1 /*
   2  * Copyright (c) 2002, 2008, 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.
   8  *
   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
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  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
  21  * questions.
  22  *
  23  */
  24 
  25 //
  26 // PSPromotionLAB is a parallel scavenge promotion lab. This class acts very
  27 // much like a MutableSpace. We couldn't embed a MutableSpace, though, as
  28 // it has a considerable number of asserts and invariants that are violated.
  29 //
  30 
  31 class ObjectStartArray;
  32 
  33 class PSPromotionLAB : public CHeapObj {
  34  protected:
  35   static size_t filler_header_size;
  36 
  37   enum LabState {
  38     needs_flush,
  39     flushed,
  40     zero_size
  41   };
  42 
  43   HeapWord* _top;
  44   HeapWord* _bottom;
  45   HeapWord* _end;
  46   LabState _state;
  47 
  48   void set_top(HeapWord* value)    { _top = value; }
  49   void set_bottom(HeapWord* value) { _bottom = value; }
  50   void set_end(HeapWord* value)    { _end = value; }
  51 
  52   // The shared initialize code invokes this.
  53   debug_only(virtual bool lab_is_valid(MemRegion lab) { return false; });
  54 
  55   PSPromotionLAB() : _top(NULL), _bottom(NULL), _end(NULL) { }
  56 
  57  public:
  58   // Filling and flushing.
  59   void initialize(MemRegion lab);
  60 
  61   virtual void flush();
  62 
  63   // Accessors
  64   HeapWord* bottom() const           { return _bottom; }
  65   HeapWord* end() const              { return _end;    }
  66   HeapWord* top() const              { return _top;    }
  67 
  68   bool is_flushed()                  { return _state == flushed; }
  69 
  70   bool unallocate_object(oop obj);
  71 
  72   // Returns a subregion containing all objects in this space.
  73   MemRegion used_region()            { return MemRegion(bottom(), top()); }
  74 
  75   // Boolean querries.
  76   bool is_empty() const              { return used() == 0; }
  77   bool not_empty() const             { return used() > 0; }
  78   bool contains(const void* p) const { return _bottom <= p && p < _end; }
  79 
  80   // Size computations.  Sizes are in bytes.
  81   size_t capacity() const            { return byte_size(bottom(), end()); }
  82   size_t used() const                { return byte_size(bottom(), top()); }
  83   size_t free() const                { return byte_size(top(),    end()); }
  84 };
  85 
  86 class PSYoungPromotionLAB : public PSPromotionLAB {
  87  public:
  88   PSYoungPromotionLAB() { }
  89 
  90   // Not MT safe
  91   HeapWord* allocate(size_t size) {
  92     // Can't assert this, when young fills, we keep the LAB around, but flushed.
  93     // assert(_state != flushed, "Sanity");
  94     HeapWord* obj = top();
  95     HeapWord* new_top = obj + size;
  96     // The 'new_top>obj' check is needed to detect overflow of obj+size.
  97     if (new_top > obj && new_top <= end()) {
  98       set_top(new_top);
  99       assert(is_object_aligned((intptr_t)obj) && is_object_aligned((intptr_t)new_top),
 100              "checking alignment");
 101       return obj;
 102     }
 103 
 104     return NULL;
 105   }
 106 
 107   debug_only(virtual bool lab_is_valid(MemRegion lab));
 108 };
 109 
 110 class PSOldPromotionLAB : public PSPromotionLAB {
 111  private:
 112   ObjectStartArray* _start_array;
 113 
 114  public:
 115   PSOldPromotionLAB() : _start_array(NULL) { }
 116   PSOldPromotionLAB(ObjectStartArray* start_array) : _start_array(start_array) { }
 117 
 118   void set_start_array(ObjectStartArray* start_array) { _start_array = start_array; }
 119 
 120   void flush();
 121 
 122   // Not MT safe
 123   HeapWord* allocate(size_t size) {
 124     // Cannot test for this now that we're doing promotion failures
 125     // assert(_state != flushed, "Sanity");
 126     assert(_start_array != NULL, "Sanity");
 127     HeapWord* obj = top();
 128     HeapWord* new_top = obj + size;
 129     // The 'new_top>obj' check is needed to detect overflow of obj+size.
 130     if (new_top > obj && new_top <= end()) {
 131       set_top(new_top);
 132       assert(is_object_aligned((intptr_t)obj) && is_object_aligned((intptr_t)new_top),
 133              "checking alignment");
 134       _start_array->allocate_block(obj);
 135       return obj;
 136     }
 137 
 138     return NULL;
 139   }
 140 
 141   debug_only(virtual bool lab_is_valid(MemRegion lab));
 142 };