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// Copyright 2021 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_TASK_SEQUENCE_MANAGER_FENCE_H_
#define BASE_TASK_SEQUENCE_MANAGER_FENCE_H_
#include "base/base_export.h"
#include "base/compiler_specific.h"
#include "base/task/sequence_manager/enqueue_order.h"
#include "base/task/sequence_manager/task_order.h"
namespace base {
class TimeTicks;
namespace sequence_manager {
namespace internal {
class TaskQueueImpl;
// `Fence`s are used to prevent the execution of tasks starting with a
// particular `TaskOrder`, such that for a `Task` and a `Fence`, if
// task.task_order() >= fence.task_order(), then the task is blocked from
// running. Blocking fences are a special kind of fence that have a `TaskOrder`
// less than that of any `Task`.
class BASE_EXPORT Fence {
public:
// Creates a `Fence` with the same `TaskOrder` as `task_order`, which is
// useful for creating a fence relative to a particular `Task`.
// `task_order.enqueue_order()` must be "set", i.e. it cannot be
// `EnqueueOrder::none()`.
explicit Fence(const TaskOrder& task_order);
Fence(const Fence& other);
Fence& operator=(const Fence& other);
~Fence();
// Creates a blocking fence which has a `TaskOrder` that is less than that of
// all tasks.
static Fence BlockingFence();
const TaskOrder& task_order() const LIFETIME_BOUND { return task_order_; }
// Returns true iff this is a blocking fence.
bool IsBlockingFence() const {
return task_order_.enqueue_order() == EnqueueOrder::blocking_fence();
}
private:
friend class TaskQueueImpl; // For `CreateWithEnqueueOrder()`.
Fence(EnqueueOrder enqueue_order,
TimeTicks delayed_run_time,
int sequence_num);
// Creates a `Fence` with `enqueue_order` and a null delayed run time.
// `enqueue_order` cannot be EnqueueOrder::none().
static Fence CreateWithEnqueueOrder(EnqueueOrder enqueue_order);
TaskOrder task_order_;
};
} // namespace internal
} // namespace sequence_manager
} // namespace base
#endif // BASE_TASK_SEQUENCE_MANAGER_FENCE_H_
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