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// Copyright 2020 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_POST_TASK_INTERNAL_H_
#define BASE_BIND_POST_TASK_INTERNAL_H_
#include <utility>
#include "base/bind.h"
#include "base/callback.h"
#include "base/location.h"
#include "base/memory/ref_counted.h"
#include "base/task_runner.h"
namespace base {
namespace internal {
// Helper class to ensure that the input callback is always invoked and
// destroyed on the provided task runner.
template <typename CallbackType>
class BindPostTaskTrampoline {
public:
BindPostTaskTrampoline(scoped_refptr<TaskRunner> task_runner,
const Location& location,
CallbackType callback)
: task_runner_(std::move(task_runner)),
location_(location),
callback_(std::move(callback)) {
DCHECK(task_runner_);
// Crash immediately instead of when trying to Run() `callback_` on the
// destination `task_runner_`.
CHECK(callback_);
}
BindPostTaskTrampoline(const BindPostTaskTrampoline& other) = delete;
BindPostTaskTrampoline& operator=(const BindPostTaskTrampoline& other) =
delete;
~BindPostTaskTrampoline() {
if (callback_) {
// Post a task to ensure that `callback_` is destroyed on `task_runner_`.
// The callback's BindState may own an object that isn't threadsafe and is
// unsafe to destroy on a different task runner.
//
// Note that while this guarantees `callback_` will be destroyed when the
// posted task runs, it doesn't guarantee the ref-counted BindState is
// destroyed at the same time. If the callback was copied before being
// passed to BindPostTaskTrampoline then the BindState can outlive
// `callback_`, so the user must ensure any other copies of the callback
// are also destroyed on the correct task runner.
task_runner_->PostTask(location_, BindOnce(&DestroyCallbackOnTaskRunner,
std::move(callback_)));
}
}
template <typename... Args>
void Run(Args... args) {
// GetClosure() consumes `callback_`.
task_runner_->PostTask(location_,
GetClosure(&callback_, std::forward<Args>(args)...));
}
private:
static OnceClosure GetClosure(OnceClosure* callback) {
// `callback` is already a closure, no need to call BindOnce().
return std::move(*callback);
}
template <typename... Args>
static OnceClosure GetClosure(OnceCallback<void(Args...)>* callback,
Args&&... args) {
return BindOnce(std::move(*callback), std::forward<Args>(args)...);
}
static void DestroyCallbackOnTaskRunner(CallbackType callback) {}
const scoped_refptr<TaskRunner> task_runner_;
const Location location_;
CallbackType callback_;
};
} // namespace internal
} // namespace base
#endif // BASE_BIND_POST_TASK_INTERNAL_H_
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