src/hotspot/share/gc/shared/markBitMap.hpp
author rkennke
Wed, 29 Aug 2018 20:15:09 +0200
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child 52577 5b87d3fc1093
permissions -rw-r--r--
8180193: Make marking bitmap code available to other GCs Reviewed-by: shade, stefank
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/*
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 * Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved.
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 *
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 * This code is free software; you can redistribute it and/or modify it
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 * under the terms of the GNU General Public License version 2 only, as
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 * published by the Free Software Foundation.
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 *
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 * This code is distributed in the hope that it will be useful, but WITHOUT
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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 * version 2 for more details (a copy is included in the LICENSE file that
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 * accompanied this code).
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 *
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 * You should have received a copy of the GNU General Public License version
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 * 2 along with this work; if not, write to the Free Software Foundation,
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 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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 *
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 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 * or visit www.oracle.com if you need additional information or have any
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 * questions.
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 *
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 */
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#ifndef SHARE_VM_GC_SHARED_MARKBITMAP_HPP
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#define SHARE_VM_GC_SHARED_MARKBITMAP_HPP
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#include "memory/memRegion.hpp"
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#include "oops/oopsHierarchy.hpp"
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#include "utilities/bitMap.hpp"
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// A generic mark bitmap for concurrent marking.  This is essentially a wrapper
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// around the BitMap class that is based on HeapWords, with one bit per (1 << _shifter) HeapWords.
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class MarkBitMap {
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protected:
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  MemRegion _covered;    // The heap area covered by this bitmap.
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  const int _shifter;    // Shift amount from heap index to bit index in the bitmap.
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  BitMapView _bm;        // The actual bitmap.
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  virtual void check_mark(HeapWord* addr) NOT_DEBUG_RETURN;
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  // Convert from bit offset to address.
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  HeapWord* offset_to_addr(size_t offset) const {
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    return _covered.start() + (offset << _shifter);
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  }
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  // Convert from address to bit offset.
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  size_t addr_to_offset(const HeapWord* addr) const {
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    return pointer_delta(addr, _covered.start()) >> _shifter;
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  }
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public:
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  static size_t compute_size(size_t heap_size);
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  // Returns the amount of bytes on the heap between two marks in the bitmap.
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  static size_t mark_distance();
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  // Returns how many bytes (or bits) of the heap a single byte (or bit) of the
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  // mark bitmap corresponds to. This is the same as the mark distance above.
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  static size_t heap_map_factor() {
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    return mark_distance();
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  }
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  MarkBitMap() : _covered(), _shifter(LogMinObjAlignment), _bm() {}
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  // Initializes the underlying BitMap to cover the given area.
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  void initialize(MemRegion heap, MemRegion storage);
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  // Read marks
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  bool is_marked(oop obj) const;
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  bool is_marked(HeapWord* addr) const {
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    assert(_covered.contains(addr),
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           "Address " PTR_FORMAT " is outside underlying space from " PTR_FORMAT " to " PTR_FORMAT,
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           p2i(addr), p2i(_covered.start()), p2i(_covered.end()));
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    return _bm.at(addr_to_offset(addr));
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  }
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  // Return the address corresponding to the next marked bit at or after
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  // "addr", and before "limit", if "limit" is non-NULL.  If there is no
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  // such bit, returns "limit" if that is non-NULL, or else "endWord()".
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  inline HeapWord* get_next_marked_addr(const HeapWord* addr,
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                                        const HeapWord* limit) const;
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  void print_on_error(outputStream* st, const char* prefix) const;
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  // Write marks.
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  inline void mark(HeapWord* addr);
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  inline void clear(HeapWord* addr);
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  inline void clear(oop obj);
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  inline bool par_mark(HeapWord* addr);
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  inline bool par_mark(oop obj);
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  void clear_range(MemRegion mr);
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};
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#endif // SHARE_VM_GC_SHARED_MARKBITMAP_HPP