1 /*
   2  * Copyright (c) 1997, 2012, 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 #ifndef SHARE_VM_OOPS_OBJARRAYOOP_HPP
  26 #define SHARE_VM_OOPS_OBJARRAYOOP_HPP
  27 
  28 #include "oops/arrayOop.hpp"
  29 
  30 // An objArrayOop is an array containing oops.
  31 // Evaluating "String arg[10]" will create an objArrayOop.
  32 
  33 class objArrayOopDesc : public arrayOopDesc {
  34   friend class ObjArrayKlass;
  35   friend class Runtime1;
  36   friend class psPromotionManager;
  37   friend class CSetMarkOopClosure;
  38   friend class G1ParScanPartialArrayClosure;
  39 
  40   template <class T> T* obj_at_addr(int index) const {
  41     assert(is_within_bounds(index), "index out of bounds");
  42     return &((T*)base())[index];
  43   }
  44 
  45 private:
  46   // Give size of objArrayOop in HeapWords minus the header
  47   static int array_size(int length) {
  48     const uint OopsPerHeapWord = HeapWordSize/heapOopSize;
  49     assert(OopsPerHeapWord >= 1 && (HeapWordSize % heapOopSize == 0),
  50            "Else the following (new) computation would be in error");
  51     uint res = ((uint)length + OopsPerHeapWord - 1)/OopsPerHeapWord;
  52 #ifdef ASSERT
  53     // The old code is left in for sanity-checking; it'll
  54     // go away pretty soon. XXX
  55     // Without UseCompressedOops, this is simply:
  56     // oop->length() * HeapWordsPerOop;
  57     // With narrowOops, HeapWordsPerOop is 1/2 or equal 0 as an integer.
  58     // The oop elements are aligned up to wordSize
  59     const uint HeapWordsPerOop = heapOopSize/HeapWordSize;
  60     uint old_res;
  61     if (HeapWordsPerOop > 0) {
  62       old_res = length * HeapWordsPerOop;
  63     } else {
  64       old_res = align_size_up((uint)length, OopsPerHeapWord)/OopsPerHeapWord;
  65     }
  66     assert(res == old_res, "Inconsistency between old and new.");
  67 #endif  // ASSERT
  68     return res;
  69   }
  70 
  71  public:
  72   // Returns the offset of the first element.
  73   static int base_offset_in_bytes() {
  74     return arrayOopDesc::base_offset_in_bytes(T_OBJECT);
  75   }
  76 
  77   // base is the address following the header.
  78   HeapWord* base() const      { return (HeapWord*) arrayOopDesc::base(T_OBJECT); }
  79 
  80   // Accessing
  81   oop obj_at(int index) const {
  82     // With UseCompressedOops decode the narrow oop in the objArray to an
  83     // uncompressed oop.  Otherwise this is simply a "*" operator.
  84     if (UseCompressedOops) {
  85       return load_decode_heap_oop(obj_at_addr<narrowOop>(index));
  86     } else {
  87       return load_decode_heap_oop(obj_at_addr<oop>(index));
  88     }
  89   }
  90 
  91   void obj_at_put(int index, oop value) {
  92     if (UseCompressedOops) {
  93       oop_store(obj_at_addr<narrowOop>(index), value);
  94     } else {
  95       oop_store(obj_at_addr<oop>(index), value);
  96     }
  97   }
  98   // Sizing
  99   static int header_size()    { return arrayOopDesc::header_size(T_OBJECT); }
 100   int object_size()           { return object_size(length()); }
 101 
 102   static int object_size(int length) {
 103     // This returns the object size in HeapWords.
 104     uint asz = array_size(length);
 105     uint osz = align_object_size(header_size() + asz);
 106     assert(osz >= asz,   "no overflow");
 107     assert((int)osz > 0, "no overflow");
 108     return (int)osz;
 109   }
 110 
 111   // special iterators for index ranges, returns size of object
 112 #define ObjArrayOop_OOP_ITERATE_DECL(OopClosureType, nv_suffix)     \
 113   int oop_iterate_range(OopClosureType* blk, int start, int end);
 114 
 115   ALL_OOP_OOP_ITERATE_CLOSURES_1(ObjArrayOop_OOP_ITERATE_DECL)
 116   ALL_OOP_OOP_ITERATE_CLOSURES_2(ObjArrayOop_OOP_ITERATE_DECL)
 117 };
 118 
 119 #endif // SHARE_VM_OOPS_OBJARRAYOOP_HPP