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Java User Space Schedule

Java User Space Schedule

March 10, 2025

A user-space scheduler manages tasks or “threads” entirely within an application, without relying on the operating system (OS) scheduler. This is different from kernel-level scheduling, where the OS manages threads. 什么是用户态调度？可以简单理解为自定义一堆任务, 由用户决定怎样执行这些任务。不涉及操作系统的进程/线程调度。

举例理解

Task 自定义的任务 

public class Task {
    private String name;
    private int steps;

    public Task(String name, int steps) {
        this.name = name;
        this.steps = steps;
    }

    public boolean runStep() {
        if (steps <= 0) return false; // Task is done
        System.out.println(name + " is running. Steps left: " + steps);
        steps--;
        return true; // Task has more work
    }
}

自定义的调度 

import java.util.LinkedList;
import java.util.Queue;

public class UserSpaceScheduler {
    // 以 FIFO 顺序执行 Task
    private Queue<Task> taskQueue = new LinkedList<>();

    public void addTask(Task task) {
        taskQueue.add(task);
    }

    public void run() {
        while (!taskQueue.isEmpty()) {
            Task task = taskQueue.poll();
            boolean hasMoreWork = task.runStep();
            if (hasMoreWork) {
//                deciding which task runs next
                taskQueue.add(task); // Re-add to the queue if not done
            }
        }
    }

}

Driver class 

public class Main {
    public static void main(String[] args) {
        UserSpaceScheduler scheduler = new UserSpaceScheduler();
        scheduler.addTask(new Task("Task A", 3));
        scheduler.addTask(new Task("Task B", 5));
        scheduler.addTask(new Task("Task C", 2));

        scheduler.run();
    }
}

如何工作

Cooperative Multitasking

Tasks are not OS threads. They are objects managed in a queue. 不是 OS 的线程

Explicit Yielding

The scheduler runs each task for one “step,” then moves to the next. Tasks don’t block—they voluntarily give up control.

No OS Involvement

The OS sees only the main thread running scheduler.run().

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