1 /*
   2  * Copyright (c) 2016, 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_GC_G1_G1FIXEDSIZESTACK_HPP
  26 #define SHARE_VM_GC_G1_G1FIXEDSIZESTACK_HPP
  27 
  28 #include "memory/allocation.hpp"
  29 #include "utilities/debug.hpp"
  30 #include "utilities/globalDefinitions.hpp"
  31 
  32 // Base class for a fixed size stack, i.e. its backing array is of fixed size. Collects
  33 // methods common to any instances of the array. The backing array is preallocated
  34 // on the C heap.
  35 //
  36 // Pushing elements and access to elements below _length is MT safe. Any other
  37 // operations modifying it are not.
  38 class G1FixedSizeStackBase : public CHeapObj<mtGC> {
  39 protected:
  40   address _base;           // The real base address.
  41   size_t _max_length;      // The length of the array.
  42 
  43   // Current number of elements pushed. The MSB of this value is also used to
  44   // indicate that a concurrent writer is currently pushing to it.
  45   size_t volatile _length;
  46 
  47   static const size_t LengthMask = ~nth_bit(BitsPerWord - 1);
  48   
  49 protected:
  50 
  51   G1FixedSizeStackBase() : _base(NULL), _max_length(0), _length(0) { }
  52 
  53   // Allocate and initialize the backing array.
  54   void initialize(size_t max_length, size_t elem_size);
  55 
  56   void verify_index(size_t index) const PRODUCT_RETURN;
  57 
  58 public:
  59   virtual ~G1FixedSizeStackBase();
  60 
  61   size_t max_length() const { return _max_length; }
  62   inline size_t length() const;
  63 };
  64 
  65 template<class T>
  66 class G1FixedSizeStack : public G1FixedSizeStackBase {
  67 private:
  68   T* base() const { return (T*)G1FixedSizeStackBase::_base; }
  69 
  70   // Set the element of the given array at the given index to the
  71   // given value. Assume the index is valid.
  72   void set_by_index_raw(size_t index, T const value) {
  73     this->base()[index] = value;
  74   }
  75 
  76 public:
  77   // Return the element of the array at the given index. Assume
  78   // the index is valid. This is a convenience method that does sanity
  79   // checking on the index.
  80   T get_by_index(size_t index) const {
  81     verify_index(index);
  82     return this->base()[index];
  83   }
  84 
  85   void clear() {
  86 #ifdef ASSERT
  87     _length = _max_length;
  88     for (size_t i = 0; i < _max_length; i++) {
  89       set_by_index_raw(i, T());
  90     }
  91 #endif
  92     _length = 0;
  93   }
  94 
  95   G1FixedSizeStack() : G1FixedSizeStackBase() {}
  96 
  97   void initialize(size_t max_length) {
  98     G1FixedSizeStackBase::initialize(max_length, sizeof(T));
  99     this->clear();
 100   }
 101 
 102   inline void par_push(T const elem);
 103 };
 104 
 105 #endif // SHARE_VM_GC_G1_G1FIXEDSIZESTACK_HPP