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 /*

  * Copyright (c) 2001, 2010, 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

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 #ifndef SHARE_VM_GC_IMPLEMENTATION_PARALLELSCAVENGE_OBJECTSTARTARRAY_HPP

 #define SHARE_VM_GC_IMPLEMENTATION_PARALLELSCAVENGE_OBJECTSTARTARRAY_HPP

 #include "gc_implementation/parallelScavenge/psVirtualspace.hpp"

 #include "memory/allocation.hpp"

 #include "memory/memRegion.hpp"

 #include "oops/oop.hpp"

 //

 // 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;

 };

 #endif // SHARE_VM_GC_IMPLEMENTATION_PARALLELSCAVENGE_OBJECTSTARTARRAY_HPP