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// Copyright (c) 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_BIND_TO_CURRENT_LOOP_H_
#define MEDIA_BASE_BIND_TO_CURRENT_LOOP_H_
#include "base/bind.h"
#include "base/location.h"
#include "base/memory/scoped_vector.h"
#include "base/single_thread_task_runner.h"
#include "base/thread_task_runner_handle.h"
// This is a helper utility for base::Bind()ing callbacks to the current
// MessageLoop. 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|'s current MessageLoop.
//
// Typical usage: request to be called back on the current thread:
// other->StartAsyncProcessAndCallMeBack(
// media::BindToCurrentLoop(base::Bind(&MyClass::MyMethod, this)));
//
// Note that like base::Bind(), BindToCurrentLoop() can't bind non-constant
// references, and that *unlike* base::Bind(), BindToCurrentLoop() makes copies
// of its arguments, and thus can't be used with arrays.
namespace media {
// Mimic base::internal::CallbackForward, replacing std::move(p) with
// base::Passed(&p) to account for the extra layer of indirection.
namespace internal {
template <typename T>
T& TrampolineForward(T& t) { return t; }
template <typename T, typename R>
base::internal::PassedWrapper<scoped_ptr<T, R> > TrampolineForward(
scoped_ptr<T, R>& p) { return base::Passed(&p); }
template <typename T>
base::internal::PassedWrapper<ScopedVector<T> > TrampolineForward(
ScopedVector<T>& p) { return base::Passed(&p); }
// First, tell the compiler TrampolineHelper 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 Sig> struct TrampolineHelper;
template <typename... Args>
struct TrampolineHelper<void(Args...)> {
static void Run(
const scoped_refptr<base::SingleThreadTaskRunner>& task_runner,
const base::Callback<void(Args...)>& cb,
Args... args) {
task_runner->PostTask(FROM_HERE,
base::Bind(cb, TrampolineForward(args)...));
}
};
} // namespace internal
template<typename T>
static base::Callback<T> BindToCurrentLoop(
const base::Callback<T>& cb) {
return base::Bind(&internal::TrampolineHelper<T>::Run,
base::ThreadTaskRunnerHandle::Get(), cb);
}
} // namespace media
#endif // MEDIA_BASE_BIND_TO_CURRENT_LOOP_H_
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