1 /*
   2  * Copyright (c) 1997, 2019, 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
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  23  */
  24 
  25 #ifndef SHARE_OOPS_OBJARRAYOOP_HPP
  26 #define SHARE_OOPS_OBJARRAYOOP_HPP
  27 
  28 #include "oops/arrayOop.hpp"
  29 #include "utilities/align.hpp"
  30 
  31 class Klass;
  32 
  33 // An objArrayOop is an array containing oops.
  34 // Evaluating "String arg[10]" will create an objArrayOop.
  35 
  36 class objArrayOopDesc : public arrayOopDesc {
  37   friend class ObjArrayKlass;
  38   friend class Runtime1;
  39   friend class psPromotionManager;
  40   friend class CSetMarkOopClosure;
  41   friend class G1ParScanPartialArrayClosure;
  42 
  43   template <class T> T* obj_at_addr(int index) const;
  44   template <class T> T* obj_at_addr_raw(int index) const;
  45 
  46   template <class T>
  47   static ptrdiff_t obj_at_offset(int index) {
  48     return base_offset_in_bytes() + sizeof(T) * index;
  49   }
  50 
  51 private:
  52   // Give size of objArrayOop in HeapWords minus the header
  53   static int array_size(int length) {
  54     const uint OopsPerHeapWord = HeapWordSize/heapOopSize;
  55     assert(OopsPerHeapWord >= 1 && (HeapWordSize % heapOopSize == 0),
  56            "Else the following (new) computation would be in error");
  57     uint res = ((uint)length + OopsPerHeapWord - 1)/OopsPerHeapWord;
  58 #ifdef ASSERT
  59     // The old code is left in for sanity-checking; it'll
  60     // go away pretty soon. XXX
  61     // Without UseCompressedOops, this is simply:
  62     // oop->length() * HeapWordsPerOop;
  63     // With narrowOops, HeapWordsPerOop is 1/2 or equal 0 as an integer.
  64     // The oop elements are aligned up to wordSize
  65     const uint HeapWordsPerOop = heapOopSize/HeapWordSize;
  66     uint old_res;
  67     if (HeapWordsPerOop > 0) {
  68       old_res = length * HeapWordsPerOop;
  69     } else {
  70       old_res = align_up((uint)length, OopsPerHeapWord)/OopsPerHeapWord;
  71     }
  72     assert(res == old_res, "Inconsistency between old and new.");
  73 #endif  // ASSERT
  74     return res;
  75   }
  76 
  77  public:
  78   // Returns the offset of the first element.
  79   static int base_offset_in_bytes() {
  80     return arrayOopDesc::base_offset_in_bytes(T_OBJECT);
  81   }
  82 
  83   // base is the address following the header.
  84   HeapWord* base() const;
  85   HeapWord* base_raw() const;
  86 
  87   // Accessing
  88   oop obj_at(int index) const;
  89 
  90   void obj_at_put(int index, oop value);
  91 
  92   oop atomic_compare_exchange_oop(int index, oop exchange_value, oop compare_value);
  93 
  94   // Sizing
  95   static int header_size()    { return arrayOopDesc::header_size(T_OBJECT); }
  96   int object_size()           { return object_size(length()); }
  97 
  98   static int object_size(int length) {
  99     // This returns the object size in HeapWords.
 100     uint asz = array_size(length);
 101     uint osz = align_object_size(header_size() + asz);
 102     assert(osz >= asz,   "no overflow");
 103     assert((int)osz > 0, "no overflow");
 104     return (int)osz;
 105   }
 106 
 107   Klass* element_klass();
 108 
 109 public:
 110   // special iterators for index ranges, returns size of object
 111   template <typename OopClosureType>
 112   void oop_iterate_range(OopClosureType* blk, int start, int end);
 113 };
 114 
 115 #endif // SHARE_OOPS_OBJARRAYOOP_HPP