1 /*
   2  * Copyright (c) 1997, 2009, 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 // An objArrayOop is an array containing oops.
  26 // Evaluating "String arg[10]" will create an objArrayOop.
  27 
  28 class objArrayOopDesc : public arrayOopDesc {
  29   friend class objArrayKlass;
  30   friend class Runtime1;
  31   friend class psPromotionManager;
  32   friend class CSMarkOopClosure;
  33   friend class G1ParScanPartialArrayClosure;
  34 
  35   template <class T> T* obj_at_addr(int index) const {
  36     assert(is_within_bounds(index), "index out of bounds");
  37     return &((T*)base())[index];
  38   }
  39 
  40 private:
  41   // Give size of objArrayOop in HeapWords minus the header
  42   static int array_size(int length) {
  43     const int OopsPerHeapWord = HeapWordSize/heapOopSize;
  44     assert(OopsPerHeapWord >= 1 && (HeapWordSize % heapOopSize == 0),
  45            "Else the following (new) computation would be in error");
  46 #ifdef ASSERT
  47     // The old code is left in for sanity-checking; it'll
  48     // go away pretty soon. XXX
  49     // Without UseCompressedOops, this is simply:
  50     // oop->length() * HeapWordsPerOop;
  51     // With narrowOops, HeapWordsPerOop is 1/2 or equal 0 as an integer.
  52     // The oop elements are aligned up to wordSize
  53     const int HeapWordsPerOop = heapOopSize/HeapWordSize;
  54     int old_res;
  55     if (HeapWordsPerOop > 0) {
  56       old_res = length * HeapWordsPerOop;
  57     } else {
  58       old_res = align_size_up(length, OopsPerHeapWord)/OopsPerHeapWord;
  59     }
  60 #endif  // ASSERT
  61     int res = ((uint)length + OopsPerHeapWord - 1)/OopsPerHeapWord;
  62     assert(res == old_res, "Inconsistency between old and new.");
  63     return res;
  64   }
  65 
  66  public:
  67   // Returns the offset of the first element.
  68   static int base_offset_in_bytes() {
  69     return arrayOopDesc::base_offset_in_bytes(T_OBJECT);
  70   }
  71 
  72   // base is the address following the header.
  73   HeapWord* base() const      { return (HeapWord*) arrayOopDesc::base(T_OBJECT); }
  74 
  75   // Accessing
  76   oop obj_at(int index) const {
  77     // With UseCompressedOops decode the narrow oop in the objArray to an
  78     // uncompressed oop.  Otherwise this is simply a "*" operator.
  79     if (UseCompressedOops) {
  80       return load_decode_heap_oop(obj_at_addr<narrowOop>(index));
  81     } else {
  82       return load_decode_heap_oop(obj_at_addr<oop>(index));
  83     }
  84   }
  85 
  86   void obj_at_put(int index, oop value) {
  87     if (UseCompressedOops) {
  88       oop_store(obj_at_addr<narrowOop>(index), value);
  89     } else {
  90       oop_store(obj_at_addr<oop>(index), value);
  91     }
  92   }
  93   // Sizing
  94   static int header_size()    { return arrayOopDesc::header_size(T_OBJECT); }
  95   int object_size()           { return object_size(length()); }
  96 
  97   static int object_size(int length) {
  98     // This returns the object size in HeapWords.
  99     uint asz = array_size(length);
 100     uint osz = align_object_size(header_size() + asz);
 101     assert(osz >= asz,   "no overflow");
 102     assert((int)osz > 0, "no overflow");
 103     return (int)osz;
 104   }
 105 
 106   // special iterators for index ranges, returns size of object
 107 #define ObjArrayOop_OOP_ITERATE_DECL(OopClosureType, nv_suffix)     \
 108   int oop_iterate_range(OopClosureType* blk, int start, int end);
 109 
 110   ALL_OOP_OOP_ITERATE_CLOSURES_1(ObjArrayOop_OOP_ITERATE_DECL)
 111   ALL_OOP_OOP_ITERATE_CLOSURES_2(ObjArrayOop_OOP_ITERATE_DECL)
 112 };