thread;
+   ShenandoahGeneration*  _global_generation;
+ 
+ protected:
+   ShenandoahController*  _control_thread;
+ 
+   ShenandoahYoungGeneration* _young_generation;
+   ShenandoahOldGeneration*   _old_generation;
+ 
+ private:
    ShenandoahCollectorPolicy* _shenandoah_policy;
    ShenandoahMode*            _gc_mode;
-   ShenandoahHeuristics*      _heuristics;
    ShenandoahFreeSet*         _free_set;
    ShenandoahPacer*           _pacer;
    ShenandoahVerifier*        _verifier;
  
-   ShenandoahPhaseTimings*    _phase_timings;
- 
-   ShenandoahControlThread*   control_thread()          { return _control_thread;    }
+   ShenandoahPhaseTimings*       _phase_timings;
+   ShenandoahMmuTracker          _mmu_tracker;
  
  public:
+   ShenandoahController*   control_thread() { return _control_thread; }
+ 
+   ShenandoahGeneration*      global_generation() const { return _global_generation; }
+   ShenandoahYoungGeneration* young_generation()  const {
+     assert(mode()->is_generational(), "Young generation requires generational mode");
+     return _young_generation;
+   }
+ 
+   ShenandoahOldGeneration*   old_generation()    const {
+     assert(mode()->is_generational(), "Old generation requires generational mode");
+     return _old_generation;
+   }
+ 
+   ShenandoahGeneration*      generation_for(ShenandoahAffiliation affiliation) const;
+ 
    ShenandoahCollectorPolicy* shenandoah_policy() const { return _shenandoah_policy; }
    ShenandoahMode*            mode()              const { return _gc_mode;           }
-   ShenandoahHeuristics*      heuristics()        const { return _heuristics;        }
    ShenandoahFreeSet*         free_set()          const { return _free_set;          }
    ShenandoahPacer*           pacer()             const { return _pacer;             }
  
-   ShenandoahPhaseTimings*    phase_timings()     const { return _phase_timings;     }
+   ShenandoahPhaseTimings*      phase_timings()   const { return _phase_timings;     }
+ 
+   ShenandoahEvacOOMHandler* oom_evac_handler() { return &_oom_evac_handler; }
+ 
+   void on_cycle_start(GCCause::Cause cause, ShenandoahGeneration* generation);
+   void on_cycle_end(ShenandoahGeneration* generation);
  
    ShenandoahVerifier*        verifier();
  
  // ---------- VM subsystem bindings
  //

@@ -442,28 +550,20 @@
    GCMemoryManager              _cycle_memory_manager;
    ConcurrentGCTimer*           _gc_timer;
    // For exporting to SA
    int                          _log_min_obj_alignment_in_bytes;
  public:
-   ShenandoahMonitoringSupport* monitoring_support()          { return _monitoring_support;    }
+   ShenandoahMonitoringSupport* monitoring_support() const    { return _monitoring_support;    }
    GCMemoryManager* cycle_memory_manager()                    { return &_cycle_memory_manager; }
    GCMemoryManager* stw_memory_manager()                      { return &_stw_memory_manager;   }
  
    GrowableArray<GCMemoryManager*> memory_managers() override;
    GrowableArray<MemoryPool*> memory_pools() override;
    MemoryUsage memory_usage() override;
    GCTracer* tracer();
    ConcurrentGCTimer* gc_timer() const;
  
- // ---------- Reference processing
- //
- private:
-   ShenandoahReferenceProcessor* const _ref_processor;
- 
- public:
-   ShenandoahReferenceProcessor* ref_processor() { return _ref_processor; }
- 
  // ---------- Class Unloading
  //
  private:
    ShenandoahSharedFlag _unload_classes;
    ShenandoahUnload     _unloader;

@@ -478,10 +578,13 @@
  private:
    void stw_unload_classes(bool full_gc);
    void stw_process_weak_roots(bool full_gc);
    void stw_weak_refs(bool full_gc);
  
+   inline void assert_lock_for_affiliation(ShenandoahAffiliation orig_affiliation,
+                                           ShenandoahAffiliation new_affiliation);
+ 
    // Heap iteration support
    void scan_roots_for_iteration(ShenandoahScanObjectStack* oop_stack, ObjectIterateScanRootClosure* oops);
    bool prepare_aux_bitmap_for_iteration();
    void reclaim_aux_bitmap_for_iteration();
  

@@ -495,10 +598,20 @@
  
    // Check the pointer is in active part of Java heap.
    // Use is_in_reserved to check if object is within heap bounds.
    bool is_in(const void* p) const override;
  
+   inline bool is_in_active_generation(oop obj) const;
+   inline bool is_in_young(const void* p) const;
+   inline bool is_in_old(const void* p) const;
+   inline bool is_old(oop pobj) const;
+ 
+   inline ShenandoahAffiliation region_affiliation(const ShenandoahHeapRegion* r);
+   inline void set_affiliation(ShenandoahHeapRegion* r, ShenandoahAffiliation new_affiliation);
+ 
+   inline ShenandoahAffiliation region_affiliation(size_t index);
+ 
    bool requires_barriers(stackChunkOop obj) const override;
  
    MemRegion reserved_region() const { return _reserved; }
    bool is_in_reserved(const void* addr) const { return _reserved.contains(addr); }
  

@@ -541,30 +654,32 @@
    void sync_pinned_region_status();
    void assert_pinned_region_status() NOT_DEBUG_RETURN;
  
  // ---------- CDS archive support
  
-   bool can_load_archived_objects() const override { return UseCompressedOops; }
+   bool can_load_archived_objects() const override { return UseCompressedOops && !ShenandoahCardBarrier; }
    HeapWord* allocate_loaded_archive_space(size_t size) override;
    void complete_loaded_archive_space(MemRegion archive_space) override;
  
  // ---------- Allocation support
  //
+ protected:
+   inline HeapWord* allocate_from_gclab(Thread* thread, size_t size);
+ 
  private:
    HeapWord* allocate_memory_under_lock(ShenandoahAllocRequest& request, bool& in_new_region);
-   inline HeapWord* allocate_from_gclab(Thread* thread, size_t size);
    HeapWord* allocate_from_gclab_slow(Thread* thread, size_t size);
    HeapWord* allocate_new_gclab(size_t min_size, size_t word_size, size_t* actual_size);
  
  public:
    HeapWord* allocate_memory(ShenandoahAllocRequest& request);
    HeapWord* mem_allocate(size_t size, bool* what) override;
    MetaWord* satisfy_failed_metadata_allocation(ClassLoaderData* loader_data,
                                                 size_t size,
                                                 Metaspace::MetadataType mdtype) override;
  
-   void notify_mutator_alloc_words(size_t words, bool waste);
+   void notify_mutator_alloc_words(size_t words, size_t waste);
  
    HeapWord* allocate_new_tlab(size_t min_size, size_t requested_size, size_t* actual_size) override;
    size_t tlab_capacity(Thread *thr) const override;
    size_t unsafe_max_tlab_alloc(Thread *thread) const override;
    size_t max_tlab_size() const override;

@@ -598,24 +713,20 @@
    ShenandoahLiveData** _liveness_cache;
  
  public:
    inline ShenandoahMarkingContext* complete_marking_context() const;
    inline ShenandoahMarkingContext* marking_context() const;
-   inline void mark_complete_marking_context();
-   inline void mark_incomplete_marking_context();
  
    template<class T>
    inline void marked_object_iterate(ShenandoahHeapRegion* region, T* cl);
  
    template<class T>
    inline void marked_object_iterate(ShenandoahHeapRegion* region, T* cl, HeapWord* limit);
  
    template<class T>
    inline void marked_object_oop_iterate(ShenandoahHeapRegion* region, T* cl, HeapWord* limit);
  
-   void reset_mark_bitmap();
- 
    // SATB barriers hooks
    inline bool requires_marking(const void* entry) const;
  
    // Support for bitmap uncommits
    bool commit_bitmap_slice(ShenandoahHeapRegion *r);

@@ -632,24 +743,26 @@
  //
  private:
    ShenandoahCollectionSet* _collection_set;
    ShenandoahEvacOOMHandler _oom_evac_handler;
  
+   oop try_evacuate_object(oop src, Thread* thread, ShenandoahHeapRegion* from_region, ShenandoahAffiliation target_gen);
  public:
+ 
    static address in_cset_fast_test_addr();
  
    ShenandoahCollectionSet* collection_set() const { return _collection_set; }
  
    // Checks if object is in the collection set.
    inline bool in_collection_set(oop obj) const;
  
    // Checks if location is in the collection set. Can be interior pointer, not the oop itself.
    inline bool in_collection_set_loc(void* loc) const;
  
-   // Evacuates object src. Returns the evacuated object, either evacuated
+   // Evacuates or promotes object src. Returns the evacuated object, either evacuated
    // by this thread, or by some other thread.
-   oop evacuate_object(oop src, Thread* thread);
+   virtual oop evacuate_object(oop src, Thread* thread);
  
    // Call before/after evacuation.
    inline void enter_evacuation(Thread* t);
    inline void leave_evacuation(Thread* t);
  

@@ -672,11 +785,20 @@
  
    static inline void atomic_clear_oop(      oop* addr,       oop compare);
    static inline void atomic_clear_oop(narrowOop* addr,       oop compare);
    static inline void atomic_clear_oop(narrowOop* addr, narrowOop compare);
  
-   void trash_humongous_region_at(ShenandoahHeapRegion *r);
+   size_t trash_humongous_region_at(ShenandoahHeapRegion *r);
+ 
+   static inline void increase_object_age(oop obj, uint additional_age);
+ 
+   // Return the object's age, or a sentinel value when the age can't
+   // necessarily be determined because of concurrent locking by the
+   // mutator
+   static inline uint get_object_age(oop obj);
+ 
+   void log_heap_status(const char *msg) const;
  
  private:
    void trash_cset_regions();
  
  // ---------- Testing helpers functions
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