// Copyright 2019 the V8 project 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 V8_LIBPLATFORM_DELAYED_TASK_QUEUE_H_

#define V8_LIBPLATFORM_DELAYED_TASK_QUEUE_H_

#include <map>

#include <memory>

#include <queue>

#include "include/libplatform/libplatform-export.h"

#include "src/base/platform/condition-variable.h"

#include "src/base/platform/time.h"

namespace v8 {

class Task;

namespace platform {

// DelayedTaskQueue provides queueing for immediate and delayed tasks. It does

// not provide any guarantees about ordering of tasks, except that immediate

// tasks will be run in the order that they are posted.

//

// This class is not thread-safe, and should be guarded by a lock.

class V8_PLATFORM_EXPORT DelayedTaskQueue {

public:

using TimeFunction = double (*)();

explicit DelayedTaskQueue(TimeFunction time_function);

~DelayedTaskQueue();

DelayedTaskQueue(const DelayedTaskQueue&) = delete;

DelayedTaskQueue& operator=(const DelayedTaskQueue&) = delete;

double MonotonicallyIncreasingTime();

// Appends an immediate task to the queue. The queue takes ownership of

// |task|. Tasks appended via this method will be run in order.

void Append(std::unique_ptr<Task> task);

// Appends a delayed task to the queue. There is no ordering guarantee

// provided regarding delayed tasks, both with respect to other delayed tasks

// and non-delayed tasks that were appended using Append().

void AppendDelayed(std::unique_ptr<Task> task, double delay_in_seconds);

struct MaybeNextTask {

enum { kTask, kWaitIndefinite, kWaitDelayed, kTerminated } state;

std::unique_ptr<Task> task;

base::TimeDelta wait_time;

};

// Returns the next task to process, or the amount of time to wait until the

// next delayed task. Returns nullptr if the queue is terminated. Will return

// either an immediate task posted using Append() or a delayed task where the

// deadline has passed, according to the |time_function| provided in the

// constructor.

MaybeNextTask TryGetNext();

// Terminate the queue.

void Terminate();

private:

std::unique_ptr<Task> PopTaskFromDelayedQueue(double now);

std::queue<std::unique_ptr<Task>> task_queue_;

std::multimap<double, std::unique_ptr<Task>> delayed_task_queue_;

bool terminated_ = false;

TimeFunction time_function_;

};

} // namespace platform

} // namespace v8

#endif // V8_LIBPLATFORM_DELAYED_TASK_QUEUE_H_