1 /*

     2  * Copyright (c) 2017, 2018, 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_JFR_UTILITIES_JFRREFCOUNTPOINTER_HPP

    26 #define SHARE_VM_JFR_UTILITIES_JFRREFCOUNTPOINTER_HPP

    27 

    28 #include "jfr/utilities/jfrAllocation.hpp"

    29 #include "runtime/atomic.hpp"

    30 

    31 template <typename T>

    32 class RefCountHandle {

    33   template <typename, typename>

    34   friend class RefCountPointer;

    35  private:

    36   const T* _ptr;

    37 

    38   RefCountHandle(const T* ptr) : _ptr(ptr) {

    39     assert(_ptr != NULL, "invariant");

    40     _ptr->add_ref();

    41   }

    42 

    43  public:

    44   RefCountHandle() : _ptr(NULL) {}

    45 

    46   RefCountHandle(const RefCountHandle<T>& rhs) : _ptr(rhs._ptr) {

    47     if (_ptr != NULL) {

    48       _ptr->add_ref();

    49     }

    50   }

    51 

    52   ~RefCountHandle() {

    53     if (_ptr != NULL) {

    54       const T* temp = _ptr;

    55       _ptr = NULL;

    56       temp->remove_ref();

    57     }

    58   }

    59 

    60   // The copy-and-swap idiom upholds reference counting semantics

    61   void operator=(RefCountHandle<T> rhs) {

    62     const T* temp = rhs._ptr;

    63     rhs._ptr = _ptr;

    64     _ptr = temp;

    65   }

    66 

    67   bool operator==(const RefCountHandle<T>& rhs) const {

    68     return _ptr == rhs._ptr;

    69   }

    70 

    71   bool operator!=(const RefCountHandle<T>& rhs) const {

    72     return !operator==(rhs);

    73   }

    74 

    75   bool valid() const {

    76     return _ptr != NULL;

    77   }

    78 

    79   const T & operator->() const {

    80     return *_ptr;

    81   }

    82 

    83   T& operator->() {

    84     return *const_cast<T*>(_ptr);

    85   }

    86 };

    87 

    88 class MultiThreadedRefCounter {

    89  private:

    90   mutable volatile int _refs;

    91  public:

    92   MultiThreadedRefCounter() : _refs(0) {}

    93 

    94   void inc() const {

    95     Atomic::add(1, &_refs);

    96   }

    97 

    98   bool dec() const {

    99     return 0 == Atomic::add((-1), &_refs);

   100   }

   101 

   102   int current() const {

   103    return _refs;

   104   }

   105 };

   106 

   107 template <typename T, typename RefCountImpl = MultiThreadedRefCounter>

   108 class RefCountPointer : public JfrCHeapObj {

   109   template <typename>

   110   friend class RefCountHandle;

   111   typedef RefCountHandle<RefCountPointer<T, RefCountImpl> > RefHandle;

   112  private:

   113   const T* _ptr;

   114   mutable RefCountImpl _refs;

   115 

   116   // disallow multiple copies

   117   RefCountPointer(const RefCountPointer<T, RefCountImpl>& rhs);

   118   void operator=(const RefCountPointer<T, RefCountImpl>& rhs);

   119 

   120   ~RefCountPointer() {

   121     assert(_refs.current() == 0, "invariant");

   122     delete const_cast<T*>(_ptr);

   123   }

   124 

   125   void add_ref() const {

   126     _refs.inc();

   127   }

   128 

   129   void remove_ref() const {

   130     if (_refs.dec()) {

   131       delete this;

   132     }

   133   }

   134 

   135   RefCountPointer(const T* ptr) : _ptr(ptr), _refs() {

   136     assert(_ptr != NULL, "invariant");

   137   }

   138 

   139  public:

   140   const T* operator->() const {

   141     return _ptr;

   142   }

   143 

   144   T* operator->() {

   145     return const_cast<T*>(_ptr);

   146   }

   147 

   148   static RefHandle make(const T* ptr) {

   149     assert(ptr != NULL, "invariant");

   150     return RefHandle(new RefCountPointer<T, RefCountImpl>(ptr));

   151   }

   152 };

   153 

   154 #endif // SHARE_VM_JFR_UTILITIES_JFRREFCOUNTPOINTER_HPP