/*

 * Copyright (c) 2000, 2009, 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

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 */

class SubTasksDone;

// A "GenCollectedHeap" is a SharedHeap that uses generational

// collection.  It is represented with a sequence of Generation's.

class GenCollectedHeap : public SharedHeap {

  friend class GenCollectorPolicy;

  friend class Generation;

  friend class DefNewGeneration;

  friend class TenuredGeneration;

  friend class ConcurrentMarkSweepGeneration;

  friend class CMSCollector;

  friend class GenMarkSweep;

  friend class VM_GenCollectForAllocation;

  friend class VM_GenCollectForPermanentAllocation;

  friend class VM_GenCollectFull;

  friend class VM_GenCollectFullConcurrent;

  friend class VM_GC_HeapInspection;

  friend class VM_HeapDumper;

  friend class HeapInspection;

  friend class GCCauseSetter;

  friend class VMStructs;

public:

  enum SomeConstants {

    max_gens = 10

  };

  friend class VM_PopulateDumpSharedSpace;

 protected:

  // Fields:

  static GenCollectedHeap* _gch;

 private:

  int _n_gens;

  Generation* _gens[max_gens];

  GenerationSpec** _gen_specs;

  // The generational collector policy.

  GenCollectorPolicy* _gen_policy;

  // If a generation would bail out of an incremental collection,

  // it sets this flag.  If the flag is set, satisfy_failed_allocation

  // will attempt allocating in all generations before doing a full GC.

  bool _incremental_collection_will_fail;

  bool _last_incremental_collection_failed;

  // In support of ExplicitGCInvokesConcurrent functionality

  unsigned int _full_collections_completed;

  // Data structure for claiming the (potentially) parallel tasks in

  // (gen-specific) strong roots processing.

  SubTasksDone* _gen_process_strong_tasks;

  // In block contents verification, the number of header words to skip

  NOT_PRODUCT(static size_t _skip_header_HeapWords;)

  // GC is not allowed during the dump of the shared classes.  Keep track

  // of this in order to provide an reasonable error message when terminating.

  bool _preloading_shared_classes;

protected:

  // Directs each generation up to and including "collectedGen" to recompute

  // its desired size.

  void compute_new_generation_sizes(int collectedGen);

  // Helper functions for allocation

  HeapWord* attempt_allocation(size_t size,

                               bool   is_tlab,

                               bool   first_only);

  // Helper function for two callbacks below.

  // Considers collection of the first max_level+1 generations.

  void do_collection(bool   full,

                     bool   clear_all_soft_refs,

                     size_t size,

                     bool   is_tlab,

                     int    max_level);

  // Callback from VM_GenCollectForAllocation operation.

  // This function does everything necessary/possible to satisfy an

  // allocation request that failed in the youngest generation that should

  // have handled it (including collection, expansion, etc.)

  HeapWord* satisfy_failed_allocation(size_t size, bool is_tlab);

  // Callback from VM_GenCollectFull operation.

  // Perform a full collection of the first max_level+1 generations.

  void do_full_collection(bool clear_all_soft_refs, int max_level);

  // Does the "cause" of GC indicate that

  // we absolutely __must__ clear soft refs?

  bool must_clear_all_soft_refs();

public:

  GenCollectedHeap(GenCollectorPolicy *policy);

  GCStats* gc_stats(int level) const;

  // Returns JNI_OK on success

  virtual jint initialize();

  char* allocate(size_t alignment, PermanentGenerationSpec* perm_gen_spec,

                 size_t* _total_reserved, int* _n_covered_regions,

                 ReservedSpace* heap_rs);

  // Does operations required after initialization has been done.

  void post_initialize();

  // Initialize ("weak") refs processing support

  virtual void ref_processing_init();

  virtual CollectedHeap::Name kind() const {

    return CollectedHeap::GenCollectedHeap;

  }

  // The generational collector policy.

  GenCollectorPolicy* gen_policy() const { return _gen_policy; }

  // Adaptive size policy

  virtual AdaptiveSizePolicy* size_policy() {

    return gen_policy()->size_policy();

  }

  size_t capacity() const;

  size_t used() const;

  // Save the "used_region" for generations level and lower,

  // and, if perm is true, for perm gen.

  void save_used_regions(int level, bool perm);

  size_t max_capacity() const;

  HeapWord* mem_allocate(size_t size,

                         bool   is_large_noref,

                         bool   is_tlab,

                         bool*  gc_overhead_limit_was_exceeded);

  // We may support a shared contiguous allocation area, if the youngest

  // generation does.

  bool supports_inline_contig_alloc() const;

  HeapWord** top_addr() const;

  HeapWord** end_addr() const;

  // Return an estimate of the maximum allocation that could be performed

  // without triggering any collection activity.  In a generational

  // collector, for example, this is probably the largest allocation that

  // could be supported in the youngest generation.  It is "unsafe" because

  // no locks are taken; the result should be treated as an approximation,

  // not a guarantee.

  size_t unsafe_max_alloc();

  // Does this heap support heap inspection? (+PrintClassHistogram)

  virtual bool supports_heap_inspection() const { return true; }

  // Perform a full collection of the heap; intended for use in implementing

  // "System.gc". This implies as full a collection as the CollectedHeap

  // supports. Caller does not hold the Heap_lock on entry.

  void collect(GCCause::Cause cause);

  // This interface assumes that it's being called by the

  // vm thread. It collects the heap assuming that the

  // heap lock is already held and that we are executing in

  // the context of the vm thread.

  void collect_as_vm_thread(GCCause::Cause cause);

  // The same as above but assume that the caller holds the Heap_lock.

  void collect_locked(GCCause::Cause cause);

  // Perform a full collection of the first max_level+1 generations.

  // Mostly used for testing purposes. Caller does not hold the Heap_lock on entry.

  void collect(GCCause::Cause cause, int max_level);

  // Returns "TRUE" iff "p" points into the allocated area of the heap.

  // The methods is_in(), is_in_closed_subset() and is_in_youngest() may

  // be expensive to compute in general, so, to prevent

  // their inadvertent use in product jvm's, we restrict their use to

  // assertion checking or verification only.

  bool is_in(const void* p) const;

  // override

  bool is_in_closed_subset(const void* p) const {

    if (UseConcMarkSweepGC) {

      return is_in_reserved(p);

    } else {

      return is_in(p);

    }

  }

  // Returns "TRUE" iff "p" points into the youngest generation.

  bool is_in_youngest(void* p);

  // Iteration functions.

  void oop_iterate(OopClosure* cl);

  void oop_iterate(MemRegion mr, OopClosure* cl);

  void object_iterate(ObjectClosure* cl);

  void safe_object_iterate(ObjectClosure* cl);

  void object_iterate_since_last_GC(ObjectClosure* cl);

  Space* space_containing(const void* addr) const;

  // A CollectedHeap is divided into a dense sequence of "blocks"; that is,

  // each address in the (reserved) heap is a member of exactly

  // one block.  The defining characteristic of a block is that it is

  // possible to find its size, and thus to progress forward to the next

  // block.  (Blocks may be of different sizes.)  Thus, blocks may

  // represent Java objects, or they might be free blocks in a

  // free-list-based heap (or subheap), as long as the two kinds are

  // distinguishable and the size of each is determinable.

  // Returns the address of the start of the "block" that contains the

  // address "addr".  We say "blocks" instead of "object" since some heaps

  // may not pack objects densely; a chunk may either be an object or a

  // non-object.

  virtual HeapWord* block_start(const void* addr) const;

  // Requires "addr" to be the start of a chunk, and returns its size.

  // "addr + size" is required to be the start of a new chunk, or the end

  // of the active area of the heap. Assumes (and verifies in non-product

  // builds) that addr is in the allocated part of the heap and is

  // the start of a chunk.

  virtual size_t block_size(const HeapWord* addr) const;

  // Requires "addr" to be the start of a block, and returns "TRUE" iff

  // the block is an object. Assumes (and verifies in non-product

  // builds) that addr is in the allocated part of the heap and is

  // the start of a chunk.

  virtual bool block_is_obj(const HeapWord* addr) const;

  // Section on TLAB's.

  virtual bool supports_tlab_allocation() const;

  virtual size_t tlab_capacity(Thread* thr) const;

  virtual size_t unsafe_max_tlab_alloc(Thread* thr) const;

  virtual HeapWord* allocate_new_tlab(size_t size);

  // Can a compiler initialize a new object without store barriers?

  // This permission only extends from the creation of a new object

  // via a TLAB up to the first subsequent safepoint.

  virtual bool can_elide_tlab_store_barriers() const {

    return true;

  }

  virtual bool card_mark_must_follow_store() const {

    return UseConcMarkSweepGC;

  }

  // We don't need barriers for stores to objects in the

  // young gen and, a fortiori, for initializing stores to

  // objects therein. This applies to {DefNew,ParNew}+{Tenured,CMS}

  // only and may need to be re-examined in case other

  // kinds of collectors are implemented in the future.

  virtual bool can_elide_initializing_store_barrier(oop new_obj) {

    // We wanted to assert that:-

    // assert(UseParNewGC || UseSerialGC || UseConcMarkSweepGC,

    //       "Check can_elide_initializing_store_barrier() for this collector");

    // but unfortunately the flag UseSerialGC need not necessarily always

    // be set when DefNew+Tenured are being used.

    return is_in_youngest((void*)new_obj);

  }

  // Can a compiler elide a store barrier when it writes

  // a permanent oop into the heap?  Applies when the compiler

  // is storing x to the heap, where x->is_perm() is true.

  virtual bool can_elide_permanent_oop_store_barriers() const {

    // CMS needs to see all, even intra-generational, ref updates.

    return !UseConcMarkSweepGC;

  }

  // The "requestor" generation is performing some garbage collection

  // action for which it would be useful to have scratch space.  The

  // requestor promises to allocate no more than "max_alloc_words" in any

  // older generation (via promotion say.)   Any blocks of space that can

  // be provided are returned as a list of ScratchBlocks, sorted by

  // decreasing size.

  ScratchBlock* gather_scratch(Generation* requestor, size_t max_alloc_words);

  // Allow each generation to reset any scratch space that it has

  // contributed as it needs.

  void release_scratch();

  size_t large_typearray_limit();

  // Ensure parsability: override

  virtual void ensure_parsability(bool retire_tlabs);

  // Time in ms since the longest time a collector ran in

  // in any generation.

  virtual jlong millis_since_last_gc();

  // Total number of full collections completed.

  unsigned int total_full_collections_completed() {

    assert(_full_collections_completed <= _total_full_collections,

           "Can't complete more collections than were started");

    return _full_collections_completed;

  }

  // Update above counter, as appropriate, at the end of a stop-world GC cycle

  unsigned int update_full_collections_completed();

  // Update above counter, as appropriate, at the end of a concurrent GC cycle

  unsigned int update_full_collections_completed(unsigned int count);

  // Update "time of last gc" for all constituent generations

  // to "now".

  void update_time_of_last_gc(jlong now) {

    for (int i = 0; i < _n_gens; i++) {

      _gens[i]->update_time_of_last_gc(now);

    }

    perm_gen()->update_time_of_last_gc(now);

  }

  // Update the gc statistics for each generation.

  // "level" is the level of the lastest collection

  void update_gc_stats(int current_level, bool full) {

    for (int i = 0; i < _n_gens; i++) {

      _gens[i]->update_gc_stats(current_level, full);

    }

    perm_gen()->update_gc_stats(current_level, full);

  }

  // Override.

  bool no_gc_in_progress() { return !is_gc_active(); }

  // Override.

  void prepare_for_verify();

  // Override.

  void verify(bool allow_dirty, bool silent, bool /* option */);

  // Override.

  void print() const;

  void print_on(outputStream* st) const;

  virtual void print_gc_threads_on(outputStream* st) const;

  virtual void gc_threads_do(ThreadClosure* tc) const;

  virtual void print_tracing_info() const;

  // PrintGC, PrintGCDetails support

  void print_heap_change(size_t prev_used) const;

  void print_perm_heap_change(size_t perm_prev_used) const;

  // The functions below are helper functions that a subclass of

  // "CollectedHeap" can use in the implementation of its virtual

  // functions.

  class GenClosure : public StackObj {

   public:

    virtual void do_generation(Generation* gen) = 0;

  };

  // Apply "cl.do_generation" to all generations in the heap (not including

  // the permanent generation).  If "old_to_young" determines the order.

  void generation_iterate(GenClosure* cl, bool old_to_young);

  void space_iterate(SpaceClosure* cl);

  // Return "true" if all generations (but perm) have reached the

  // maximal committed limit that they can reach, without a garbage

  // collection.

  virtual bool is_maximal_no_gc() const;

  // Return the generation before "gen", or else NULL.

  Generation* prev_gen(Generation* gen) const {

    int l = gen->level();

    if (l == 0) return NULL;

    else return _gens[l-1];

  }

  // Return the generation after "gen", or else NULL.

  Generation* next_gen(Generation* gen) const {

    int l = gen->level() + 1;

    if (l == _n_gens) return NULL;

    else return _gens[l];

  }

  Generation* get_gen(int i) const {

    if (i >= 0 && i < _n_gens)

      return _gens[i];

    else

      return NULL;

  }

  int n_gens() const {

    assert(_n_gens == gen_policy()->number_of_generations(), "Sanity");

    return _n_gens;

  }

  // Convenience function to be used in situations where the heap type can be

  // asserted to be this type.

  static GenCollectedHeap* heap();

  void set_par_threads(int t);

  // Invoke the "do_oop" method of one of the closures "not_older_gens"

  // or "older_gens" on root locations for the generation at

  // "level".  (The "older_gens" closure is used for scanning references

  // from older generations; "not_older_gens" is used everywhere else.)

  // If "younger_gens_as_roots" is false, younger generations are

  // not scanned as roots; in this case, the caller must be arranging to

  // scan the younger generations itself.  (For example, a generation might

  // explicitly mark reachable objects in younger generations, to avoid

  // excess storage retention.)  If "collecting_perm_gen" is false, then

  // roots that may only contain references to permGen objects are not

  // scanned. The "so" argument determines which of the roots

  // the closure is applied to:

  // "SO_None" does none;

  // "SO_AllClasses" applies the closure to all entries in the SystemDictionary;

  // "SO_SystemClasses" to all the "system" classes and loaders;

  // "SO_Symbols_and_Strings" applies the closure to all entries in

  // SymbolsTable and StringTable.

  void gen_process_strong_roots(int level,

                                bool younger_gens_as_roots,

                                // The remaining arguments are in an order

                                // consistent with SharedHeap::process_strong_roots:

                                bool activate_scope,

                                bool collecting_perm_gen,

                                SharedHeap::ScanningOption so,

                                OopsInGenClosure* not_older_gens,

                                bool do_code_roots,

                                OopsInGenClosure* older_gens);

  // Apply "blk" to all the weak roots of the system.  These include

  // JNI weak roots, the code cache, system dictionary, symbol table,

  // string table, and referents of reachable weak refs.

  void gen_process_weak_roots(OopClosure* root_closure,

                              CodeBlobClosure* code_roots,

                              OopClosure* non_root_closure);

  // Set the saved marks of generations, if that makes sense.

  // In particular, if any generation might iterate over the oops

  // in other generations, it should call this method.

  void save_marks();

  // Apply "cur->do_oop" or "older->do_oop" to all the oops in objects

  // allocated since the last call to save_marks in generations at or above

  // "level" (including the permanent generation.)  The "cur" closure is

  // applied to references in the generation at "level", and the "older"

  // closure to older (and permanent) generations.

#define GCH_SINCE_SAVE_MARKS_ITERATE_DECL(OopClosureType, nv_suffix)    \

  void oop_since_save_marks_iterate(int level,                          \

                                    OopClosureType* cur,                \

                                    OopClosureType* older);

  ALL_SINCE_SAVE_MARKS_CLOSURES(GCH_SINCE_SAVE_MARKS_ITERATE_DECL)

#undef GCH_SINCE_SAVE_MARKS_ITERATE_DECL

  // Returns "true" iff no allocations have occurred in any generation at

  // "level" or above (including the permanent generation) since the last

  // call to "save_marks".

  bool no_allocs_since_save_marks(int level);

  // If a generation bails out of an incremental collection,

  // it sets this flag.

  bool incremental_collection_will_fail() {

    return _incremental_collection_will_fail;

  }

  void set_incremental_collection_will_fail() {

    _incremental_collection_will_fail = true;

  }

  void clear_incremental_collection_will_fail() {

    _incremental_collection_will_fail = false;

  }

  bool last_incremental_collection_failed() const {

    return _last_incremental_collection_failed;

  }

  void set_last_incremental_collection_failed() {

    _last_incremental_collection_failed = true;

  }

  void clear_last_incremental_collection_failed() {

    _last_incremental_collection_failed = false;

  }

  // Promotion of obj into gen failed.  Try to promote obj to higher non-perm

  // gens in ascending order; return the new location of obj if successful.

  // Otherwise, try expand-and-allocate for obj in each generation starting at

  // gen; return the new location of obj if successful.  Otherwise, return NULL.

  oop handle_failed_promotion(Generation* gen,

                              oop obj,

                              size_t obj_size);

private:

  // Accessor for memory state verification support

  NOT_PRODUCT(

    static size_t skip_header_HeapWords() { return _skip_header_HeapWords; }

  )

  // Override

  void check_for_non_bad_heap_word_value(HeapWord* addr,

    size_t size) PRODUCT_RETURN;

  // For use by mark-sweep.  As implemented, mark-sweep-compact is global

  // in an essential way: compaction is performed across generations, by

  // iterating over spaces.

  void prepare_for_compaction();

  // Perform a full collection of the first max_level+1 generations.

  // This is the low level interface used by the public versions of

  // collect() and collect_locked(). Caller holds the Heap_lock on entry.

  void collect_locked(GCCause::Cause cause, int max_level);

  // Returns success or failure.

  bool create_cms_collector();