Make mojo::Callback safe to copy across threads.

mojo/public/cpp/bindings/callback.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MOJO_PUBLIC_CPP_BINDINGS_CALLBACK_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_CALLBACK_H_
 
 #include <utility>
 
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
 #include "mojo/public/cpp/bindings/lib/callback_internal.h"
-#include "mojo/public/cpp/bindings/lib/shared_ptr.h"
 #include "mojo/public/cpp/bindings/lib/template_util.h"
 
 namespace mojo {
 
 template <typename Sig>
 class Callback;
 
 // Represents a callback with any number of parameters and no return value. The
 // callback is executed by calling its Run() method. The callback may be "null",
 // meaning it does nothing.
@@ skipping 11 matching lines @@
         // ForwardType).
         typename internal::Callback_ParamTraits<Args>::ForwardType...)
         const = 0;
   };
 
   // Constructs a "null" callback that does nothing.
   Callback() {}
 
   // Constructs a callback that will run |runnable|. The callback takes
   // ownership of |runnable|.
-  explicit Callback(Runnable* runnable) : sink_(runnable) {}
+  explicit Callback(Runnable* runnable) : sink_(new RunnableHolder(runnable)) {}
 
   // As above, but can take an object that isn't derived from Runnable, so long
   // as it has a compatible operator() or Run() method. operator() will be
   // preferred if the type has both.
   template <typename Sink>
   Callback(const Sink& sink) {
     using sink_type = typename internal::Conditional<
         internal::HasCompatibleCallOperator<Sink, Args...>::value,
         FunctorAdapter<Sink>, RunnableAdapter<Sink>>::type;
-    sink_ = internal::SharedPtr<Runnable>(new sink_type(sink));
+    sink_ = new RunnableHolder(new sink_type(sink));
   }
 
   // As above, but can take a compatible function pointer.
   Callback(void (*function_ptr)(
       typename internal::Callback_ParamTraits<Args>::ForwardType...))
-      : sink_(new FunctionPtrAdapter(function_ptr)) {}
+      : sink_(new RunnableHolder(new FunctionPtrAdapter(function_ptr))) {}
 
   // Executes the callback function.
   void Run(typename internal::Callback_ParamTraits<Args>::ForwardType... args)
       const {
-    if (sink_.get())
-      sink_->Run(std::forward<
+    if (sink_)
+      sink_->runnable->Run(std::forward<
                  typename internal::Callback_ParamTraits<Args>::ForwardType>(
           args)...);
   }
 
   bool is_null() const { return !sink_.get(); }
 
   // Resets the callback to the "null" state.
-  void reset() { sink_.reset(); }
+  void reset() { sink_ = nullptr; }
 
  private:
   // Adapts a class that has a Run() method but is not derived from Runnable to
   // be callable by Callback.
   template <typename Sink>
   struct RunnableAdapter : public Runnable {
     explicit RunnableAdapter(const Sink& sink) : sink(sink) {}
     virtual void Run(
         typename internal::Callback_ParamTraits<Args>::ForwardType... args)
         const override {
@@ skipping 32 matching lines @@
         typename internal::Callback_ParamTraits<Args>::ForwardType... args)
         const override {
       (*function_ptr)(
           std::forward<
               typename internal::Callback_ParamTraits<Args>::ForwardType>(
               args)...);
     }
     FunctionPtr function_ptr;
   };
 
-  internal::SharedPtr<Runnable> sink_;
+  struct RunnableHolder : public base::RefCountedThreadSafe<RunnableHolder> {
+    explicit RunnableHolder(Runnable* runnable) : runnable(runnable) {}
+
+    scoped_ptr<Runnable> runnable;
+
+   private:
+    ~RunnableHolder() {}
+    friend class base::RefCountedThreadSafe<RunnableHolder>;

[Sam McNally, 2016/03/19 01:03:53]

Friends before destructors.

[Anand Mistry (off Chromium), 2016/03/19 01:09:36]

Done.

+  };
+
+  scoped_refptr<RunnableHolder> sink_;
 };
 
 // A specialization of Callback which takes no parameters.
 typedef Callback<void()> Closure;
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_CALLBACK_H_