1 /*
  2  * Copyright (c) 1997, 2022, 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.
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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 #include <type_traits>
 31 
 32 class Klass;
 33 
 34 // An objArrayOop is an array containing oops.
 35 // Evaluating "String arg[10]" will create an objArrayOop.
 36 
 37 class objArrayOopDesc : public arrayOopDesc {
 38   friend class ObjArrayKlass;
 39   friend class Runtime1;
 40   friend class psPromotionManager;
 41   friend class CSetMarkWordClosure;
 42   friend class Continuation;
 43   template <typename T>
 44   friend class RawOopWriter;
 45 
 46   template <class T> T* obj_at_addr(int index) const;
 47 
 48   template <class T>
 49   static ptrdiff_t obj_at_offset(int index) {
 50     return base_offset_in_bytes() + sizeof(T) * index;
 51   }
 52 
 53 private:
 54   // Give size of objArrayOop in HeapWords minus the header
 55   static int array_size(int length) {
 56     const uint OopsPerHeapWord = HeapWordSize/heapOopSize;
 57     assert(OopsPerHeapWord >= 1 && (HeapWordSize % heapOopSize == 0),
 58            "Else the following (new) computation would be in error");
 59     uint res = ((uint)length + OopsPerHeapWord - 1)/OopsPerHeapWord;
 60 #ifdef ASSERT
 61     // The old code is left in for sanity-checking; it'll
 62     // go away pretty soon. XXX
 63     // Without UseCompressedOops, this is simply:
 64     // oop->length() * HeapWordsPerOop;
 65     // With narrowOops, HeapWordsPerOop is 1/2 or equal 0 as an integer.
 66     // The oop elements are aligned up to wordSize
 67     const uint HeapWordsPerOop = heapOopSize/HeapWordSize;
 68     uint old_res;
 69     if (HeapWordsPerOop > 0) {
 70       old_res = length * HeapWordsPerOop;
 71     } else {
 72       old_res = align_up((uint)length, OopsPerHeapWord)/OopsPerHeapWord;
 73     }
 74     assert(res == old_res, "Inconsistency between old and new.");
 75 #endif  // ASSERT
 76     return res;
 77   }
 78 
 79  public:
 80   // Returns the offset of the first element.
 81   static int base_offset_in_bytes() {
 82     return arrayOopDesc::base_offset_in_bytes(T_OBJECT);
 83   }
 84 
 85   // base is the address following the header.
 86   HeapWord* base() const;
 87 
 88   // Accessing
 89   oop obj_at(int index) const;
 90 
 91   void obj_at_put(int index, oop value);
 92 
 93   oop atomic_compare_exchange_oop(int index, oop exchange_value, oop compare_value);
 94 
 95   // Sizing
 96   static int header_size()    { return arrayOopDesc::header_size(T_OBJECT); }
 97   size_t object_size()        { return object_size(length()); }
 98 
 99   static size_t object_size(int length) {
100     // This returns the object size in HeapWords.
101     uint asz = array_size(length);
102     uint osz = align_object_size(header_size() + asz);
103     assert(osz >= asz,   "no overflow");
104     assert((int)osz > 0, "no overflow");
105     return (size_t)osz;
106   }
107 
108   Klass* element_klass();
109 
110 public:
111   // special iterators for index ranges, returns size of object
112   template <typename OopClosureType>
113   void oop_iterate_range(OopClosureType* blk, int start, int end);
114 };
115 
116 // See similar requirement for oopDesc.
117 static_assert(std::is_trivially_default_constructible<objArrayOopDesc>::value, "required");
118 
119 #endif // SHARE_OOPS_OBJARRAYOOP_HPP