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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(scoped_refptr<SingleThreadTaskRunner> loop)
     23 //       : RefCountedDeleteOnMessageLoop<Foo>(std::move(loop)) {}
     24 //   ...
     25 //  private:
     26 //   friend class RefCountedDeleteOnMessageLoop<Foo>;
     27 //   friend class DeleteHelper<Foo>;
     28 //
     29 //   ~Foo();
     30 // };
     31 
     32 // TODO(skyostil): Rename this to RefCountedDeleteOnTaskRunner.
     33 template <class T>
     34 class RefCountedDeleteOnMessageLoop : public subtle::RefCountedThreadSafeBase {
     35  public:
     36   // This constructor will accept a MessageL00pProxy object, but new code should
     37   // prefer a SingleThreadTaskRunner. A SingleThreadTaskRunner for the
     38   // MessageLoop on the current thread can be acquired by calling
     39   // MessageLoop::current()->task_runner().
     40   RefCountedDeleteOnMessageLoop(
     41       scoped_refptr<SingleThreadTaskRunner> task_runner)
     42       : task_runner_(std::move(task_runner)) {
     43     DCHECK(task_runner_);
     44   }
     45 
     46   void AddRef() const {
     47     subtle::RefCountedThreadSafeBase::AddRef();
     48   }
     49 
     50   void Release() const {
     51     if (subtle::RefCountedThreadSafeBase::Release())
     52       DestructOnMessageLoop();
     53   }
     54 
     55  protected:
     56   friend class DeleteHelper<RefCountedDeleteOnMessageLoop>;
     57   ~RefCountedDeleteOnMessageLoop() {}
     58 
     59   void DestructOnMessageLoop() const {
     60     const T* t = static_cast<const T*>(this);
     61     if (task_runner_->BelongsToCurrentThread())
     62       delete t;
     63     else
     64       task_runner_->DeleteSoon(FROM_HERE, t);
     65   }
     66 
     67   scoped_refptr<SingleThreadTaskRunner> task_runner_;
     68 
     69  private:
     70   DISALLOW_COPY_AND_ASSIGN(RefCountedDeleteOnMessageLoop);
     71 };
     72 
     73 }  // namespace base
     74 
     75 #endif  // BASE_MEMORY_REF_COUNTED_DELETE_ON_MESSAGE_LOOP_H_
     76