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

Java example source code file (freeChunk.hpp)

This example Java source code file (freeChunk.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

error, freechunk, freechunk*, heapword, lp64_only, minchunksize, not_product, null, product_return, share_vm_gc_implementation_concurrentmarksweep_freechunk_hpp, should, usecompressedoops, value_obj_class_spec, vmstructs

The freeChunk.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_CONCURRENTMARKSWEEP_FREECHUNK_HPP
#define SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_FREECHUNK_HPP

#include "memory/allocation.hpp"
#include "memory/memRegion.hpp"
#include "oops/markOop.hpp"
#include "runtime/mutex.hpp"
#include "utilities/debug.hpp"
#include "utilities/globalDefinitions.hpp"
#include "utilities/ostream.hpp"

//
// Free block maintenance for Concurrent Mark Sweep Generation
//
// The main data structure for free blocks are
// . an indexed array of small free blocks, and
// . a dictionary of large free blocks
//

// No virtuals in FreeChunk (don't want any vtables).

// A FreeChunk is merely a chunk that can be in a doubly linked list
// and has a size field. NOTE: FreeChunks are distinguished from allocated
// objects in two ways (by the sweeper), depending on whether the VM is 32 or
// 64 bits.
// In 32 bits or 64 bits without CompressedOops, the second word (prev) has the
// LSB set to indicate a free chunk; allocated objects' klass() pointers
// don't have their LSB set. The corresponding bit in the CMSBitMap is
// set when the chunk is allocated. There are also blocks that "look free"
// but are not part of the free list and should not be coalesced into larger
// free blocks. These free blocks have their two LSB's set.

class FreeChunk VALUE_OBJ_CLASS_SPEC {
  friend class VMStructs;
  // For 64 bit compressed oops, the markOop encodes both the size and the
  // indication that this is a FreeChunk and not an object.
  volatile size_t   _size;
  FreeChunk* _prev;
  FreeChunk* _next;

  markOop mark()     const volatile { return (markOop)_size; }
  void set_mark(markOop m)          { _size = (size_t)m; }

 public:
  NOT_PRODUCT(static const size_t header_size();)

  // Returns "true" if the address indicates that the block represents
  // a free chunk.
  static bool indicatesFreeChunk(const HeapWord* addr) {
    // Force volatile read from addr because value might change between
    // calls.  We really want the read of _mark and _prev from this pointer
    // to be volatile but making the fields volatile causes all sorts of
    // compilation errors.
    return ((volatile FreeChunk*)addr)->is_free();
  }

  bool is_free() const volatile {
    LP64_ONLY(if (UseCompressedOops) return mark()->is_cms_free_chunk(); else)
    return (((intptr_t)_prev) & 0x1) == 0x1;
  }
  bool cantCoalesce() const {
    assert(is_free(), "can't get coalesce bit on not free");
    return (((intptr_t)_prev) & 0x2) == 0x2;
  }
  void dontCoalesce() {
    // the block should be free
    assert(is_free(), "Should look like a free block");
    _prev = (FreeChunk*)(((intptr_t)_prev) | 0x2);
  }
  FreeChunk* prev() const {
    return (FreeChunk*)(((intptr_t)_prev) & ~(0x3));
  }

  debug_only(void* prev_addr() const { return (void*)&_prev; })
  debug_only(void* next_addr() const { return (void*)&_next; })
  debug_only(void* size_addr() const { return (void*)&_size; })

  size_t size() const volatile {
    LP64_ONLY(if (UseCompressedOops) return mark()->get_size(); else )
    return _size;
  }
  void set_size(size_t sz) {
    LP64_ONLY(if (UseCompressedOops) set_mark(markOopDesc::set_size_and_free(sz)); else )
    _size = sz;
  }

  FreeChunk* next()   const { return _next; }

  void link_after(FreeChunk* ptr) {
    link_next(ptr);
    if (ptr != NULL) ptr->link_prev(this);
  }
  void link_next(FreeChunk* ptr) { _next = ptr; }
  void link_prev(FreeChunk* ptr) {
    LP64_ONLY(if (UseCompressedOops) _prev = ptr; else)
    _prev = (FreeChunk*)((intptr_t)ptr | 0x1);
  }
  void clear_next()              { _next = NULL; }
  void markNotFree() {
    // Set _prev (klass) to null before (if) clearing the mark word below
    _prev = NULL;
#ifdef _LP64
    if (UseCompressedOops) {
      OrderAccess::storestore();
      set_mark(markOopDesc::prototype());
    }
#endif
    assert(!is_free(), "Error");
  }

  // Return the address past the end of this chunk
  uintptr_t* end() const { return ((uintptr_t*) this) + size(); }

  // debugging
  void verify()             const PRODUCT_RETURN;
  void verifyList()         const PRODUCT_RETURN;
  void mangleAllocated(size_t size) PRODUCT_RETURN;
  void mangleFreed(size_t size)     PRODUCT_RETURN;

  void print_on(outputStream* st);
};

extern size_t MinChunkSize;


#endif // SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_FREECHUNK_HPP

Other Java examples (source code examples)

Here is a short list of links related to this Java freeChunk.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.