wait/notify模拟线程池

线程创建和销毁会消耗很多的资源，当我们创建线程时，会发现cpu利用率很高，为了节省资源的使用，使用线程池是一个比较好的选择，当有任务需要执行时，随机分配给一条线程去执行，也可以删除任务，获取任务数量等。下面使用springboot构建一个简单的线程池。

自定义线程池

package com.demo.bootdemo.threadpool;

import java.util.LinkedList;
import java.util.List;

public class MyThreadPool {
    // 线程用于执行任务，所以要具有执行任务，添加线程，减少线程，获取任务数量，释放线程，定时执行任务等操作
    private LinkedList<Thread> threadPool = new LinkedList<Thread>();
    // 存放需要执行的任务
    private LinkedList<Job> jobs = new LinkedList<Job>();
    // 线程池容量
    private int capacity;

    public MyThreadPool() {
        capacity = 10;
        init();
    }

    public MyThreadPool(int capacity) {
        this.capacity = capacity;
        init();
    }

    /**
     * 初始化
     */
    private void init() {
        for (int i = 0; i < capacity; i++) {
            Thread th = new Thread(new MyRunnable(), "th_" + i);
            threadPool.add(th);
            th.start();
        }
    }

    /**
     * 执行单个任务
     *
     * @param job
     */
    public void executeJob(Job job) {
        addJob(job);
    }

    /**
     * 批量执行任务
     *
     * @param jobList
     */
    public void executeJobs(List<Job> jobList) {
        addJobs(jobList);
    }

    public void deleteJob(String jobKey) {
        synchronized (jobs) {
            Job delJob = null;
            for (Job j : jobs) {
                if (jobKey.equals(j.getJobKey())) {
                    delJob = j;
                    break;
                }
            }
            // 删除
            jobs.remove(delJob);
        }
    }

    private void addJobs(List<Job> jobList) {
        synchronized (jobs) {
            if (jobList != null && jobList.size() > 0) {
                jobs.addAll(jobList);
                jobs.notifyAll();
            }
        }
    }

    private void addJob(Job job) {
        synchronized (jobs) {
            jobs.add(job);
            jobs.notify();
        }
    }

    /**
     * 获取任务数量
     *
     * @return
     */
    public int getJobSize() {
        return jobs.size();
    }

    private class MyRunnable implements Runnable {
        public void run() {
            // 任务列表中没有任务，则等待，否则取出任务执行
            while (true) {
                Job job = null;
                synchronized (jobs) {
                    if (jobs.isEmpty()) {
                        try {
                            jobs.wait();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    } else {
                        job = jobs.removeFirst();
                    }
                }
                if (job != null) {
                    job.execute();
                }
            }
        }
    }
}

Job接口

package com.demo.bootdemo.threadpool;

public abstract class Job {

    String jobKey;

    public String getJobKey() {
        return jobKey;
    }

    public void setJobKey(String jobKey) {
        this.jobKey = jobKey;
    }
    public abstract void execute();
}

Job实现类，这里模仿了三种不同类型的Job, PrintJob,SayHelloJob和WriteFileJob

PrintJob

package com.demo.bootdemo.threadpool.myjob;

import java.util.LinkedList;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.demo.bootdemo.threadpool.Job;

public class PrintJob extends Job {
    private Logger logger = LoggerFactory.getLogger(PrintJob.class);
    private LinkedList<String> ls = new LinkedList<String>();

    public PrintJob(String jobKey, LinkedList<String> ls) {
        this.setJobKey(jobKey);
        this.ls = ls;
    }

    @Override
    public void execute() {
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        logger.info(ls.toString() +", " + getJobKey());
    }

}

SayHelloJob

package com.demo.bootdemo.threadpool.myjob;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.demo.bootdemo.threadpool.Job;

public class SayHelloJob extends Job {
    private Logger logger = LoggerFactory.getLogger(SayHelloJob.class);

    public SayHelloJob(String jobKey) {
        this.setJobKey(jobKey);
    }

    @Override
    public void execute() {
        logger.info("Just say hello. " + getJobKey());
    }

}

WriteFileJob

package com.demo.bootdemo.threadpool.myjob;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.demo.bootdemo.threadpool.Job;

public class WriteFileJob extends Job {

    private Logger logger = LoggerFactory.getLogger(WriteFileJob.class);

    public WriteFileJob(String jobKey) {
        this.setJobKey(jobKey);
    }

    @Override
    public void execute() {
        String fileName = "./" + System.currentTimeMillis();
        File f = new File(fileName);
        FileOutputStream fos = null;
        try {
            fos = new FileOutputStream(f);
            fos.write(String.valueOf(System.currentTimeMillis()).getBytes());
            Thread.sleep(1000);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (fos != null) {
                try {
                    fos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            logger.info(String.format("write file. fileName: %s", fileName) + ", " + getJobKey());
        }
    }

}

配置类

package com.demo.bootdemo.threadpool.properties;

import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.Configuration;

@Configuration
@ConfigurationProperties(prefix = "pool.thread")
public class ThreadPoolProperties {

    private int count;

    public int getCount() {
        return count;
    }

    public void setCount(int count) {
        this.count = count;
    }

}

配置文件applicaiton.properties

pool.thread.count=5

测试类入口

package com.demo.bootdemo.threadpool.listeners;

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;

import org.springframework.context.ApplicationListener;
import org.springframework.context.event.ContextRefreshedEvent;

import com.demo.bootdemo.threadpool.Job;
import com.demo.bootdemo.threadpool.MyThreadPool;
import com.demo.bootdemo.threadpool.myjob.PrintJob;
import com.demo.bootdemo.threadpool.myjob.SayHelloJob;
import com.demo.bootdemo.threadpool.myjob.WriteFileJob;
import com.demo.bootdemo.threadpool.properties.ThreadPoolProperties;

public class ThreadPoolListeners implements ApplicationListener<ContextRefreshedEvent> {

    @Override
    public void onApplicationEvent(ContextRefreshedEvent event) {
        ThreadPoolProperties bean = event.getApplicationContext().getBean(ThreadPoolProperties.class);
        // 初始化线程池
        MyThreadPool pool = new MyThreadPool(bean.getCount());
        // 新建PrintJob任务
        LinkedList<String> ls = new LinkedList<String>();
        ls.add("a");
        ls.add("b");
        PrintJob printJob = new PrintJob("PrintJobKey000", ls);

        // 新建sayhellojob
        SayHelloJob sayHelloJob = new SayHelloJob("SayHelloJobKey000");

        // 新建writeFileJob
        WriteFileJob writeFileJob = new WriteFileJob("WriteFileJobKey000");

        List<Job> jobList = new ArrayList<>();
        jobList.add(printJob);
        jobList.add(sayHelloJob);
        jobList.add(writeFileJob);

        // 执行以上三个任务
        pool.executeJobs(jobList);

        jobList.clear();
        for (int i = 0; i < 10; i++) {
            sayHelloJob = new SayHelloJob("sayhellojobkey" + i);
            jobList.add(sayHelloJob);
        }
        pool.executeJobs(jobList);

        // 删除任务
        pool.deleteJob("sayhellojobkey7");
        pool.deleteJob("sayhellojobkey8");

        // 单独执行一个任务
        writeFileJob = new WriteFileJob("writeJobkey_alone");
        pool.executeJob(writeFileJob);

    }

}

springboot启动类

package com.demo.bootdemo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

import com.demo.bootdemo.threadpool.listeners.ThreadPoolListeners;

@SpringBootApplication
public class MythreadpoolApplication {

    public static void main(String[] args) {
        SpringApplication springApplication = new SpringApplication(MythreadpoolApplication.class);
        springApplication.addListeners(new ThreadPoolListeners());
        springApplication.run(args);

    }

}

输出结果

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.1.1.RELEASE)

20:39:18.382 [main] Starting MythreadpoolApplication on admin-PC with PID 27632 (D:\Programs\eclipseworkplace\springboot\mythreadpool\target\classes started by admin in D:\Programs\eclipseworkplace\springboot\mythreadpool)
20:39:18.385 [main] No active profile set, falling back to default profiles: default
20:39:18.855 [th_3] Just say hello. SayHelloJobKey000
20:39:18.855 [th_3] Just say hello. sayhellojobkey1
20:39:18.855 [th_3] Just say hello. sayhellojobkey2
20:39:18.855 [th_0] Just say hello. sayhellojobkey0
20:39:18.855 [th_3] Just say hello. sayhellojobkey3
20:39:18.855 [th_0] Just say hello. sayhellojobkey5
20:39:18.855 [th_0] Just say hello. sayhellojobkey6
20:39:18.855 [th_0] Just say hello. sayhellojobkey9
20:39:18.855 [th_1] Just say hello. sayhellojobkey4
20:39:18.858 [main] Started MythreadpoolApplication in 0.722 seconds (JVM running for 1.432)
20:39:19.854 [th_4] [a, b], PrintJobKey000
20:39:19.857 [th_2] write file. fileName: ./1558355958854, WriteFileJobKey000
20:39:19.858 [th_0] write file. fileName: ./1558355958855, writeJobkey_alone

从述打印日志看，sayhellojobkey7和sayhellojobkey8对应jobkey未打印出来，删除任务生效，所有任务都正常执行，两个WriteFileJob分别生成名称为1558355958854和1558355958855的文件，查看当前路径，也确实可以找到这样的文件。

将本案例打包，放入linux执行，使用jstack查看所有线程状态

这些线程基本上都处于WAITING状态，不具有锁，待Job任务被添加到集合中时，将唤醒这些线程，处理Job