view src/share/vm/utilities/bitMap.hpp @ 2533:842b840e67db

7046558: G1: concurrent marking optimizations Summary: Some optimizations to improve the concurrent marking phase: specialize the main oop closure, make sure a few methods in the fast path are properly inlined, a few more bits and pieces, and some cosmetic fixes. Reviewed-by: stefank, johnc
author tonyp
date Tue, 14 Jun 2011 10:33:43 -0400
parents f95d63e2154a
children 2a0172480595
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 * Copyright (c) 1997, 2011, Oracle and/or its affiliates. All rights reserved.
 * 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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 * questions.


#include "memory/allocation.hpp"
#include "utilities/top.hpp"

// Forward decl;
class BitMapClosure;

// Operations for bitmaps represented as arrays of unsigned integers.
// Bit offsets are numbered from 0 to size-1.

  friend class BitMap2D;

  typedef size_t idx_t;         // Type used for bit and word indices.
  typedef uintptr_t bm_word_t;  // Element type of array that represents
                                // the bitmap.

  // Hints for range sizes.
  typedef enum {
    unknown_range, small_range, large_range
  } RangeSizeHint;

  bm_word_t* _map;     // First word in bitmap
  idx_t      _size;    // Size of bitmap (in bits)

  // Puts the given value at the given offset, using resize() to size
  // the bitmap appropriately if needed using factor-of-two expansion.
  void at_put_grow(idx_t index, bool value);

  // Return the position of bit within the word that contains it (e.g., if
  // bitmap words are 32 bits, return a number 0 <= n <= 31).
  static idx_t bit_in_word(idx_t bit) { return bit & (BitsPerWord - 1); }

  // Return a mask that will select the specified bit, when applied to the word
  // containing the bit.
  static bm_word_t bit_mask(idx_t bit) { return (bm_word_t)1 << bit_in_word(bit); }

  // Return the index of the word containing the specified bit.
  static idx_t word_index(idx_t bit)  { return bit >> LogBitsPerWord; }

  // Return the bit number of the first bit in the specified word.
  static idx_t bit_index(idx_t word)  { return word << LogBitsPerWord; }

  // Return the array of bitmap words, or a specific word from it.
  bm_word_t* map() const           { return _map; }
  bm_word_t  map(idx_t word) const { return _map[word]; }

  // Return a pointer to the word containing the specified bit.
  bm_word_t* word_addr(idx_t bit) const { return map() + word_index(bit); }

  // Set a word to a specified value or to all ones; clear a word.
  void set_word  (idx_t word, bm_word_t val) { _map[word] = val; }
  void set_word  (idx_t word)            { set_word(word, ~(uintptr_t)0); }
  void clear_word(idx_t word)            { _map[word] = 0; }

  // Utilities for ranges of bits.  Ranges are half-open [beg, end).

  // Ranges within a single word.
  bm_word_t inverted_bit_mask_for_range(idx_t beg, idx_t end) const;
  void  set_range_within_word      (idx_t beg, idx_t end);
  void  clear_range_within_word    (idx_t beg, idx_t end);
  void  par_put_range_within_word  (idx_t beg, idx_t end, bool value);

  // Ranges spanning entire words.
  void      set_range_of_words         (idx_t beg, idx_t end);
  void      clear_range_of_words       (idx_t beg, idx_t end);
  void      set_large_range_of_words   (idx_t beg, idx_t end);
  void      clear_large_range_of_words (idx_t beg, idx_t end);

  // The index of the first full word in a range.
  idx_t word_index_round_up(idx_t bit) const;

  // Verification.
  inline void verify_index(idx_t index) const NOT_DEBUG_RETURN;
  inline void verify_range(idx_t beg_index, idx_t end_index) const

  // Statistics.
  static idx_t* _pop_count_table;
  static void init_pop_count_table();
  static idx_t num_set_bits(bm_word_t w);
  static idx_t num_set_bits_from_table(unsigned char c);


  // Constructs a bitmap with no map, and size 0.
  BitMap() : _map(NULL), _size(0) {}

  // Constructs a bitmap with the given map and size.
  BitMap(bm_word_t* map, idx_t size_in_bits);

  // Constructs an empty bitmap of the given size (that is, this clears the
  // new bitmap).  Allocates the map array in resource area if
  // "in_resource_area" is true, else in the C heap.
  BitMap(idx_t size_in_bits, bool in_resource_area = true);

  // Set the map and size.
  void set_map(bm_word_t* map)      { _map = map; }
  void set_size(idx_t size_in_bits) { _size = size_in_bits; }

  // Allocates necessary data structure, either in the resource area
  // or in the C heap, as indicated by "in_resource_area."
  // Preserves state currently in bit map by copying data.
  // Zeros any newly-addressable bits.
  // If "in_resource_area" is false, frees the current map.
  // (Note that this assumes that all calls to "resize" on the same BitMap
  // use the same value for "in_resource_area".)
  void resize(idx_t size_in_bits, bool in_resource_area = true);

  // Accessing
  idx_t size() const                    { return _size; }
  idx_t size_in_words() const           {
    return word_index(size() + BitsPerWord - 1);

  bool at(idx_t index) const {
    return (*word_addr(index) & bit_mask(index)) != 0;

  // Align bit index up or down to the next bitmap word boundary, or check
  // alignment.
  static idx_t word_align_up(idx_t bit) {
    return align_size_up(bit, BitsPerWord);
  static idx_t word_align_down(idx_t bit) {
    return align_size_down(bit, BitsPerWord);
  static bool is_word_aligned(idx_t bit) {
    return word_align_up(bit) == bit;

  // Set or clear the specified bit.
  inline void set_bit(idx_t bit);
  inline void clear_bit(idx_t bit);

  // Atomically set or clear the specified bit.
  inline bool par_set_bit(idx_t bit);
  inline bool par_clear_bit(idx_t bit);

  // Put the given value at the given offset. The parallel version
  // will CAS the value into the bitmap and is quite a bit slower.
  // The parallel version also returns a value indicating if the
  // calling thread was the one that changed the value of the bit.
  void at_put(idx_t index, bool value);
  bool par_at_put(idx_t index, bool value);

  // Update a range of bits.  Ranges are half-open [beg, end).
  void set_range   (idx_t beg, idx_t end);
  void clear_range (idx_t beg, idx_t end);
  void set_large_range   (idx_t beg, idx_t end);
  void clear_large_range (idx_t beg, idx_t end);
  void at_put_range(idx_t beg, idx_t end, bool value);
  void par_at_put_range(idx_t beg, idx_t end, bool value);
  void at_put_large_range(idx_t beg, idx_t end, bool value);
  void par_at_put_large_range(idx_t beg, idx_t end, bool value);

  // Update a range of bits, using a hint about the size.  Currently only
  // inlines the predominant case of a 1-bit range.  Works best when hint is a
  // compile-time constant.
  void set_range(idx_t beg, idx_t end, RangeSizeHint hint);
  void clear_range(idx_t beg, idx_t end, RangeSizeHint hint);
  void par_set_range(idx_t beg, idx_t end, RangeSizeHint hint);
  void par_clear_range  (idx_t beg, idx_t end, RangeSizeHint hint);

  // It performs the union operation between subsets of equal length
  // of two bitmaps (the target bitmap of the method and the
  // from_bitmap) and stores the result to the target bitmap.  The
  // from_start_index represents the first bit index of the subrange
  // of the from_bitmap.  The to_start_index is the equivalent of the
  // target bitmap. Both indexes should be word-aligned, i.e. they
  // should correspond to the first bit on a bitmap word (it's up to
  // the caller to ensure this; the method does check it).  The length
  // of the subset is specified with word_num and it is in number of
  // bitmap words. The caller should ensure that this is at least 2
  // (smaller ranges are not support to save extra checks).  Again,
  // this is checked in the method.
  // Atomicity concerns: it is assumed that any contention on the
  // target bitmap with other threads will happen on the first and
  // last words; the ones in between will be "owned" exclusively by
  // the calling thread and, in fact, they will already be 0. So, the
  // method performs a CAS on the first word, copies the next
  // word_num-2 words, and finally performs a CAS on the last word.
  void mostly_disjoint_range_union(BitMap* from_bitmap,
                                   idx_t   from_start_index,
                                   idx_t   to_start_index,
                                   size_t  word_num);

  // Clearing
  void clear_large();
  inline void clear();

  // Iteration support.  Returns "true" if the iteration completed, false
  // if the iteration terminated early (because the closure "blk" returned
  // false).
  bool iterate(BitMapClosure* blk, idx_t leftIndex, idx_t rightIndex);
  bool iterate(BitMapClosure* blk) {
    // call the version that takes an interval
    return iterate(blk, 0, size());

  // Looking for 1's and 0's at indices equal to or greater than "l_index",
  // stopping if none has been found before "r_index", and returning
  // "r_index" (which must be at most "size") in that case.
  idx_t get_next_one_offset_inline (idx_t l_index, idx_t r_index) const;
  idx_t get_next_zero_offset_inline(idx_t l_index, idx_t r_index) const;

  // Like "get_next_one_offset_inline", except requires that "r_index" is
  // aligned to bitsizeof(bm_word_t).
  idx_t get_next_one_offset_inline_aligned_right(idx_t l_index,
                                                        idx_t r_index) const;

  // Non-inline versionsof the above.
  idx_t get_next_one_offset (idx_t l_index, idx_t r_index) const;
  idx_t get_next_zero_offset(idx_t l_index, idx_t r_index) const;

  idx_t get_next_one_offset(idx_t offset) const {
    return get_next_one_offset(offset, size());
  idx_t get_next_zero_offset(idx_t offset) const {
    return get_next_zero_offset(offset, size());

  // Returns the number of bits set in the bitmap.
  idx_t count_one_bits() const;

  // Set operations.
  void set_union(BitMap bits);
  void set_difference(BitMap bits);
  void set_intersection(BitMap bits);
  // Returns true iff "this" is a superset of "bits".
  bool contains(const BitMap bits) const;
  // Returns true iff "this and "bits" have a non-empty intersection.
  bool intersects(const BitMap bits) const;

  // Returns result of whether this map changed
  // during the operation
  bool set_union_with_result(BitMap bits);
  bool set_difference_with_result(BitMap bits);
  bool set_intersection_with_result(BitMap bits);

  // Requires the submap of "bits" starting at offset to be at least as
  // large as "this".  Modifies "this" to be the intersection of its
  // current contents and the submap of "bits" starting at "offset" of the
  // same length as "this."
  // (For expedience, currently requires the offset to be aligned to the
  // bitsize of a uintptr_t.  This should go away in the future though it
  // will probably remain a good case to optimize.)
  void set_intersection_at_offset(BitMap bits, idx_t offset);

  void set_from(BitMap bits);

  bool is_same(BitMap bits);

  // Test if all bits are set or cleared
  bool is_full() const;
  bool is_empty() const;

#ifndef PRODUCT
  // Printing
  void print_on(outputStream* st) const;

// Convenience class wrapping BitMap which provides multiple bits per slot.
  typedef BitMap::idx_t idx_t;          // Type used for bit and word indices.
  typedef BitMap::bm_word_t bm_word_t;  // Element type of array that
                                        // represents the bitmap.
  BitMap _map;
  idx_t  _bits_per_slot;

  idx_t bit_index(idx_t slot_index, idx_t bit_within_slot_index) const {
    return slot_index * _bits_per_slot + bit_within_slot_index;

  void verify_bit_within_slot_index(idx_t index) const {
    assert(index < _bits_per_slot, "bit_within_slot index out of bounds");

  // Construction. bits_per_slot must be greater than 0.
  BitMap2D(bm_word_t* map, idx_t size_in_slots, idx_t bits_per_slot);

  // Allocates necessary data structure in resource area. bits_per_slot must be greater than 0.
  BitMap2D(idx_t size_in_slots, idx_t bits_per_slot);

  idx_t size_in_bits() {
    return _map.size();

  // Returns number of full slots that have been allocated
  idx_t size_in_slots() {
    // Round down
    return _map.size() / _bits_per_slot;

  bool is_valid_index(idx_t slot_index, idx_t bit_within_slot_index) {
    return (bit_index(slot_index, bit_within_slot_index) < size_in_bits());

  bool at(idx_t slot_index, idx_t bit_within_slot_index) const {
    return, bit_within_slot_index));

  void set_bit(idx_t slot_index, idx_t bit_within_slot_index) {
    _map.set_bit(bit_index(slot_index, bit_within_slot_index));

  void clear_bit(idx_t slot_index, idx_t bit_within_slot_index) {
    _map.clear_bit(bit_index(slot_index, bit_within_slot_index));

  void at_put(idx_t slot_index, idx_t bit_within_slot_index, bool value) {
    _map.at_put(bit_index(slot_index, bit_within_slot_index), value);

  void at_put_grow(idx_t slot_index, idx_t bit_within_slot_index, bool value) {
    _map.at_put_grow(bit_index(slot_index, bit_within_slot_index), value);

  void clear();

// Closure for iterating over BitMaps

class BitMapClosure VALUE_OBJ_CLASS_SPEC {
  // Callback when bit in map is set.  Should normally return "true";
  // return of false indicates that the bitmap iteration should terminate.
  virtual bool do_bit(BitMap::idx_t offset) = 0;