base/supports_user_data.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 BASE_SUPPORTS_USER_DATA_H_
   6 #define BASE_SUPPORTS_USER_DATA_H_
   7
   8 #include <map>
   9
  10 #include "base/base_export.h"
  11 #include "base/memory/linked_ptr.h"
  12 #include "base/memory/ref_counted.h"
  13 #include "base/threading/thread_checker.h"
  14
  15 namespace base {
  16
  17 // This is a helper for classes that want to allow users to stash random data by
  18 // key. At destruction all the objects will be destructed.
  19 class BASE_EXPORT SupportsUserData {
  20  public:
  21   SupportsUserData();
  22
  23   // Derive from this class and add your own data members to associate extra
  24   // information with this object. Alternatively, add this as a public base
  25   // class to any class with a virtual destructor.
  26   class BASE_EXPORT Data {
  27    public:
  28     virtual ~Data() {}
  29   };
  30
  31   // The user data allows the clients to associate data with this object.
  32   // Multiple user data values can be stored under different keys.
  33   // This object will TAKE OWNERSHIP of the given data pointer, and will
  34   // delete the object if it is changed or the object is destroyed.
  35   Data* GetUserData(const void* key) const;
  36   void SetUserData(const void* key, Data* data);
  37   void RemoveUserData(const void* key);
  38
  39   // SupportsUserData is not thread-safe, and on debug build will assert it is
  40   // only used on one thread. Calling this method allows the caller to hand
  41   // the SupportsUserData instance across threads. Use only if you are taking
  42   // full control of the synchronization of that hand over.
  43   void DetachUserDataThread();
  44
  45  protected:
  46   virtual ~SupportsUserData();
  47
  48  private:
  49   typedef std::map<const void*, linked_ptr<Data> > DataMap;
  50
  51   // Externally-defined data accessible by key.
  52   DataMap user_data_;
  53   // Guards usage of |user_data_|
  54   ThreadChecker thread_checker_;
  55
  56   DISALLOW_COPY_AND_ASSIGN(SupportsUserData);
  57 };
  58
  59 // Adapter class that releases a refcounted object when the
  60 // SupportsUserData::Data object is deleted.
  61 template <typename T>
  62 class UserDataAdapter : public base::SupportsUserData::Data {
  63  public:
  64   static T* Get(SupportsUserData* supports_user_data, const void* key) {
  65     UserDataAdapter* data =
  66       static_cast<UserDataAdapter*>(supports_user_data->GetUserData(key));
  67     return data ? static_cast<T*>(data->object_.get()) : NULL;
  68   }
  69
  70   UserDataAdapter(T* object) : object_(object) {}
  71   T* release() { return object_.release(); }
  72
  73  private:
  74   scoped_refptr<T> object_;
  75
  76   DISALLOW_COPY_AND_ASSIGN(UserDataAdapter);
  77 };
  78
  79 }  // namespace base
  80
  81 #endif  // BASE_SUPPORTS_USER_DATA_H_