--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/share/vm/memory/blockOffsetTable.hpp	Sat Dec 01 00:00:00 2007 +0000
@@ -0,0 +1,500 @@
+/*
+ * Copyright 2000-2006 Sun Microsystems, Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ *
+ */
+
+// The CollectedHeap type requires subtypes to implement a method
+// "block_start".  For some subtypes, notably generational
+// systems using card-table-based write barriers, the efficiency of this
+// operation may be important.  Implementations of the "BlockOffsetArray"
+// class may be useful in providing such efficient implementations.
+//
+// BlockOffsetTable (abstract)
+//   - BlockOffsetArray (abstract)
+//     - BlockOffsetArrayNonContigSpace
+//     - BlockOffsetArrayContigSpace
+//
+
+class ContiguousSpace;
+class SerializeOopClosure;
+
+//////////////////////////////////////////////////////////////////////////
+// The BlockOffsetTable "interface"
+//////////////////////////////////////////////////////////////////////////
+class BlockOffsetTable VALUE_OBJ_CLASS_SPEC {
+  friend class VMStructs;
+protected:
+  // These members describe the region covered by the table.
+
+  // The space this table is covering.
+  HeapWord* _bottom;    // == reserved.start
+  HeapWord* _end;       // End of currently allocated region.
+
+public:
+  // Initialize the table to cover the given space.
+  // The contents of the initial table are undefined.
+  BlockOffsetTable(HeapWord* bottom, HeapWord* end):
+    _bottom(bottom), _end(end) {
+    assert(_bottom <= _end, "arguments out of order");
+  }
+
+  // Note that the committed size of the covered space may have changed,
+  // so the table size might also wish to change.
+  virtual void resize(size_t new_word_size) = 0;
+
+  virtual void set_bottom(HeapWord* new_bottom) {
+    assert(new_bottom <= _end, "new_bottom > _end");
+    _bottom = new_bottom;
+    resize(pointer_delta(_end, _bottom));
+  }
+
+  // Requires "addr" to be contained by a block, and returns the address of
+  // the start of that block.
+  virtual HeapWord* block_start_unsafe(const void* addr) const = 0;
+
+  // Returns the address of the start of the block containing "addr", or
+  // else "null" if it is covered by no block.
+  HeapWord* block_start(const void* addr) const;
+};
+
+//////////////////////////////////////////////////////////////////////////
+// One implementation of "BlockOffsetTable," the BlockOffsetArray,
+// divides the covered region into "N"-word subregions (where
+// "N" = 2^"LogN".  An array with an entry for each such subregion
+// indicates how far back one must go to find the start of the
+// chunk that includes the first word of the subregion.
+//
+// Each BlockOffsetArray is owned by a Space.  However, the actual array
+// may be shared by several BlockOffsetArrays; this is useful
+// when a single resizable area (such as a generation) is divided up into
+// several spaces in which contiguous allocation takes place.  (Consider,
+// for example, the garbage-first generation.)
+
+// Here is the shared array type.
+//////////////////////////////////////////////////////////////////////////
+// BlockOffsetSharedArray
+//////////////////////////////////////////////////////////////////////////
+class BlockOffsetSharedArray: public CHeapObj {
+  friend class BlockOffsetArray;
+  friend class BlockOffsetArrayNonContigSpace;
+  friend class BlockOffsetArrayContigSpace;
+  friend class VMStructs;
+
+ private:
+  enum SomePrivateConstants {
+    LogN = 9,
+    LogN_words = LogN - LogHeapWordSize,
+    N_bytes = 1 << LogN,
+    N_words = 1 << LogN_words
+  };
+
+  // The reserved region covered by the shared array.
+  MemRegion _reserved;
+
+  // End of the current committed region.
+  HeapWord* _end;
+
+  // Array for keeping offsets for retrieving object start fast given an
+  // address.
+  VirtualSpace _vs;
+  u_char* _offset_array;          // byte array keeping backwards offsets
+
+ protected:
+  // Bounds checking accessors:
+  // For performance these have to devolve to array accesses in product builds.
+  u_char offset_array(size_t index) const {
+    assert(index < _vs.committed_size(), "index out of range");
+    return _offset_array[index];
+  }
+  void set_offset_array(size_t index, u_char offset) {
+    assert(index < _vs.committed_size(), "index out of range");
+    _offset_array[index] = offset;
+  }
+  void set_offset_array(size_t index, HeapWord* high, HeapWord* low) {
+    assert(index < _vs.committed_size(), "index out of range");
+    assert(high >= low, "addresses out of order");
+    assert(pointer_delta(high, low) <= N_words, "offset too large");
+    _offset_array[index] = (u_char)pointer_delta(high, low);
+  }
+  void set_offset_array(HeapWord* left, HeapWord* right, u_char offset) {
+    assert(index_for(right - 1) < _vs.committed_size(),
+           "right address out of range");
+    assert(left  < right, "Heap addresses out of order");
+    size_t num_cards = pointer_delta(right, left) >> LogN_words;
+    memset(&_offset_array[index_for(left)], offset, num_cards);
+  }
+
+  void set_offset_array(size_t left, size_t right, u_char offset) {
+    assert(right < _vs.committed_size(), "right address out of range");
+    assert(left  <= right, "indexes out of order");
+    size_t num_cards = right - left + 1;
+    memset(&_offset_array[left], offset, num_cards);
+  }
+
+  void check_offset_array(size_t index, HeapWord* high, HeapWord* low) const {
+    assert(index < _vs.committed_size(), "index out of range");
+    assert(high >= low, "addresses out of order");
+    assert(pointer_delta(high, low) <= N_words, "offset too large");
+    assert(_offset_array[index] == pointer_delta(high, low),
+           "Wrong offset");
+  }
+
+  bool is_card_boundary(HeapWord* p) const;
+
+  // Return the number of slots needed for an offset array
+  // that covers mem_region_words words.
+  // We always add an extra slot because if an object
+  // ends on a card boundary we put a 0 in the next
+  // offset array slot, so we want that slot always
+  // to be reserved.
+
+  size_t compute_size(size_t mem_region_words) {
+    size_t number_of_slots = (mem_region_words / N_words) + 1;
+    return ReservedSpace::allocation_align_size_up(number_of_slots);
+  }
+
+public:
+  // Initialize the table to cover from "base" to (at least)
+  // "base + init_word_size".  In the future, the table may be expanded
+  // (see "resize" below) up to the size of "_reserved" (which must be at
+  // least "init_word_size".)  The contents of the initial table are
+  // undefined; it is the responsibility of the constituent
+  // BlockOffsetTable(s) to initialize cards.
+  BlockOffsetSharedArray(MemRegion reserved, size_t init_word_size);
+
+  // Notes a change in the committed size of the region covered by the
+  // table.  The "new_word_size" may not be larger than the size of the
+  // reserved region this table covers.
+  void resize(size_t new_word_size);
+
+  void set_bottom(HeapWord* new_bottom);
+
+  // Updates all the BlockOffsetArray's sharing this shared array to
+  // reflect the current "top"'s of their spaces.
+  void update_offset_arrays();   // Not yet implemented!
+
+  // Return the appropriate index into "_offset_array" for "p".
+  size_t index_for(const void* p) const;
+
+  // Return the address indicating the start of the region corresponding to
+  // "index" in "_offset_array".
+  HeapWord* address_for_index(size_t index) const;
+
+  // Shared space support
+  void serialize(SerializeOopClosure* soc, HeapWord* start, HeapWord* end);
+};
+
+//////////////////////////////////////////////////////////////////////////
+// The BlockOffsetArray whose subtypes use the BlockOffsetSharedArray.
+//////////////////////////////////////////////////////////////////////////
+class BlockOffsetArray: public BlockOffsetTable {
+  friend class VMStructs;
+ protected:
+  // The following enums are used by do_block_internal() below
+  enum Action {
+    Action_single,      // BOT records a single block (see single_block())
+    Action_mark,        // BOT marks the start of a block (see mark_block())
+    Action_check        // Check that BOT records block correctly
+                        // (see verify_single_block()).
+  };
+
+  enum SomePrivateConstants {
+    N_words = BlockOffsetSharedArray::N_words,
+    LogN    = BlockOffsetSharedArray::LogN,
+    // entries "e" of at least N_words mean "go back by Base^(e-N_words)."
+    // All entries are less than "N_words + N_powers".
+    LogBase = 4,
+    Base = (1 << LogBase),
+    N_powers = 14
+  };
+
+  static size_t power_to_cards_back(uint i) {
+    return 1 << (LogBase * i);
+  }
+  static size_t power_to_words_back(uint i) {
+    return power_to_cards_back(i) * N_words;
+  }
+  static size_t entry_to_cards_back(u_char entry) {
+    assert(entry >= N_words, "Precondition");
+    return power_to_cards_back(entry - N_words);
+  }
+  static size_t entry_to_words_back(u_char entry) {
+    assert(entry >= N_words, "Precondition");
+    return power_to_words_back(entry - N_words);
+  }
+
+  // The shared array, which is shared with other BlockOffsetArray's
+  // corresponding to different spaces within a generation or span of
+  // memory.
+  BlockOffsetSharedArray* _array;
+
+  // The space that owns this subregion.
+  Space* _sp;
+
+  // If true, array entries are initialized to 0; otherwise, they are
+  // initialized to point backwards to the beginning of the covered region.
+  bool _init_to_zero;
+
+  // Sets the entries
+  // corresponding to the cards starting at "start" and ending at "end"
+  // to point back to the card before "start": the interval [start, end)
+  // is right-open.
+  void set_remainder_to_point_to_start(HeapWord* start, HeapWord* end);
+  // Same as above, except that the args here are a card _index_ interval
+  // that is closed: [start_index, end_index]
+  void set_remainder_to_point_to_start_incl(size_t start, size_t end);
+
+  // A helper function for BOT adjustment/verification work
+  void do_block_internal(HeapWord* blk_start, HeapWord* blk_end, Action action);
+
+ public:
+  // The space may not have its bottom and top set yet, which is why the
+  // region is passed as a parameter.  If "init_to_zero" is true, the
+  // elements of the array are initialized to zero.  Otherwise, they are
+  // initialized to point backwards to the beginning.
+  BlockOffsetArray(BlockOffsetSharedArray* array, MemRegion mr,
+                   bool init_to_zero);
+
+  // Note: this ought to be part of the constructor, but that would require
+  // "this" to be passed as a parameter to a member constructor for
+  // the containing concrete subtype of Space.
+  // This would be legal C++, but MS VC++ doesn't allow it.
+  void set_space(Space* sp) { _sp = sp; }
+
+  // Resets the covered region to the given "mr".
+  void set_region(MemRegion mr) {
+    _bottom = mr.start();
+    _end = mr.end();
+  }
+
+  // Note that the committed size of the covered space may have changed,
+  // so the table size might also wish to change.
+  virtual void resize(size_t new_word_size) {
+    HeapWord* new_end = _bottom + new_word_size;
+    if (_end < new_end && !init_to_zero()) {
+      // verify that the old and new boundaries are also card boundaries
+      assert(_array->is_card_boundary(_end),
+             "_end not a card boundary");
+      assert(_array->is_card_boundary(new_end),
+             "new _end would not be a card boundary");
+      // set all the newly added cards
+      _array->set_offset_array(_end, new_end, N_words);
+    }
+    _end = new_end;  // update _end
+  }
+
+  // Adjust the BOT to show that it has a single block in the
+  // range [blk_start, blk_start + size). All necessary BOT
+  // cards are adjusted, but _unallocated_block isn't.
+  void single_block(HeapWord* blk_start, HeapWord* blk_end);
+  void single_block(HeapWord* blk, size_t size) {
+    single_block(blk, blk + size);
+  }
+
+  // When the alloc_block() call returns, the block offset table should
+  // have enough information such that any subsequent block_start() call
+  // with an argument equal to an address that is within the range
+  // [blk_start, blk_end) would return the value blk_start, provided
+  // there have been no calls in between that reset this information
+  // (e.g. see BlockOffsetArrayNonContigSpace::single_block() call
+  // for an appropriate range covering the said interval).
+  // These methods expect to be called with [blk_start, blk_end)
+  // representing a block of memory in the heap.
+  virtual void alloc_block(HeapWord* blk_start, HeapWord* blk_end);
+  void alloc_block(HeapWord* blk, size_t size) {
+    alloc_block(blk, blk + size);
+  }
+
+  // If true, initialize array slots with no allocated blocks to zero.
+  // Otherwise, make them point back to the front.
+  bool init_to_zero() { return _init_to_zero; }
+
+  // Debugging
+  // Return the index of the last entry in the "active" region.
+  virtual size_t last_active_index() const = 0;
+  // Verify the block offset table
+  void verify() const;
+  void check_all_cards(size_t left_card, size_t right_card) const;
+};
+
+////////////////////////////////////////////////////////////////////////////
+// A subtype of BlockOffsetArray that takes advantage of the fact
+// that its underlying space is a NonContiguousSpace, so that some
+// specialized interfaces can be made available for spaces that
+// manipulate the table.
+////////////////////////////////////////////////////////////////////////////
+class BlockOffsetArrayNonContigSpace: public BlockOffsetArray {
+  friend class VMStructs;
+ private:
+  // The portion [_unallocated_block, _sp.end()) of the space that
+  // is a single block known not to contain any objects.
+  // NOTE: See BlockOffsetArrayUseUnallocatedBlock flag.
+  HeapWord* _unallocated_block;
+
+ public:
+  BlockOffsetArrayNonContigSpace(BlockOffsetSharedArray* array, MemRegion mr):
+    BlockOffsetArray(array, mr, false),
+    _unallocated_block(_bottom) { }
+
+  // accessor
+  HeapWord* unallocated_block() const {
+    assert(BlockOffsetArrayUseUnallocatedBlock,
+           "_unallocated_block is not being maintained");
+    return _unallocated_block;
+  }
+
+  void set_unallocated_block(HeapWord* block) {
+    assert(BlockOffsetArrayUseUnallocatedBlock,
+           "_unallocated_block is not being maintained");
+    assert(block >= _bottom && block <= _end, "out of range");
+    _unallocated_block = block;
+  }
+
+  // These methods expect to be called with [blk_start, blk_end)
+  // representing a block of memory in the heap.
+  void alloc_block(HeapWord* blk_start, HeapWord* blk_end);
+  void alloc_block(HeapWord* blk, size_t size) {
+    alloc_block(blk, blk + size);
+  }
+
+  // The following methods are useful and optimized for a
+  // non-contiguous space.
+
+  // Given a block [blk_start, blk_start + full_blk_size), and
+  // a left_blk_size < full_blk_size, adjust the BOT to show two
+  // blocks [blk_start, blk_start + left_blk_size) and
+  // [blk_start + left_blk_size, blk_start + full_blk_size).
+  // It is assumed (and verified in the non-product VM) that the
+  // BOT was correct for the original block.
+  void split_block(HeapWord* blk_start, size_t full_blk_size,
+                           size_t left_blk_size);
+
+  // Adjust BOT to show that it has a block in the range
+  // [blk_start, blk_start + size). Only the first card
+  // of BOT is touched. It is assumed (and verified in the
+  // non-product VM) that the remaining cards of the block
+  // are correct.
+  void mark_block(HeapWord* blk_start, HeapWord* blk_end);
+  void mark_block(HeapWord* blk, size_t size) {
+    mark_block(blk, blk + size);
+  }
+
+  // Adjust _unallocated_block to indicate that a particular
+  // block has been newly allocated or freed. It is assumed (and
+  // verified in the non-product VM) that the BOT is correct for
+  // the given block.
+  void allocated(HeapWord* blk_start, HeapWord* blk_end) {
+    // Verify that the BOT shows [blk, blk + blk_size) to be one block.
+    verify_single_block(blk_start, blk_end);
+    if (BlockOffsetArrayUseUnallocatedBlock) {
+      _unallocated_block = MAX2(_unallocated_block, blk_end);
+    }
+  }
+
+  void allocated(HeapWord* blk, size_t size) {
+    allocated(blk, blk + size);
+  }
+
+  void freed(HeapWord* blk_start, HeapWord* blk_end);
+  void freed(HeapWord* blk, size_t size) {
+    freed(blk, blk + size);
+  }
+
+  HeapWord* block_start_unsafe(const void* addr) const;
+
+  // Requires "addr" to be the start of a card and returns the
+  // start of the block that contains the given address.
+  HeapWord* block_start_careful(const void* addr) const;
+
+
+  // Verification & debugging: ensure that the offset table reflects
+  // the fact that the block [blk_start, blk_end) or [blk, blk + size)
+  // is a single block of storage. NOTE: can't const this because of
+  // call to non-const do_block_internal() below.
+  void verify_single_block(HeapWord* blk_start, HeapWord* blk_end)
+    PRODUCT_RETURN;
+  void verify_single_block(HeapWord* blk, size_t size) PRODUCT_RETURN;
+
+  // Verify that the given block is before _unallocated_block
+  void verify_not_unallocated(HeapWord* blk_start, HeapWord* blk_end)
+    const PRODUCT_RETURN;
+  void verify_not_unallocated(HeapWord* blk, size_t size)
+    const PRODUCT_RETURN;
+
+  // Debugging support
+  virtual size_t last_active_index() const;
+};
+
+////////////////////////////////////////////////////////////////////////////
+// A subtype of BlockOffsetArray that takes advantage of the fact
+// that its underlying space is a ContiguousSpace, so that its "active"
+// region can be more efficiently tracked (than for a non-contiguous space).
+////////////////////////////////////////////////////////////////////////////
+class BlockOffsetArrayContigSpace: public BlockOffsetArray {
+  friend class VMStructs;
+ private:
+  // allocation boundary at which offset array must be updated
+  HeapWord* _next_offset_threshold;
+  size_t    _next_offset_index;      // index corresponding to that boundary
+
+  // Work function when allocation start crosses threshold.
+  void alloc_block_work(HeapWord* blk_start, HeapWord* blk_end);
+
+ public:
+  BlockOffsetArrayContigSpace(BlockOffsetSharedArray* array, MemRegion mr):
+    BlockOffsetArray(array, mr, true) {
+    _next_offset_threshold = NULL;
+    _next_offset_index = 0;
+  }
+
+  void set_contig_space(ContiguousSpace* sp) { set_space((Space*)sp); }
+
+  // Initialize the threshold for an empty heap.
+  HeapWord* initialize_threshold();
+  // Zero out the entry for _bottom (offset will be zero)
+  void      zero_bottom_entry();
+
+  // Return the next threshold, the point at which the table should be
+  // updated.
+  HeapWord* threshold() const { return _next_offset_threshold; }
+
+  // In general, these methods expect to be called with
+  // [blk_start, blk_end) representing a block of memory in the heap.
+  // In this implementation, however, we are OK even if blk_start and/or
+  // blk_end are NULL because NULL is represented as 0, and thus
+  // never exceeds the "_next_offset_threshold".
+  void alloc_block(HeapWord* blk_start, HeapWord* blk_end) {
+    if (blk_end > _next_offset_threshold) {
+      alloc_block_work(blk_start, blk_end);
+    }
+  }
+  void alloc_block(HeapWord* blk, size_t size) {
+    alloc_block(blk, blk + size);
+  }
+
+  HeapWord* block_start_unsafe(const void* addr) const;
+
+  void serialize(SerializeOopClosure* soc);
+
+  // Debugging support
+  virtual size_t last_active_index() const;
+};