coleenp@622: /*
coleenp@622:  * Copyright 2001-2005 Sun Microsystems, Inc.  All Rights Reserved.
coleenp@622:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
coleenp@622:  *
coleenp@622:  * This code is free software; you can redistribute it and/or modify it
coleenp@622:  * under the terms of the GNU General Public License version 2 only, as
coleenp@622:  * published by the Free Software Foundation.
coleenp@622:  *
coleenp@622:  * This code is distributed in the hope that it will be useful, but WITHOUT
coleenp@622:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
coleenp@622:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
coleenp@622:  * version 2 for more details (a copy is included in the LICENSE file that
coleenp@622:  * accompanied this code).
coleenp@622:  *
coleenp@622:  * You should have received a copy of the GNU General Public License version
coleenp@622:  * 2 along with this work; if not, write to the Free Software Foundation,
coleenp@622:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
coleenp@622:  *
coleenp@622:  * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
coleenp@622:  * CA 95054 USA or visit www.sun.com if you need additional information or
coleenp@622:  * have any questions.
coleenp@622:  *
coleenp@622:  */
coleenp@622: 
coleenp@622: //
coleenp@622: // Free block maintenance for Concurrent Mark Sweep Generation
coleenp@622: //
coleenp@622: // The main data structure for free blocks are
coleenp@622: // . an indexed array of small free blocks, and
coleenp@622: // . a dictionary of large free blocks
coleenp@622: //
coleenp@622: 
coleenp@622: // No virtuals in FreeChunk (don't want any vtables).
coleenp@622: 
coleenp@622: // A FreeChunk is merely a chunk that can be in a doubly linked list
coleenp@622: // and has a size field. NOTE: FreeChunks are distinguished from allocated
coleenp@622: // objects in two ways (by the sweeper), depending on whether the VM is 32 or
coleenp@622: // 64 bits.
coleenp@622: // In 32 bits or 64 bits without CompressedOops, the second word (prev) has the
coleenp@622: // LSB set to indicate a free chunk; allocated objects' klass() pointers
coleenp@622: // don't have their LSB set. The corresponding bit in the CMSBitMap is
coleenp@622: // set when the chunk is allocated. There are also blocks that "look free"
coleenp@622: // but are not part of the free list and should not be coalesced into larger
coleenp@622: // free blocks. These free blocks have their two LSB's set.
coleenp@622: 
coleenp@622: class FreeChunk VALUE_OBJ_CLASS_SPEC {
coleenp@622:   friend class VMStructs;
coleenp@622:   // For 64 bit compressed oops, the markOop encodes both the size and the
coleenp@622:   // indication that this is a FreeChunk and not an object.
coleenp@622:   volatile size_t   _size;
coleenp@622:   FreeChunk* _prev;
coleenp@622:   FreeChunk* _next;
coleenp@622: 
coleenp@622:   markOop mark()     const volatile { return (markOop)_size; }
coleenp@622:   void set_mark(markOop m)          { _size = (size_t)m; }
coleenp@622: 
coleenp@622:  public:
coleenp@622:   NOT_PRODUCT(static const size_t header_size();)
coleenp@622: 
coleenp@622:   // Returns "true" if the address indicates that the block represents
coleenp@622:   // a free chunk.
coleenp@622:   static bool indicatesFreeChunk(const HeapWord* addr) {
coleenp@622:     // Force volatile read from addr because value might change between
coleenp@622:     // calls.  We really want the read of _mark and _prev from this pointer
coleenp@622:     // to be volatile but making the fields volatile causes all sorts of
coleenp@622:     // compilation errors.
coleenp@622:     return ((volatile FreeChunk*)addr)->isFree();
coleenp@622:   }
coleenp@622: 
coleenp@622:   bool isFree() const volatile {
coleenp@622:     LP64_ONLY(if (UseCompressedOops) return mark()->is_cms_free_chunk(); else)
coleenp@622:     return (((intptr_t)_prev) & 0x1) == 0x1;
coleenp@622:   }
coleenp@622:   bool cantCoalesce() const {
coleenp@622:     assert(isFree(), "can't get coalesce bit on not free");
coleenp@622:     return (((intptr_t)_prev) & 0x2) == 0x2;
coleenp@622:   }
coleenp@622:   void dontCoalesce() {
coleenp@622:     // the block should be free
coleenp@622:     assert(isFree(), "Should look like a free block");
coleenp@622:     _prev = (FreeChunk*)(((intptr_t)_prev) | 0x2);
coleenp@622:   }
coleenp@622:   FreeChunk* prev() const {
coleenp@622:     return (FreeChunk*)(((intptr_t)_prev) & ~(0x3));
coleenp@622:   }
coleenp@622: 
coleenp@622:   debug_only(void* prev_addr() const { return (void*)&_prev; })
coleenp@622: 
coleenp@622:   size_t size() const volatile {
coleenp@622:     LP64_ONLY(if (UseCompressedOops) return mark()->get_size(); else )
coleenp@622:     return _size;
coleenp@622:   }
coleenp@622:   void setSize(size_t sz) {
coleenp@622:     LP64_ONLY(if (UseCompressedOops) set_mark(markOopDesc::set_size_and_free(sz)); else )
coleenp@622:     _size = sz;
coleenp@622:   }
coleenp@622: 
coleenp@622:   FreeChunk* next()   const { return _next; }
coleenp@622: 
coleenp@622:   void linkAfter(FreeChunk* ptr) {
coleenp@622:     linkNext(ptr);
coleenp@622:     if (ptr != NULL) ptr->linkPrev(this);
coleenp@622:   }
coleenp@622:   void linkAfterNonNull(FreeChunk* ptr) {
coleenp@622:     assert(ptr != NULL, "precondition violation");
coleenp@622:     linkNext(ptr);
coleenp@622:     ptr->linkPrev(this);
coleenp@622:   }
coleenp@622:   void linkNext(FreeChunk* ptr) { _next = ptr; }
coleenp@622:   void linkPrev(FreeChunk* ptr) {
coleenp@622:      LP64_ONLY(if (UseCompressedOops) _prev = ptr; else)
coleenp@622:      _prev = (FreeChunk*)((intptr_t)ptr | 0x1);
coleenp@622:   }
coleenp@622:   void clearPrev()              { _prev = NULL; }
coleenp@622:   void clearNext()              { _next = NULL; }
coleenp@622:   void markNotFree() {
coleenp@622:    LP64_ONLY(if (UseCompressedOops) set_mark(markOopDesc::prototype());)
coleenp@622:    // Also set _prev to null
coleenp@622:    _prev = NULL;
coleenp@622:   }
coleenp@622: 
coleenp@622:   // Return the address past the end of this chunk
coleenp@622:   HeapWord* end() const { return ((HeapWord*) this) + size(); }
coleenp@622: 
coleenp@622:   // debugging
coleenp@622:   void verify()             const PRODUCT_RETURN;
coleenp@622:   void verifyList()         const PRODUCT_RETURN;
coleenp@622:   void mangleAllocated(size_t size) PRODUCT_RETURN;
coleenp@622:   void mangleFreed(size_t size)     PRODUCT_RETURN;
coleenp@622: };
coleenp@622: 
coleenp@622: // Alignment helpers etc.
coleenp@622: #define numQuanta(x,y) ((x+y-1)/y)
coleenp@622: enum AlignmentConstants {
coleenp@622:   MinChunkSize = numQuanta(sizeof(FreeChunk), MinObjAlignmentInBytes) * MinObjAlignment
coleenp@622: };
coleenp@622: