/*

 * Copyright (c) 1997, 2017, 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.

 *

 */

#ifndef SHARE_VM_GC_SHARED_GENERATION_HPP

#define SHARE_VM_GC_SHARED_GENERATION_HPP

#include "gc/shared/collectorCounters.hpp"

#include "gc/shared/referenceProcessor.hpp"

#include "logging/log.hpp"

#include "memory/allocation.hpp"

#include "memory/memRegion.hpp"

#include "memory/universe.hpp"

#include "memory/virtualspace.hpp"

#include "runtime/mutex.hpp"

#include "runtime/perfData.hpp"

// A Generation models a heap area for similarly-aged objects.

// It will contain one ore more spaces holding the actual objects.

//

// The Generation class hierarchy:

//

// Generation                      - abstract base class

// - DefNewGeneration              - allocation area (copy collected)

//   - ParNewGeneration            - a DefNewGeneration that is collected by

//                                   several threads

// - CardGeneration                 - abstract class adding offset array behavior

//   - TenuredGeneration             - tenured (old object) space (markSweepCompact)

//   - ConcurrentMarkSweepGeneration - Mostly Concurrent Mark Sweep Generation

//                                       (Detlefs-Printezis refinement of

//                                       Boehm-Demers-Schenker)

//

// The system configurations currently allowed are:

//

//   DefNewGeneration + TenuredGeneration

//

//   ParNewGeneration + ConcurrentMarkSweepGeneration

//

class DefNewGeneration;

class GCMemoryManager;

class GenerationSpec;

class CompactibleSpace;

class ContiguousSpace;

class CompactPoint;

class OopsInGenClosure;

class OopClosure;

class ScanClosure;

class FastScanClosure;

class GenCollectedHeap;

class GCStats;

// A "ScratchBlock" represents a block of memory in one generation usable by

// another.  It represents "num_words" free words, starting at and including

// the address of "this".

struct ScratchBlock {

  ScratchBlock* next;

  size_t num_words;

  HeapWord scratch_space[1];  // Actually, of size "num_words-2" (assuming

                              // first two fields are word-sized.)

};

class Generation: public CHeapObj<mtGC> {

  friend class VMStructs;

 private:

  jlong _time_of_last_gc; // time when last gc on this generation happened (ms)

  MemRegion _prev_used_region; // for collectors that want to "remember" a value for

                               // used region at some specific point during collection.

  GCMemoryManager* _gc_manager;

 protected:

  // Minimum and maximum addresses for memory reserved (not necessarily

  // committed) for generation.

  // Used by card marking code. Must not overlap with address ranges of

  // other generations.

  MemRegion _reserved;

  // Memory area reserved for generation

  VirtualSpace _virtual_space;

  // ("Weak") Reference processing support

  SpanSubjectToDiscoveryClosure _span_based_discoverer;

  ReferenceProcessor* _ref_processor;

  // Performance Counters

  CollectorCounters* _gc_counters;

  // Statistics for garbage collection

  GCStats* _gc_stats;

  // Initialize the generation.

  Generation(ReservedSpace rs, size_t initial_byte_size);

  // Apply "cl->do_oop" to (the address of) (exactly) all the ref fields in

  // "sp" that point into younger generations.

  // The iteration is only over objects allocated at the start of the

  // iterations; objects allocated as a result of applying the closure are

  // not included.

  void younger_refs_in_space_iterate(Space* sp, OopsInGenClosure* cl, uint n_threads);

 public:

  // The set of possible generation kinds.

  enum Name {

    DefNew,

    ParNew,

    MarkSweepCompact,

    ConcurrentMarkSweep,

    Other

  };

  enum SomePublicConstants {

    // Generations are GenGrain-aligned and have size that are multiples of

    // GenGrain.

    // Note: on ARM we add 1 bit for card_table_base to be properly aligned

    // (we expect its low byte to be zero - see implementation of post_barrier)

    LogOfGenGrain = 16 ARM32_ONLY(+1),

    GenGrain = 1 << LogOfGenGrain

  };

  // allocate and initialize ("weak") refs processing support

  virtual void ref_processor_init();

  void set_ref_processor(ReferenceProcessor* rp) {

    assert(_ref_processor == NULL, "clobbering existing _ref_processor");

    _ref_processor = rp;

  }

  virtual Generation::Name kind() { return Generation::Other; }

  // This properly belongs in the collector, but for now this

  // will do.

  virtual bool refs_discovery_is_atomic() const { return true;  }

  virtual bool refs_discovery_is_mt()     const { return false; }

  // Space inquiries (results in bytes)

  size_t initial_size();

  virtual size_t capacity() const = 0;  // The maximum number of object bytes the

                                        // generation can currently hold.

  virtual size_t used() const = 0;      // The number of used bytes in the gen.

  virtual size_t free() const = 0;      // The number of free bytes in the gen.

  // Support for java.lang.Runtime.maxMemory(); see CollectedHeap.

  // Returns the total number of bytes  available in a generation

  // for the allocation of objects.

  virtual size_t max_capacity() const;

  // If this is a young generation, the maximum number of bytes that can be

  // allocated in this generation before a GC is triggered.

  virtual size_t capacity_before_gc() const { return 0; }

  // The largest number of contiguous free bytes in the generation,

  // including expansion  (Assumes called at a safepoint.)

  virtual size_t contiguous_available() const = 0;

  // The largest number of contiguous free bytes in this or any higher generation.

  virtual size_t max_contiguous_available() const;

  // Returns true if promotions of the specified amount are

  // likely to succeed without a promotion failure.

  // Promotion of the full amount is not guaranteed but

  // might be attempted in the worst case.

  virtual bool promotion_attempt_is_safe(size_t max_promotion_in_bytes) const;

  // For a non-young generation, this interface can be used to inform a

  // generation that a promotion attempt into that generation failed.

  // Typically used to enable diagnostic output for post-mortem analysis,

  // but other uses of the interface are not ruled out.

  virtual void promotion_failure_occurred() { /* does nothing */ }

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

  // in the generation without triggering any collection or expansion

  // activity.  It is "unsafe" because no locks are taken; the result

  // should be treated as an approximation, not a guarantee, for use in

  // heuristic resizing decisions.

  virtual size_t unsafe_max_alloc_nogc() const = 0;

  // Returns true if this generation cannot be expanded further

  // without a GC. Override as appropriate.

  virtual bool is_maximal_no_gc() const {

    return _virtual_space.uncommitted_size() == 0;

  }

  MemRegion reserved() const { return _reserved; }

  // Returns a region guaranteed to contain all the objects in the

  // generation.

  virtual MemRegion used_region() const { return _reserved; }

  MemRegion prev_used_region() const { return _prev_used_region; }

  virtual void  save_used_region()   { _prev_used_region = used_region(); }

  // Returns "TRUE" iff "p" points into the committed areas in the generation.

  // For some kinds of generations, this may be an expensive operation.

  // To avoid performance problems stemming from its inadvertent use in

  // product jvm's, we restrict its use to assertion checking or

  // verification only.

  virtual bool is_in(const void* p) const;

  /* Returns "TRUE" iff "p" points into the reserved area of the generation. */

  bool is_in_reserved(const void* p) const {

    return _reserved.contains(p);

  }

  // If some space in the generation contains the given "addr", return a

  // pointer to that space, else return "NULL".

  virtual Space* space_containing(const void* addr) const;

  // Iteration - do not use for time critical operations

  virtual void space_iterate(SpaceClosure* blk, bool usedOnly = false) = 0;

  // Returns the first space, if any, in the generation that can participate

  // in compaction, or else "NULL".

  virtual CompactibleSpace* first_compaction_space() const = 0;

  // Returns "true" iff this generation should be used to allocate an

  // object of the given size.  Young generations might

  // wish to exclude very large objects, for example, since, if allocated

  // often, they would greatly increase the frequency of young-gen

  // collection.

  virtual bool should_allocate(size_t word_size, bool is_tlab) {

    bool result = false;

    size_t overflow_limit = (size_t)1 << (BitsPerSize_t - LogHeapWordSize);

    if (!is_tlab || supports_tlab_allocation()) {

      result = (word_size > 0) && (word_size < overflow_limit);

    }

    return result;

  }

  // Allocate and returns a block of the requested size, or returns "NULL".

  // Assumes the caller has done any necessary locking.

  virtual HeapWord* allocate(size_t word_size, bool is_tlab) = 0;

  // Like "allocate", but performs any necessary locking internally.

  virtual HeapWord* par_allocate(size_t word_size, bool is_tlab) = 0;

  // Some generation may offer a region for shared, contiguous allocation,

  // via inlined code (by exporting the address of the top and end fields

  // defining the extent of the contiguous allocation region.)

  // This function returns "true" iff the heap supports this kind of

  // allocation.  (More precisely, this means the style of allocation that

  // increments *top_addr()" with a CAS.) (Default is "no".)

  // A generation that supports this allocation style must use lock-free

  // allocation for *all* allocation, since there are times when lock free

  // allocation will be concurrent with plain "allocate" calls.

  virtual bool supports_inline_contig_alloc() const { return false; }

  // These functions return the addresses of the fields that define the

  // boundaries of the contiguous allocation area.  (These fields should be

  // physically near to one another.)

  virtual HeapWord* volatile* top_addr() const { return NULL; }

  virtual HeapWord** end_addr() const { return NULL; }

  // Thread-local allocation buffers

  virtual bool supports_tlab_allocation() const { return false; }

  virtual size_t tlab_capacity() const {

    guarantee(false, "Generation doesn't support thread local allocation buffers");

    return 0;

  }

  virtual size_t tlab_used() const {

    guarantee(false, "Generation doesn't support thread local allocation buffers");

    return 0;

  }

  virtual size_t unsafe_max_tlab_alloc() const {

    guarantee(false, "Generation doesn't support thread local allocation buffers");

    return 0;

  }

  // "obj" is the address of an object in a younger generation.  Allocate space

  // for "obj" in the current (or some higher) generation, and copy "obj" into

  // the newly allocated space, if possible, returning the result (or NULL if

  // the allocation failed).

  //

  // The "obj_size" argument is just obj->size(), passed along so the caller can

  // avoid repeating the virtual call to retrieve it.

  virtual oop promote(oop obj, size_t obj_size);

  // Thread "thread_num" (0 <= i < ParalleGCThreads) wants to promote

  // object "obj", whose original mark word was "m", and whose size is

  // "word_sz".  If possible, allocate space for "obj", copy obj into it

  // (taking care to copy "m" into the mark word when done, since the mark

  // word of "obj" may have been overwritten with a forwarding pointer, and

  // also taking care to copy the klass pointer *last*.  Returns the new

  // object if successful, or else NULL.

  virtual oop par_promote(int thread_num, oop obj, markOop m, size_t word_sz);

  // Informs the current generation that all par_promote_alloc's in the

  // collection have been completed; any supporting data structures can be

  // reset.  Default is to do nothing.

  virtual void par_promote_alloc_done(int thread_num) {}

  // Informs the current generation that all oop_since_save_marks_iterates

  // performed by "thread_num" in the current collection, if any, have been

  // completed; any supporting data structures can be reset.  Default is to

  // do nothing.

  virtual void par_oop_since_save_marks_iterate_done(int thread_num) {}

  // Returns "true" iff collect() should subsequently be called on this

  // this generation. See comment below.

  // This is a generic implementation which can be overridden.

  //

  // Note: in the current (1.4) implementation, when genCollectedHeap's

  // incremental_collection_will_fail flag is set, all allocations are

  // slow path (the only fast-path place to allocate is DefNew, which

  // will be full if the flag is set).

  // Thus, older generations which collect younger generations should

  // test this flag and collect if it is set.

  virtual bool should_collect(bool   full,

                              size_t word_size,

                              bool   is_tlab) {

    return (full || should_allocate(word_size, is_tlab));

  }

  // Returns true if the collection is likely to be safely

  // completed. Even if this method returns true, a collection

  // may not be guaranteed to succeed, and the system should be

  // able to safely unwind and recover from that failure, albeit

  // at some additional cost.

  virtual bool collection_attempt_is_safe() {

    guarantee(false, "Are you sure you want to call this method?");

    return true;

  }

  // Perform a garbage collection.

  // If full is true attempt a full garbage collection of this generation.

  // Otherwise, attempting to (at least) free enough space to support an

  // allocation of the given "word_size".

  virtual void collect(bool   full,

                       bool   clear_all_soft_refs,

                       size_t word_size,

                       bool   is_tlab) = 0;

  // Perform a heap collection, attempting to create (at least) enough

  // space to support an allocation of the given "word_size".  If

  // successful, perform the allocation and return the resulting

  // "oop" (initializing the allocated block). If the allocation is

  // still unsuccessful, return "NULL".

  virtual HeapWord* expand_and_allocate(size_t word_size,

                                        bool is_tlab,

                                        bool parallel = false) = 0;

  // Some generations may require some cleanup or preparation actions before

  // allowing a collection.  The default is to do nothing.

  virtual void gc_prologue(bool full) {}

  // Some generations may require some cleanup actions after a collection.

  // The default is to do nothing.

  virtual void gc_epilogue(bool full) {}

  // Save the high water marks for the used space in a generation.

  virtual void record_spaces_top() {}

  // Some generations may need to be "fixed-up" after some allocation

  // activity to make them parsable again. The default is to do nothing.

  virtual void ensure_parsability() {}

  // Time (in ms) when we were last collected or now if a collection is

  // in progress.

  virtual jlong time_of_last_gc(jlong now) {

    // Both _time_of_last_gc and now are set using a time source

    // that guarantees monotonically non-decreasing values provided

    // the underlying platform provides such a source. So we still

    // have to guard against non-monotonicity.

    NOT_PRODUCT(

      if (now < _time_of_last_gc) {

        log_warning(gc)("time warp: " JLONG_FORMAT " to " JLONG_FORMAT, _time_of_last_gc, now);

      }

    )

    return _time_of_last_gc;

  }

  virtual void update_time_of_last_gc(jlong now)  {

    _time_of_last_gc = now;

  }

  // Generations may keep statistics about collection. This method

  // updates those statistics. current_generation is the generation

  // that was most recently collected. This allows the generation to

  // decide what statistics are valid to collect. For example, the

  // generation can decide to gather the amount of promoted data if

  // the collection of the young generation has completed.

  GCStats* gc_stats() const { return _gc_stats; }

  virtual void update_gc_stats(Generation* current_generation, bool full) {}

#if INCLUDE_SERIALGC

  // Mark sweep support phase2

  virtual void prepare_for_compaction(CompactPoint* cp);

  // Mark sweep support phase3

  virtual void adjust_pointers();

  // Mark sweep support phase4

  virtual void compact();

  virtual void post_compact() { ShouldNotReachHere(); }

#endif

  // Support for CMS's rescan. In this general form we return a pointer

  // to an abstract object that can be used, based on specific previously

  // decided protocols, to exchange information between generations,

  // information that may be useful for speeding up certain types of

  // garbage collectors. A NULL value indicates to the client that

  // no data recording is expected by the provider. The data-recorder is

  // expected to be GC worker thread-local, with the worker index

  // indicated by "thr_num".

  virtual void* get_data_recorder(int thr_num) { return NULL; }

  virtual void sample_eden_chunk() {}

  // Some generations may require some cleanup actions before allowing

  // a verification.

  virtual void prepare_for_verify() {}

  // Accessing "marks".

  // This function gives a generation a chance to note a point between

  // collections.  For example, a contiguous generation might note the

  // beginning allocation point post-collection, which might allow some later

  // operations to be optimized.

  virtual void save_marks() {}

  // This function allows generations to initialize any "saved marks".  That

  // is, should only be called when the generation is empty.

  virtual void reset_saved_marks() {}

  // This function is "true" iff any no allocations have occurred in the

  // generation since the last call to "save_marks".

  virtual bool no_allocs_since_save_marks() = 0;

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

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

  // the target is not the requestor, no gc actions will be required

  // of the target.  The requestor promises to allocate no more than

  // "max_alloc_words" in the target generation (via promotion say,

  // if the requestor is a young generation and the target is older).

  // If the target generation can provide any scratch space, it adds

  // it to "list", leaving "list" pointing to the head of the

  // augmented list.  The default is to offer no space.

  virtual void contribute_scratch(ScratchBlock*& list, Generation* requestor,

                                  size_t max_alloc_words) {}

  // Give each generation an opportunity to do clean up for any

  // contributed scratch.

  virtual void reset_scratch() {}

  // When an older generation has been collected, and perhaps resized,

  // this method will be invoked on all younger generations (from older to

  // younger), allowing them to resize themselves as appropriate.

  virtual void compute_new_size() = 0;

  // Printing

  virtual const char* name() const = 0;

  virtual const char* short_name() const = 0;

  // Reference Processing accessor

  ReferenceProcessor* const ref_processor() { return _ref_processor; }

  // Iteration.

  // Iterate over all the ref-containing fields of all objects in the

  // generation, calling "cl.do_oop" on each.

  virtual void oop_iterate(OopIterateClosure* cl);

  // Iterate over all objects in the generation, calling "cl.do_object" on

  // each.

  virtual void object_iterate(ObjectClosure* cl);

  // Iterate over all safe objects in the generation, calling "cl.do_object" on

  // each.  An object is safe if its references point to other objects in

  // the heap.  This defaults to object_iterate() unless overridden.

  virtual void safe_object_iterate(ObjectClosure* cl);

  // Apply "cl->do_oop" to (the address of) all and only all the ref fields

  // in the current generation that contain pointers to objects in younger

  // generations. Objects allocated since the last "save_marks" call are

  // excluded.

  virtual void younger_refs_iterate(OopsInGenClosure* cl, uint n_threads) = 0;

  // Inform a generation that it longer contains references to objects

  // in any younger generation.    [e.g. Because younger gens are empty,

  // clear the card table.]

  virtual void clear_remembered_set() { }

  // Inform a generation that some of its objects have moved.  [e.g. The

  // generation's spaces were compacted, invalidating the card table.]

  virtual void invalidate_remembered_set() { }

  // Block abstraction.

  // 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.

  virtual size_t block_size(const HeapWord* addr) const ;

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