media: Add RunOnDestruction

media/base/run_on_destruction.h

+// Copyright 2015 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 MEDIA_BASE_RUN_ON_DESTRUCTION_H_
+#define MEDIA_BASE_RUN_ON_DESTRUCTION_H_
+
+#include <memory>
+
+#include "base/callback_forward.h"
+#include "base/bind.h"
+#include "base/tuple.h"
+#include "base/memory/ptr_util.h"
+
+// This is a helper utility to wrap a base::Callback such that if the
+// callback is destructed before it has a chance to run (e.g. the callback is
+// bound into a task in a task runner and the task is dropped), it will be run
+// with a set of parameters passed into RunOnDestruction.
+//
+// Typical usage:
+//   foo->DoWorkAndReturnResult(
+//     media::RunOnDestruction(base::Bind(&Foo::OnResult, this), false));
+//
+// If the callback is destructed without running, it'll be called with "false".
+
+// TODO(xhwang): This class really only makes sense for base::OnceCallback.
+// However, mojo uses base::Callback in generated interfaces.
+
+
+namespace media {
+namespace internal {
+
+template <typename CallbackType, typename Tuple, size_t... Ns>
+inline void DispatchToCallbackImpl(CallbackType callback,
+                                   Tuple&& args,
+                                   base::IndexSequence<Ns...>) {
+  std::move(callback).Run(base::get<Ns>(std::forward<Tuple>(args))...);
+}
+
+template <typename CallbackType, typename Tuple>
+inline void DispatchToCallback(CallbackType callback, Tuple&& args) {
+  DispatchToCallbackImpl(std::move(callback), std::forward<Tuple>(args),
+                         base::MakeIndexSequenceForTuple<Tuple>());
+}
+
+// First, tell the compiler RunOnDestructionHelper is a struct template with one
+// type parameter.  Then define specializations where the type is a function
+// returning void and taking zero or more arguments.
+template <typename Signature>
+class RunOnDestructionHelper;
+
+template <typename... Args>
+class RunOnDestructionHelper<void(Args...)> {
+ public:
+  using CallbackType = base::Callback<void(Args...)>;
+
+  RunOnDestructionHelper(CallbackType callback, Args... args)
+      : callback_(std::move(callback)),
+        args_(std::make_tuple(args...)) {
+    DCHECK(callback_);
+  }
+
+  inline void Run(Args... args);
+
+  ~RunOnDestructionHelper() {
+    if (callback_)
+      DispatchToCallback(std::move(callback_), args_);
+  }
+
+ private:
+  CallbackType callback_;
+  std::tuple<Args...> args_;
+};
+
+template <typename... Args>
+inline void RunOnDestructionHelper<void(Args...)>::Run(Args... args) {
+  std::move(callback_).Run(args...);
+}
+
+}  // namespace internal
+
+template <typename T, typename... Args>
+inline base::Callback<T> RunOnDestruction(base::Callback<T> cb, Args... args) {
+  return base::Bind(
+      &internal::RunOnDestructionHelper<T>::Run,
+      base::MakeUnique<internal::RunOnDestructionHelper<T>>(
+          std::move(cb), args...));
+}
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_RUN_ON_DESTRUCTION_H_