jdk8-mips64-public/hotspot: src/share/vm/gc_implementation/concurrentMarkSweep/freeChunk.hpp@790e66e5fbac (annotated)

src/share/vm/gc_implementation/concurrentMarkSweep/freeChunk.hpp@790e66e5fbac (annotated)

src/share/vm/gc_implementation/concurrentMarkSweep/freeChunk.hpp

Mon, 09 Jun 2008 11:51:19 -0400

author: coleenp
date: Mon, 09 Jun 2008 11:51:19 -0400
changeset 622: 790e66e5fbac
child 631: d1605aabd0a1
child 698: 12eea04c8b06
permissions: -rw-r--r--

6687581: Make CMS work with compressed oops
Summary: Make FreeChunk read markword instead of LSB in _klass pointer to indicate that it's a FreeChunk for compressed oops.
Reviewed-by: ysr, jmasa

 /*
  * Copyright 2001-2005 Sun Microsystems, Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
  * CA 95054 USA or visit www.sun.com if you need additional information or
  * have any questions.
  *
  */
 //
 // 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)->isFree();
   }
   bool isFree() const volatile {
     LP64_ONLY(if (UseCompressedOops) return mark()->is_cms_free_chunk(); else)
     return (((intptr_t)_prev) & 0x1) == 0x1;
   }
   bool cantCoalesce() const {
     assert(isFree(), "can't get coalesce bit on not free");
     return (((intptr_t)_prev) & 0x2) == 0x2;
   }
   void dontCoalesce() {
     // the block should be free
     assert(isFree(), "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; })
   size_t size() const volatile {
     LP64_ONLY(if (UseCompressedOops) return mark()->get_size(); else )
     return _size;
   }
   void setSize(size_t sz) {
     LP64_ONLY(if (UseCompressedOops) set_mark(markOopDesc::set_size_and_free(sz)); else )
     _size = sz;
   }
   FreeChunk* next()   const { return _next; }
   void linkAfter(FreeChunk* ptr) {
     linkNext(ptr);
     if (ptr != NULL) ptr->linkPrev(this);
   }
   void linkAfterNonNull(FreeChunk* ptr) {
     assert(ptr != NULL, "precondition violation");
     linkNext(ptr);
     ptr->linkPrev(this);
   }
   void linkNext(FreeChunk* ptr) { _next = ptr; }
   void linkPrev(FreeChunk* ptr) {
      LP64_ONLY(if (UseCompressedOops) _prev = ptr; else)
      _prev = (FreeChunk*)((intptr_t)ptr | 0x1);
   }
   void clearPrev()              { _prev = NULL; }
   void clearNext()              { _next = NULL; }
   void markNotFree() {
    LP64_ONLY(if (UseCompressedOops) set_mark(markOopDesc::prototype());)
    // Also set _prev to null
    _prev = NULL;
   }
   // Return the address past the end of this chunk
   HeapWord* end() const { return ((HeapWord*) 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;
 };
 // Alignment helpers etc.
 #define numQuanta(x,y) ((x+y-1)/y)
 enum AlignmentConstants {
   MinChunkSize = numQuanta(sizeof(FreeChunk), MinObjAlignmentInBytes) * MinObjAlignment
 };

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src/share/vm/gc_implementation/concurrentMarkSweep/freeChunk.hpp@790e66e5fbac (annotated)

src/share/vm/gc_implementation/concurrentMarkSweep/freeChunk.hpp