Add base::BindToTaskRunner and BindToCurrentThread

base/bind_to_task_runner.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 BASE_BIND_TO_TASK_RUNNER_H_
+#define BASE_BIND_TO_TASK_RUNNER_H_
+
+#include "base/bind.h"
+#include "base/bind_helpers.h"
+#include "base/callback.h"
+#include "base/location.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/scoped_vector.h"
+#include "base/task_runner.h"
+#include "base/thread_task_runner_handle.h"
+
+// This is a helper utility for Bind()ing callbacks to a given TaskRunner.
+// The typical use is when |a| (of class |A|) wants to hand a callback such as
+// base::Bind(&A::AMethod, a) to |b|, but needs to ensure that when |b| executes
+// the callback, it does so on a specific TaskRunner (for example, |a|'s current
+// MessageLoop).
+//
+// Typical usage: request to be called back on the current thread:
+// other->StartAsyncProcessAndCallMeBack(
+//    base::BindToTaskRunner(my_task_runner_, base::Bind(&MyClass::MyMethod,
+//                                                       this)));
+//
+// Note that like base::Bind(), BindToTaskRunner() can't bind non-constant
+// references, and that *unlike* base::Bind(), BindToTaskRunner() makes copies
+// of its arguments, and thus can't be used with arrays. Note that the callback
+// is always posted to the target TaskRunner.
+//
+// As a convenience, you can use base::BindToCurrentThread() to bind to the
+// TaskRunner for the current thread (ie, base::ThreadTaskRunnerHandle::Get()).
+
+namespace base {
+namespace internal {
+
+template <typename T>
+T& TrampolineForward(T& t) {
+  return t;
+}
+
+template <typename T, typename R>
+PassedWrapper<scoped_ptr<T, R>> TrampolineForward(scoped_ptr<T, R>& p) {
+  return Passed(&p);
+}
+
+template <typename T>
+PassedWrapper<ScopedVector<T>> TrampolineForward(ScopedVector<T>& p) {
+  return Passed(&p);
+}
+
+template <typename Sig>
+struct BindToTaskRunnerTrampoline;
+
+template <typename... Args>
+struct BindToTaskRunnerTrampoline<void(Args...)> {
+  static void Run(const scoped_refptr<TaskRunner>& task_runner,
+                  const Callback<void(Args...)>& cb,
+                  Args... args) {
+    task_runner->PostTask(FROM_HERE, Bind(cb, TrampolineForward(args)...));
+  }
+};
+
+}  // namespace internal
+
+template <typename T>
+Callback<T> BindToTaskRunner(const scoped_refptr<TaskRunner>& task_runner,
+                             const Callback<T>& cb) {
+  return Bind(&internal::BindToTaskRunnerTrampoline<T>::Run, task_runner, cb);
+}
+
+template <typename T>
+Callback<T> BindToCurrentThread(const Callback<T>& cb) {
+  return BindToTaskRunner(ThreadTaskRunnerHandle::Get(), cb);
+}
+
+}  // namespace base
+
+#endif  // BASE_BIND_TO_TASK_RUNNER_H_