alvinalexander.com | career | drupal | java | mac | mysql | perl | scala | uml | unix  

Java example source code file (objectStartArray.hpp)

This example Java source code file (objectStartArray.hpp) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

blocksizeconstants, blockvalueconstants, cheapobj, heapword, memregion, must, psvirtualspace, sanity, share_vm_gc_implementation_parallelscavenge_objectstartarray_hpp, verifyobjectstartarrayclosure

The objectStartArray.hpp Java example source code

/*
 * Copyright (c) 2001, 2012, 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
 * questions.
 *
 */

#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<mtGC> {
 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

Other Java examples (source code examples)

Here is a short list of links related to this Java objectStartArray.hpp source code file:

... this post is sponsored by my books ...

#1 New Release!

FP Best Seller

 

new blog posts

 

Copyright 1998-2021 Alvin Alexander, alvinalexander.com
All Rights Reserved.

A percentage of advertising revenue from
pages under the /java/jwarehouse URI on this website is
paid back to open source projects.