native_client_sdk/src/libraries/sdk_util/ref_object.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef LIBRARIES_SDK_UTIL_REF_OBJECT
   6 #define LIBRARIES_SDK_UTIL_REF_OBJECT
   7
   8 #include <stdlib.h>
   9 #include "pthread.h"
  10
  11 #include "sdk_util/atomicops.h"
  12
  13 namespace sdk_util {
  14
  15 class ScopedRefBase;
  16
  17 /*
  18  * RefObject
  19  *
  20  * A reference counted object. RefObjects should only be handled by ScopedRef
  21  * objects.
  22  *
  23  * When the object is first created, it has a reference count of zero.  It's
  24  * first incremented when it gets assigned to a ScopedRef.  When the last
  25  * ScopedRef is reset or destroyed the object will get released.
  26  */
  27
  28 class RefObject {
  29  public:
  30   RefObject() {
  31     ref_count_ = 0;
  32   }
  33
  34   /*
  35    * RefCount
  36    *
  37    * RefCount returns an instantaneous snapshot of the RefCount, which may
  38    * change immediately after it is fetched.  This is only stable when all
  39    * pointers to the object are scoped pointers (ScopedRef), and the value
  40    * is one implying the current thread is the only one, with visibility to
  41    * the object.
  42    */
  43   int RefCount() const { return ref_count_; }
  44
  45  protected:
  46   virtual ~RefObject() {}
  47
  48   // Override to clean up object when last reference is released.
  49   virtual void Destroy() {}
  50
  51   void Acquire() {
  52     AtomicAddFetch(&ref_count_, 1);
  53   }
  54
  55   bool Release() {
  56     Atomic32 val = AtomicAddFetch(&ref_count_, -1);
  57     if (val == 0) {
  58       Destroy();
  59       delete this;
  60       return false;
  61     }
  62     return true;
  63   }
  64
  65  private:
  66   Atomic32 ref_count_;
  67
  68   friend class ScopedRefBase;
  69 };
  70
  71 }  // namespace sdk_util
  72
  73 #endif  // LIBRARIES_SDK_UTIL_REF_OBJECT
  74