异步任务调度

时间 2019-11-12

标签异步任务调度繁體版

原文原文链接

问题

当客户端向服务层同时提交多个任务(Task)时，为了充分发挥服务器的处理计算能力，普通单线程已经不能知足咱们的需求了，须要采用多线程或多进程的技术来并发处理task，服务器在处理并发任务时须要知足一下几个要求：java

1.任务提交后，但愿服务器尽量快的处理并返回结果
2.多个任务同时处理时并不影响性能
3.当某个任务执行过程当中出错了，容许重试，而且不会阻碍其它task的处理

分析

1.多个任务同时提交，而且但愿服务器尽量快的处理并返回结果，采用多线程技术来实现，针对每一个任务，若是都分配一个线程去处理的话，那么当同时提交成千上万的任务的话，很容易致使服务器系统资源耗尽，服务器宕机。在分配任务时，建立和销毁线程很浪费资源，经过线程池技术来提升线程的执行效率，减去任务执行过程当中的线程建立和销毁的时间，大大提升任务执行效率。经过线程池技术，使得系统初始化时存放必定量的线程，客户端提交task给服务器后，将各个task分配给现有的空闲线程去处理，可是当提交不少task的话，很明显，线程池里面的线程数量也会不足，那如何解决呢？在客户端提交task到服务器后，现将task提交到任务队列中(TaskQueue),系统执行task时，从任务队列中提取task再分配给线程池中的空闲线程去执行任务。
2.当咱们发布任务后，任务交给了服务层取处理，在处理的过程当中不免会遇到一些特殊的问题，致使任务执行失败，为了保证任务能够有效的执行并实现咱们须要的任务，还须要为任务处理提供一个重试机制，这样当系统执行任务失败的时候，就能够启动重试机制来再次处理提交的任务，增长任务执行的成功率。

设计

Client
Client 模拟的是多个客户端，submit()方法用于提交task，提交的这个task类型为AsyncTask，该类为专用的任务类，下文会讲述。
AsyncExecutorService
首先这个类的目的是建立出一个线程池 executor来，用于资源分配，须要初始化一些参数，好比线程数量，最大线程数量，线程存活时长，重试次数以及重试等待时间等，这其中还有一个隐藏的参数--> 任务队列，分配资源时从任务队列中随机选择任务，进行分配，当有任务执行完成后，存在空闲线程时，该executor又会进行资源再分配，从任务队列总选择相应的任务进行执行。
该类还提供了执行任务的接口，从客户端传递过来的任务，在该类进行接收，并执行内部逻辑。
AsyncTask
AsyncTask是一个Runnable类，整正执行任务的地方，这行的任务经过抽象方法 doWork()对外提供，这样就能够实现不一样的任务操做。在该类中主要实现了重试机制的逻辑，当任务执行失败时进行相应次数的重试执行，保证任务执行成功。

代码

Client.java服务器

package com.ngsky.async;

/**
 * @Description TODO
 * @Author daxiong
 * @Date 7/7/2018 10:48 AM
 **/
public class AsyncTaskTest {
    public static void main(String[] args){
        AsyncExecutorService executorService = new AsyncExecutorService(5, 10, 30, TimeUnit.SECONDS, 2, 5);
        long beginTime = System.currentTimeMillis();
        for(int i = 0; i < 1000;i++){
            MockTask mockTask = new MockTask();
            mockTask.setName("task" + i);
            mockTask.setRetryTimes(3);
            mockTask.setRetryWaitTime(2000);
            executorService.execute(mockTask);
        }
        long endTime = System.currentTimeMillis();
        System.out.println("The task spend on " + ((endTime - beginTime) / 60L) + " minutes");
    }

}
// every task spend 20s, (1000 * 2) / 60 = 33 minutes
class MockTask extends AsyncTask{
    public void doWork() {
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

AsyncTask.java多线程

package com.ngsky.async;

/**
 * @Description TODO
 * @Author daxiong
 * @Date 7/7/2018 10:14 AM
 **/
public abstract class AsyncTask implements Runnable {

    private String name;  // task name
    private boolean successDone; // whether the task completed successful
    private int retryTimes;  // if the task was't finished successful, system allow retry to do the task for retrytimes
    private int retryWaitTime;  // system cant't retry to do work immediately, but execute after retryWaitTime

    public void run() {
        System.out.println("(task) " + getName() + " beginning execute....");
        long beginTime = System.currentTimeMillis();
        int currentRetryTimes = 1;
        try {
            doWork();
            System.out.println("(task) " + getName() + " completed successful!");
            this.setSuccessDone(true);
        } catch (Exception e) {
            System.out.println("(task) " + " execute filed..., message " + e);
            this.setSuccessDone(false);
        }
        if (getRetryTimes() <= 0) return;
        while (!isSuccessDone() && currentRetryTimes <= getRetryTimes()) {
            System.out.println("(task) " + "Executing retry " + currentRetryTimes + "th!" );
            if (getRetryWaitTime() > 0) {
                try {
                    Thread.sleep(getRetryWaitTime());
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            try {
                doWork();
                System.out.println("(task) " + getName() + " completed successful!");
                this.setSuccessDone(true);
            } catch (Exception e) {
                System.out.println("(task) " + getName() + " was failed, unknown reason! Please try again!");
                this.setSuccessDone(false);
                currentRetryTimes++;
            }
        }
        long endTime = System.currentTimeMillis();
        System.out.println("(task) " + " spend on " + (endTime - beginTime) + "ms and result is " + (this.isSuccessDone() ? "successful!" : "failed,Please check your task!"));
    }

    public abstract void doWork() throws Exception;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public boolean isSuccessDone() {
        return successDone;
    }

    public void setSuccessDone(boolean successDone) {
        this.successDone = successDone;
    }

    public int getRetryTimes() {
        return retryTimes;
    }

    public void setRetryTimes(int retryTimes) {
        this.retryTimes = retryTimes;
    }

    public int getRetryWaitTime() {
        return retryWaitTime;
    }

    public void setRetryWaitTime(int retryWaitTime) {
        this.retryWaitTime = retryWaitTime;
    }
}

AsyncExecutorService.java并发

package com.ngsky.async;

import java.util.concurrent.*;

/**
 * @Description async service interface
 * @Author daxiong
 * @Date 7/7/2018 9:16 AM
 **/
public class AsyncExecutorService {

    private int corePoolSize;
    private int maximumPoolSize;
    private long keepLiveTime;
    private TimeUnit timeUnit;
    private int retryTimes;
    private int retryWaitTime;
    private LinkedBlockingQueue<Runnable> blockingQueue;
    private ThreadPoolExecutor executor;

    public AsyncExecutorService(int corePoolSize, int maximumPoolSize, long keepLiveTimes,
                                TimeUnit timeUnit, int retryTimes, int retryWaitTimes){
        this.corePoolSize = corePoolSize;
        this.maximumPoolSize = maximumPoolSize;
        this.keepLiveTime = keepLiveTimes;
        this.timeUnit = timeUnit;
        this.retryTimes = retryTimes;
        this.retryWaitTime = retryWaitTimes;
        init();
    }

    private void init(){
        System.out.println("Async executor initializing...");
        blockingQueue = new LinkedBlockingQueue<Runnable>();
        executor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepLiveTime, timeUnit, blockingQueue);
    }

    // init task information
    private AsyncTask initTask(AsyncTask task){
        System.out.println("(task) " + task.getName() + " initializing...");
        if(retryTimes > 0) task.setRetryTimes(retryTimes);
        if(retryWaitTime > 0) task.setRetryWaitTime(retryWaitTime);
        return task;
    }

    public void execute(AsyncTask task){
        task = initTask(task);
        executor.execute(task);
    }

    public <T> Future<T> submit(Callable<T> job){
        return executor.submit(job);
    }

    public void shutdown(){
        if(executor != null)
            executor.shutdown();
    }

    public int getCorePoolSize() {
        return corePoolSize;
    }

    public void setCorePoolSize(int corePoolSize) {
        this.corePoolSize = corePoolSize;
    }

    public int getMaximumPoolSize() {
        return maximumPoolSize;
    }

    public void setMaximumPoolSize(int maximumPoolSize) {
        this.maximumPoolSize = maximumPoolSize;
    }

    public long getKeepLiveTime() {
        return keepLiveTime;
    }

    public void setKeepLiveTime(long keepLiveTime) {
        this.keepLiveTime = keepLiveTime;
    }

    public TimeUnit getTimeUnit() {
        return timeUnit;
    }

    public void setTimeUnit(TimeUnit timeUnit) {
        this.timeUnit = timeUnit;
    }

    public int getRetryTimes() {
        return retryTimes;
    }

    public void setRetryTimes(int retryTimes) {
        this.retryTimes = retryTimes;
    }

    public int getRetryWaitTime() {
        return retryWaitTime;
    }

    public void setRetryWaitTime(int retryWaitTime) {
        this.retryWaitTime = retryWaitTime;
    }

    public LinkedBlockingQueue<Runnable> getBlockingQueue() {
        return blockingQueue;
    }

    public void setBlockingQueue(LinkedBlockingQueue<Runnable> blockingQueue) {
        this.blockingQueue = blockingQueue;
    }

    public ThreadPoolExecutor getExecutor() {
        return executor;
    }

    public void setExecutor(ThreadPoolExecutor executor) {
        this.executor = executor;
    }
}

执行结果异步

总结

异步任务调度相关的理论和实现还有许多地方没有涉及到，这里作一个抛砖引玉，好比任务执行过程当中的拦截操做，线程池初始化时大小如何选择等等。async

任务调度针对的是高并发任务请求，要求保证系统性能，以最快的速度处理任务，提升处理效率和成功率。高并发

选择的技术：多线程，线程池，并发处理，任务调度，资源分配，重试机制。性能

再接再砺，写好每一篇博客，不要求天天写一篇，但要求每一篇都要是精华，都要饱含质量！this