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      1 // Copyright 2013 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_MEMORY_REF_COUNTED_DELETE_ON_MESSAGE_LOOP_H_
      6 #define BASE_MEMORY_REF_COUNTED_DELETE_ON_MESSAGE_LOOP_H_
      7 
      8 #include "base/location.h"
      9 #include "base/logging.h"
     10 #include "base/macros.h"
     11 #include "base/memory/ref_counted.h"
     12 #include "base/single_thread_task_runner.h"
     13 
     14 namespace base {
     15 
     16 // RefCountedDeleteOnMessageLoop is similar to RefCountedThreadSafe, and ensures
     17 // that the object will be deleted on a specified message loop.
     18 //
     19 // Sample usage:
     20 // class Foo : public RefCountedDeleteOnMessageLoop<Foo> {
     21 //
     22 //   Foo(const scoped_refptr<SingleThreadTaskRunner>& loop)
     23 //       : RefCountedDeleteOnMessageLoop<Foo>(loop) {
     24 //     ...
     25 //   }
     26 //   ...
     27 //  private:
     28 //   friend class RefCountedDeleteOnMessageLoop<Foo>;
     29 //   friend class DeleteHelper<Foo>;
     30 //
     31 //   ~Foo();
     32 // };
     33 
     34 // TODO(skyostil): Rename this to RefCountedDeleteOnTaskRunner.
     35 template <class T>
     36 class RefCountedDeleteOnMessageLoop : public subtle::RefCountedThreadSafeBase {
     37  public:
     38   // This constructor will accept a MessageL00pProxy object, but new code should
     39   // prefer a SingleThreadTaskRunner. A SingleThreadTaskRunner for the
     40   // MessageLoop on the current thread can be acquired by calling
     41   // MessageLoop::current()->task_runner().
     42   RefCountedDeleteOnMessageLoop(
     43       const scoped_refptr<SingleThreadTaskRunner>& task_runner)
     44       : task_runner_(task_runner) {
     45     DCHECK(task_runner_);
     46   }
     47 
     48   void AddRef() const {
     49     subtle::RefCountedThreadSafeBase::AddRef();
     50   }
     51 
     52   void Release() const {
     53     if (subtle::RefCountedThreadSafeBase::Release())
     54       DestructOnMessageLoop();
     55   }
     56 
     57  protected:
     58   friend class DeleteHelper<RefCountedDeleteOnMessageLoop>;
     59   ~RefCountedDeleteOnMessageLoop() {}
     60 
     61   void DestructOnMessageLoop() const {
     62     const T* t = static_cast<const T*>(this);
     63     if (task_runner_->BelongsToCurrentThread())
     64       delete t;
     65     else
     66       task_runner_->DeleteSoon(FROM_HERE, t);
     67   }
     68 
     69   scoped_refptr<SingleThreadTaskRunner> task_runner_;
     70 
     71  private:
     72   DISALLOW_COPY_AND_ASSIGN(RefCountedDeleteOnMessageLoop);
     73 };
     74 
     75 }  // namespace base
     76 
     77 #endif  // BASE_MEMORY_REF_COUNTED_DELETE_ON_MESSAGE_LOOP_H_
     78