/*

 * 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.

 *

 */

//

// This class can be used to locate the beginning of an object in the

// covered region.

//

class ObjectStartArray : public CHeapObj {

 friend class VerifyObjectStartArrayClosure;

 private:

  PSVirtualSpace  _virtual_space;

  MemRegion       _reserved_region;

  MemRegion       _covered_region;

  MemRegion       _blocks_region;

  jbyte*          _raw_base;

  jbyte*          _offset_base;

 public:

  enum BlockValueConstants {

    clean_block                  = -1

  };

  enum BlockSizeConstants {

    block_shift                  = 9,

    block_size                   = 1 << block_shift,

    block_size_in_words          = block_size / sizeof(HeapWord)

  };

 protected:

  // Mapping from address to object start array entry

  jbyte* block_for_addr(void* p) const {

    assert(_covered_region.contains(p),

           "out of bounds access to object start array");

    jbyte* result = &_offset_base[uintptr_t(p) >> block_shift];

    assert(_blocks_region.contains(result),

           "out of bounds result in byte_for");

    return result;

  }

  // Mapping from object start array entry to address of first word

  HeapWord* addr_for_block(jbyte* p) {

    assert(_blocks_region.contains(p),

           "out of bounds access to object start array");

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

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

    assert(_covered_region.contains(result),

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

    return result;

  }

  // Mapping that includes the derived offset.

  // If the block is clean, returns the last address in the covered region.

  // If the block is < index 0, returns the start of the covered region.

  HeapWord* offset_addr_for_block (jbyte* p) const {

    // We have to do this before the assert

    if (p < _raw_base) {

      return _covered_region.start();

    }

    assert(_blocks_region.contains(p),

           "out of bounds access to object start array");

    if (*p == clean_block) {

      return _covered_region.end();

    }

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

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

    result += *p;

    assert(_covered_region.contains(result),

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

    return result;

  }

 public:

  // This method is in lieu of a constructor, so that this class can be

  // embedded inline in other classes.

  void initialize(MemRegion reserved_region);

  void set_covered_region(MemRegion mr);

  void reset();

  MemRegion covered_region() { return _covered_region; }

  void allocate_block(HeapWord* p) {

    assert(_covered_region.contains(p), "Must be in covered region");

    jbyte* block = block_for_addr(p);

    HeapWord* block_base = addr_for_block(block);

    size_t offset = pointer_delta(p, block_base, sizeof(HeapWord*));

    assert(offset < 128, "Sanity");

    // When doing MT offsets, we can't assert this.

    //assert(offset > *block, "Found backwards allocation");

    *block = (jbyte)offset;

    // tty->print_cr("[%p]", p);

  }

  // Optimized for finding the first object that crosses into

  // a given block. The blocks contain the offset of the last

  // object in that block. Scroll backwards by one, and the first

  // object hit should be at the beginning of the block

  HeapWord* object_start(HeapWord* addr) const {

    assert(_covered_region.contains(addr), "Must be in covered region");

    jbyte* block = block_for_addr(addr);

    HeapWord* scroll_forward = offset_addr_for_block(block--);

    while (scroll_forward > addr) {

      scroll_forward = offset_addr_for_block(block--);

    }

    HeapWord* next = scroll_forward;

    while (next <= addr) {

      scroll_forward = next;

      next += oop(next)->size();

    }

    assert(scroll_forward <= addr, "wrong order for current and arg");

    assert(addr <= next, "wrong order for arg and next");

    return scroll_forward;

  }

  bool is_block_allocated(HeapWord* addr) {

    assert(_covered_region.contains(addr), "Must be in covered region");

    jbyte* block = block_for_addr(addr);

    if (*block == clean_block)

      return false;

    return true;

  }

  // Return true if an object starts in the range of heap addresses.

  // If an object starts at an address corresponding to

  // "start", the method will return true.

  bool object_starts_in_range(HeapWord* start_addr, HeapWord* end_addr) const;

};