1 /*
   2  * Copyright (c) 2001, 2014, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
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   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
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  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
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  24 
  25 #ifndef SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_FREECHUNK_HPP
  26 #define SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_FREECHUNK_HPP
  27 
  28 #include "memory/allocation.hpp"
  29 #include "memory/memRegion.hpp"
  30 #include "oops/markOop.hpp"
  31 #include "runtime/mutex.hpp"
  32 #include "runtime/orderAccess.hpp"
  33 #include "utilities/debug.hpp"
  34 #include "utilities/globalDefinitions.hpp"
  35 #include "utilities/ostream.hpp"
  36 
  37 //
  38 // Free block maintenance for Concurrent Mark Sweep Generation
  39 //
  40 // The main data structure for free blocks are
  41 // . an indexed array of small free blocks, and
  42 // . a dictionary of large free blocks
  43 //
  44 
  45 // No virtuals in FreeChunk (don't want any vtables).
  46 
  47 // A FreeChunk is merely a chunk that can be in a doubly linked list
  48 // and has a size field. NOTE: FreeChunks are distinguished from allocated
  49 // objects in two ways (by the sweeper), depending on whether the VM is 32 or
  50 // 64 bits.
  51 // In 32 bits or 64 bits without CompressedOops, the second word (prev) has the
  52 // LSB set to indicate a free chunk; allocated objects' klass() pointers
  53 // don't have their LSB set. The corresponding bit in the CMSBitMap is
  54 // set when the chunk is allocated. There are also blocks that "look free"
  55 // but are not part of the free list and should not be coalesced into larger
  56 // free blocks. These free blocks have their two LSB's set.
  57 
  58 class FreeChunk VALUE_OBJ_CLASS_SPEC {
  59   friend class VMStructs;
  60   // For 64 bit compressed oops, the markOop encodes both the size and the
  61   // indication that this is a FreeChunk and not an object.
  62   volatile size_t   _size;
  63   FreeChunk* _prev;
  64   FreeChunk* _next;
  65 
  66   markOop mark()     const volatile { return (markOop)_size; }
  67   void set_mark(markOop m)          { _size = (size_t)m; }
  68 
  69  public:
  70   NOT_PRODUCT(static const size_t header_size();)
  71 
  72   // Returns "true" if the address indicates that the block represents
  73   // a free chunk.
  74   static bool indicatesFreeChunk(const HeapWord* addr) {
  75     // Force volatile read from addr because value might change between
  76     // calls.  We really want the read of _mark and _prev from this pointer
  77     // to be volatile but making the fields volatile causes all sorts of
  78     // compilation errors.
  79     return ((volatile FreeChunk*)addr)->is_free();
  80   }
  81 
  82   bool is_free() const volatile {
  83     LP64_ONLY(if (UseCompressedOops) return mark()->is_cms_free_chunk(); else)
  84     return (((intptr_t)_prev) & 0x1) == 0x1;
  85   }
  86   bool cantCoalesce() const {
  87     assert(is_free(), "can't get coalesce bit on not free");
  88     return (((intptr_t)_prev) & 0x2) == 0x2;
  89   }
  90   void dontCoalesce() {
  91     // the block should be free
  92     assert(is_free(), "Should look like a free block");
  93     _prev = (FreeChunk*)(((intptr_t)_prev) | 0x2);
  94   }
  95   FreeChunk* prev() const {
  96     return (FreeChunk*)(((intptr_t)_prev) & ~(0x3));
  97   }
  98 
  99   debug_only(void* prev_addr() const { return (void*)&_prev; })
 100   debug_only(void* next_addr() const { return (void*)&_next; })
 101   debug_only(void* size_addr() const { return (void*)&_size; })
 102 
 103   size_t size() const volatile {
 104     LP64_ONLY(if (UseCompressedOops) return mark()->get_size(); else )
 105     return _size;
 106   }
 107   void set_size(size_t sz) {
 108     LP64_ONLY(if (UseCompressedOops) set_mark(markOopDesc::set_size_and_free(sz)); else )
 109     _size = sz;
 110   }
 111 
 112   FreeChunk* next()   const { return _next; }
 113 
 114   void link_after(FreeChunk* ptr) {
 115     link_next(ptr);
 116     if (ptr != NULL) ptr->link_prev(this);
 117   }
 118   void link_next(FreeChunk* ptr) { _next = ptr; }
 119   void link_prev(FreeChunk* ptr) {
 120     LP64_ONLY(if (UseCompressedOops) _prev = ptr; else)
 121     _prev = (FreeChunk*)((intptr_t)ptr | 0x1);
 122   }
 123   void clear_next()              { _next = NULL; }
 124   void markNotFree() {
 125     // Set _prev (klass) to null before (if) clearing the mark word below
 126     _prev = NULL;
 127 #ifdef _LP64
 128     if (UseCompressedOops) {
 129       OrderAccess::storestore();
 130       set_mark(markOopDesc::prototype());
 131     }
 132 #endif
 133     assert(!is_free(), "Error");
 134   }
 135 
 136   // Return the address past the end of this chunk
 137   uintptr_t* end() const { return ((uintptr_t*) this) + size(); }
 138 
 139   // debugging
 140   void verify()             const PRODUCT_RETURN;
 141   void verifyList()         const PRODUCT_RETURN;
 142   void mangleAllocated(size_t size) PRODUCT_RETURN;
 143   void mangleFreed(size_t size)     PRODUCT_RETURN;
 144 
 145   void print_on(outputStream* st);
 146 };
 147 
 148 extern size_t MinChunkSize;
 149 
 150 
 151 #endif // SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_FREECHUNK_HPP