/*

 * Copyright (c) 2000, 2018, 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_CARDTABLEMODREFBS_HPP

#define SHARE_VM_GC_SHARED_CARDTABLEMODREFBS_HPP

#include "gc/shared/modRefBarrierSet.hpp"

#include "utilities/align.hpp"

// This kind of "BarrierSet" allows a "CollectedHeap" to detect and

// enumerate ref fields that have been modified (since the last

// enumeration.)

// As it currently stands, this barrier is *imprecise*: when a ref field in

// an object "o" is modified, the card table entry for the card containing

// the head of "o" is dirtied, not necessarily the card containing the

// modified field itself.  For object arrays, however, the barrier *is*

// precise; only the card containing the modified element is dirtied.

// Closures used to scan dirty cards should take these

// considerations into account.

class CardTableModRefBS: public ModRefBarrierSet {

  // Some classes get to look at some private stuff.

  friend class VMStructs;

 protected:

  enum CardValues {

    clean_card                  = -1,

    // The mask contains zeros in places for all other values.

    clean_card_mask             = clean_card - 31,

    dirty_card                  =  0,

    precleaned_card             =  1,

    claimed_card                =  2,

    deferred_card               =  4,

    last_card                   =  8,

    CT_MR_BS_last_reserved      = 16

  };

  // Used in support of ReduceInitialCardMarks; only consulted if COMPILER2

  // or INCLUDE_JVMCI is being used

  bool _defer_initial_card_mark;

  // a word's worth (row) of clean card values

  static const intptr_t clean_card_row = (intptr_t)(-1);

  // The declaration order of these const fields is important; see the

  // constructor before changing.

  const MemRegion _whole_heap;       // the region covered by the card table

  size_t          _guard_index;      // index of very last element in the card

                                     // table; it is set to a guard value

                                     // (last_card) and should never be modified

  size_t          _last_valid_index; // index of the last valid element

  const size_t    _page_size;        // page size used when mapping _byte_map

  size_t          _byte_map_size;    // in bytes

  jbyte*          _byte_map;         // the card marking array

  // Some barrier sets create tables whose elements correspond to parts of

  // the heap; the CardTableModRefBS is an example.  Such barrier sets will

  // normally reserve space for such tables, and commit parts of the table

  // "covering" parts of the heap that are committed. At most one covered

  // region per generation is needed.

  static const int _max_covered_regions = 2;

  int _cur_covered_regions;

  // The covered regions should be in address order.

  MemRegion* _covered;

  // The committed regions correspond one-to-one to the covered regions.

  // They represent the card-table memory that has been committed to service

  // the corresponding covered region.  It may be that committed region for

  // one covered region corresponds to a larger region because of page-size

  // roundings.  Thus, a committed region for one covered region may

  // actually extend onto the card-table space for the next covered region.

  MemRegion* _committed;

  // The last card is a guard card, and we commit the page for it so

  // we can use the card for verification purposes. We make sure we never

  // uncommit the MemRegion for that page.

  MemRegion _guard_region;

  inline size_t compute_byte_map_size();

  // Finds and return the index of the region, if any, to which the given

  // region would be contiguous.  If none exists, assign a new region and

  // returns its index.  Requires that no more than the maximum number of

  // covered regions defined in the constructor are ever in use.

  int find_covering_region_by_base(HeapWord* base);

  // Same as above, but finds the region containing the given address

  // instead of starting at a given base address.

  int find_covering_region_containing(HeapWord* addr);

  // Resize one of the regions covered by the remembered set.

  virtual void resize_covered_region(MemRegion new_region);

  // Returns the leftmost end of a committed region corresponding to a

  // covered region before covered region "ind", or else "NULL" if "ind" is

  // the first covered region.

  HeapWord* largest_prev_committed_end(int ind) const;

  // Returns the part of the region mr that doesn't intersect with

  // any committed region other than self.  Used to prevent uncommitting

  // regions that are also committed by other regions.  Also protects

  // against uncommitting the guard region.

  MemRegion committed_unique_to_self(int self, MemRegion mr) const;

  // Mapping from address to card marking array entry

  jbyte* byte_for(const void* p) const {

    assert(_whole_heap.contains(p),

           "Attempt to access p = " PTR_FORMAT " out of bounds of "

           " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",

           p2i(p), p2i(_whole_heap.start()), p2i(_whole_heap.end()));

    jbyte* result = &byte_map_base[uintptr_t(p) >> card_shift];

    assert(result >= _byte_map && result < _byte_map + _byte_map_size,

           "out of bounds accessor for card marking array");

    return result;

  }

  // The card table byte one after the card marking array

  // entry for argument address. Typically used for higher bounds

  // for loops iterating through the card table.

  jbyte* byte_after(const void* p) const {

    return byte_for(p) + 1;

  }

  // Dirty the bytes corresponding to "mr" (not all of which must be

  // covered.)

  void dirty_MemRegion(MemRegion mr);

  // Clear (to clean_card) the bytes entirely contained within "mr" (not

  // all of which must be covered.)

  void clear_MemRegion(MemRegion mr);

 public:

  // Constants

  enum SomePublicConstants {

    card_shift                  = 9,

    card_size                   = 1 << card_shift,

    card_size_in_words          = card_size / sizeof(HeapWord)

  };

  static int clean_card_val()      { return clean_card; }

  static int clean_card_mask_val() { return clean_card_mask; }

  static int dirty_card_val()      { return dirty_card; }

  static int claimed_card_val()    { return claimed_card; }

  static int precleaned_card_val() { return precleaned_card; }

  static int deferred_card_val()   { return deferred_card; }

  virtual void initialize();

  // *** Barrier set functions.

  // Initialization utilities; covered_words is the size of the covered region

  // in, um, words.

  inline size_t cards_required(size_t covered_words) {

    // Add one for a guard card, used to detect errors.

    const size_t words = align_up(covered_words, card_size_in_words);

    return words / card_size_in_words + 1;

  }

 protected:

  CardTableModRefBS(MemRegion whole_heap, const BarrierSet::FakeRtti& fake_rtti);

  ~CardTableModRefBS();

 public:

  void write_region(MemRegion mr) {

    dirty_MemRegion(mr);

  }

 protected:

  void write_ref_array_work(MemRegion mr) {

    dirty_MemRegion(mr);

  }

 public:

  bool is_aligned(HeapWord* addr) {

    return is_card_aligned(addr);

  }

  // *** Card-table-barrier-specific things.

  // Record a reference update. Note that these versions are precise!

  // The scanning code has to handle the fact that the write barrier may be

  // either precise or imprecise. We make non-virtual inline variants of

  // these functions here for performance.

  template <DecoratorSet decorators, typename T>

  void write_ref_field_post(T* field, oop newVal);

  // These are used by G1, when it uses the card table as a temporary data

  // structure for card claiming.

  bool is_card_dirty(size_t card_index) {

    return _byte_map[card_index] == dirty_card_val();

  }

  void mark_card_dirty(size_t card_index) {

    _byte_map[card_index] = dirty_card_val();

  }

  bool is_card_clean(size_t card_index) {

    return _byte_map[card_index] == clean_card_val();

  }

  // Card marking array base (adjusted for heap low boundary)

  // This would be the 0th element of _byte_map, if the heap started at 0x0.

  // But since the heap starts at some higher address, this points to somewhere

  // before the beginning of the actual _byte_map.

  jbyte* byte_map_base;

  // Return true if "p" is at the start of a card.

  bool is_card_aligned(HeapWord* p) {

    jbyte* pcard = byte_for(p);

    return (addr_for(pcard) == p);

  }

  HeapWord* align_to_card_boundary(HeapWord* p) {

    jbyte* pcard = byte_for(p + card_size_in_words - 1);

    return addr_for(pcard);

  }

  // The kinds of precision a CardTableModRefBS may offer.

  enum PrecisionStyle {

    Precise,

    ObjHeadPreciseArray

  };

  // Tells what style of precision this card table offers.

  PrecisionStyle precision() {

    return ObjHeadPreciseArray; // Only one supported for now.

  }

  // ModRefBS functions.

  virtual void invalidate(MemRegion mr);

  void clear(MemRegion mr);

  void dirty(MemRegion mr);

  // *** Card-table-RemSet-specific things.

  static uintx ct_max_alignment_constraint();

  // Apply closure "cl" to the dirty cards containing some part of

  // MemRegion "mr".

  void dirty_card_iterate(MemRegion mr, MemRegionClosure* cl);

  // Return the MemRegion corresponding to the first maximal run

  // of dirty cards lying completely within MemRegion mr.

  // If reset is "true", then sets those card table entries to the given

  // value.

  MemRegion dirty_card_range_after_reset(MemRegion mr, bool reset,

                                         int reset_val);

  // Provide read-only access to the card table array.

  const jbyte* byte_for_const(const void* p) const {

    return byte_for(p);

  }

  const jbyte* byte_after_const(const void* p) const {

    return byte_after(p);

  }

  // Mapping from card marking array entry to address of first word

  HeapWord* addr_for(const jbyte* p) const {

    assert(p >= _byte_map && p < _byte_map + _byte_map_size,

           "out of bounds access to card marking array. p: " PTR_FORMAT

           " _byte_map: " PTR_FORMAT " _byte_map + _byte_map_size: " PTR_FORMAT,

           p2i(p), p2i(_byte_map), p2i(_byte_map + _byte_map_size));

    size_t delta = pointer_delta(p, byte_map_base, sizeof(jbyte));

    HeapWord* result = (HeapWord*) (delta << card_shift);

    assert(_whole_heap.contains(result),

           "Returning result = " PTR_FORMAT " out of bounds of "

           " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",

           p2i(result), p2i(_whole_heap.start()), p2i(_whole_heap.end()));

    return result;

  }

  // Mapping from address to card marking array index.

  size_t index_for(void* p) {

    assert(_whole_heap.contains(p),

           "Attempt to access p = " PTR_FORMAT " out of bounds of "

           " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",

           p2i(p), p2i(_whole_heap.start()), p2i(_whole_heap.end()));

    return byte_for(p) - _byte_map;

  }

  const jbyte* byte_for_index(const size_t card_index) const {

    return _byte_map + card_index;

  }

  // Print a description of the memory for the barrier set

  virtual void print_on(outputStream* st) const;

  void verify();

  void verify_guard();

  // val_equals -> it will check that all cards covered by mr equal val

  // !val_equals -> it will check that all cards covered by mr do not equal val

  void verify_region(MemRegion mr, jbyte val, bool val_equals) PRODUCT_RETURN;

  void verify_not_dirty_region(MemRegion mr) PRODUCT_RETURN;

  void verify_dirty_region(MemRegion mr) PRODUCT_RETURN;

  // ReduceInitialCardMarks

  void initialize_deferred_card_mark_barriers();

  // If the CollectedHeap was asked to defer a store barrier above,

  // this informs it to flush such a deferred store barrier to the

  // remembered set.

  void flush_deferred_card_mark_barrier(JavaThread* thread);

  // 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. If such permission

  // is granted for this heap type, the compiler promises to call

  // defer_store_barrier() below on any slow path allocation of

  // a new object for which such initializing store barriers will

  // have been elided. G1, like CMS, allows this, but should be

  // ready to provide a compensating write barrier as necessary

  // if that storage came out of a non-young region. The efficiency

  // of this implementation depends crucially on being able to

  // answer very efficiently in constant time whether a piece of

  // storage in the heap comes from a young region or not.

  // See ReduceInitialCardMarks.

  virtual bool can_elide_tlab_store_barriers() const {

    return true;

  }

  // If a compiler is eliding store barriers for TLAB-allocated objects,

  // we will be informed of a slow-path allocation by a call

  // to on_slowpath_allocation_exit() below. Such a call precedes the

  // initialization of the object itself, and no post-store-barriers will

  // be issued. Some heap types require that the barrier strictly follows

  // the initializing stores. (This is currently implemented by deferring the

  // barrier until the next slow-path allocation or gc-related safepoint.)

  // This interface answers whether a particular barrier type needs the card

  // mark to be thus strictly sequenced after the stores.

  virtual bool card_mark_must_follow_store() const = 0;

  virtual bool is_in_young(oop obj) const = 0;

  virtual void on_slowpath_allocation_exit(JavaThread* thread, oop new_obj);

  virtual void make_parsable(JavaThread* thread) { flush_deferred_card_mark_barrier(thread); }

  template <DecoratorSet decorators, typename BarrierSetT = CardTableModRefBS>

  class AccessBarrier: public ModRefBarrierSet::AccessBarrier<decorators, BarrierSetT> {};

};

template<>

struct BarrierSet::GetName<CardTableModRefBS> {

  static const BarrierSet::Name value = BarrierSet::CardTableModRef;

};

template<>

struct BarrierSet::GetType<BarrierSet::CardTableModRef> {

  typedef CardTableModRefBS type;

};

#endif // SHARE_VM_GC_SHARED_CARDTABLEMODREFBS_HPP