【为什么需要多线程】

作者: hello高world | 来源:发表于2017-01-14 21:43 被阅读0次

本文代码会在后期整理上传到github中

1. 没有使用多线程情况

代码：

package com.tinygao.thread;
import com.google.common.base.Stopwatch;
import com.tinygao.thread.executor.JobExecutionFactory;
import com.tinygao.thread.job.DBJob;
import com.tinygao.thread.job.FileJob;
import com.tinygao.thread.job.Job;
import com.tinygao.thread.job.JobType;
import lombok.extern.slf4j.Slf4j;
import java.net.URI;
import java.util.concurrent.TimeUnit;
@Slf4j
public class ExecutionSingleClient {
    public static void main(String[] args) throws Exception {
        final Stopwatch stopwatch = Stopwatch.createStarted();
        runDBJob();
        runFileJob();
        log.info("total elapse time {}s", stopwatch.elapsed(TimeUnit.SECONDS));
        stopwatch.stop();
    }

    private static void runDBJob() throws Exception {
        //创建一个任务
        Job dbJob = new DBJob("select * from tbl_user");
        //创建一个数据库执行者
        Execution dbExecution = new Execution(
                dbJob,
                JobExecutionFactory.createInstance(JobType.DB_JOB));
        dbExecution.call();
    }

    private static void runFileJob() throws Exception {
        //创建一个任务
        Job fileJob = new FileJob(new URI("file://d:"));
        //创建一个文件执行者
        Execution fileExecution = new Execution(
                fileJob,
                JobExecutionFactory.createInstance(JobType.FILE_JOB));
        fileExecution.call();
    }
}

输出：

2017-01-14 21:34:40.129 [main] INFO com.tinygao.thread.job.Job - DB_JOB job status : STARTING， elapse time : 0s
2017-01-14 21:34:40.129 [main] INFO com.tinygao.thread.job.Job - DB_JOB job status : RUNNING， elapse time : 0s
2017-01-14 21:34:41.183 [main] INFO com.tinygao.thread.job.Job - DB_JOB job status : RUNNING， elapse time : 1s
2017-01-14 21:34:42.184 [main] INFO com.tinygao.thread.job.Job - DB_JOB job status : RUNNING， elapse time : 2s
2017-01-14 21:34:43.185 [main] INFO com.tinygao.thread.job.Job - DB_JOB job status : RUNNING， elapse time : 3s
2017-01-14 21:34:44.187 [main] INFO com.tinygao.thread.job.Job - DB_JOB job status : RUNNING， elapse time : 4s
2017-01-14 21:34:45.189 [main] INFO com.tinygao.thread.job.Job - DB_JOB job status : RUNNING， elapse time : 5s
2017-01-14 21:34:46.191 [main] INFO com.tinygao.thread.job.Job - DB_JOB job status : RUNNING， elapse time : 6s
2017-01-14 21:34:47.193 [main] INFO com.tinygao.thread.job.Job - DB_JOB job status : RUNNING， elapse time : 7s
2017-01-14 21:34:48.194 [main] INFO com.tinygao.thread.job.Job - DB_JOB job status : RUNNING， elapse time : 8s
2017-01-14 21:34:49.196 [main] INFO com.tinygao.thread.job.Job - DB_JOB job status : RUNNING， elapse time : 9s
2017-01-14 21:34:50.198 [main] INFO com.tinygao.thread.job.Job - DB_JOB job status : RUNNING， elapse time : 10s
2017-01-14 21:34:50.198 [main] INFO com.tinygao.thread.job.Job - DB_JOB job status : FINISHED， elapse time : 10s
2017-01-14 21:34:50.198 [main] INFO com.tinygao.thread.job.Job - FILE_JOB job status : STARTING， elapse time : 0s
2017-01-14 21:34:50.198 [main] INFO com.tinygao.thread.job.Job - FILE_JOB job status : RUNNING， elapse time : 0s
2017-01-14 21:34:51.200 [main] INFO com.tinygao.thread.job.Job - FILE_JOB job status : RUNNING， elapse time : 0s
2017-01-14 21:34:52.202 [main] INFO com.tinygao.thread.job.Job - FILE_JOB job status : RUNNING， elapse time : 1s
2017-01-14 21:34:53.204 [main] INFO com.tinygao.thread.job.Job - FILE_JOB job status : RUNNING， elapse time : 3s
2017-01-14 21:34:54.207 [main] INFO com.tinygao.thread.job.Job - FILE_JOB job status : RUNNING， elapse time : 4s
2017-01-14 21:34:55.208 [main] INFO com.tinygao.thread.job.Job - FILE_JOB job status : RUNNING， elapse time : 5s
2017-01-14 21:34:55.208 [main] INFO com.tinygao.thread.job.Job - FILE_JOB job status : FINISHED， elapse time : 5s
2017-01-14 21:34:55.208 [main] INFO com.tinygao.thread.ExecutionSingleClient - total elapse time 15s

2. 使用多线程情况

package com.tinygao.thread;

import com.google.common.base.Stopwatch;
import com.google.common.util.concurrent.ThreadFactoryBuilder;
import com.tinygao.thread.Execution;
import com.tinygao.thread.executor.JobExecutionFactory;
import com.tinygao.thread.job.DBJob;
import com.tinygao.thread.job.FileJob;
import com.tinygao.thread.job.Job;
import com.tinygao.thread.job.JobType;
import lombok.extern.slf4j.Slf4j;

import java.net.URI;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.TimeUnit;

import static java.util.concurrent.Executors.newFixedThreadPool;

/**
 * Created by gsd on 2017/1/14.
 */
@Slf4j
public class ExecutionMultiClient {

    public static ThreadFactory daemonThreadsNamed(String nameFormat){
        return new ThreadFactoryBuilder().setNameFormat(nameFormat).setDaemon(false).build();
    }

    public static void main(String[] args) throws Exception {
        final Stopwatch stopwatch = Stopwatch.createStarted();

        ExecutorService threads = Executors.newFixedThreadPool(
                    2,
                    daemonThreadsNamed("job-threads-%d"));
        threads.submit(ExecutionMultiClient::runDBJob);
        threads.submit(ExecutionMultiClient::runFileJob);

        threads.shutdown();
        threads.awaitTermination(1, TimeUnit.DAYS);

        log.info("total elapse time {}s", stopwatch.elapsed(TimeUnit.SECONDS));
        stopwatch.stop();
    }

    private static void runDBJob() {
        //创建一个任务
        Job dbJob = new DBJob("select * from tbl_user");
        //创建一个数据库执行者
        Execution dbExecution = new Execution(
                dbJob,
                JobExecutionFactory.createInstance(JobType.DB_JOB));
        try {
            dbExecution.call();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private static void runFileJob() {
        //创建一个任务
        try {
        Job fileJob = new FileJob(new URI("file://d:"));
        //创建一个文件执行者
        Execution fileExecution = new Execution(
                fileJob,
                JobExecutionFactory.createInstance(JobType.FILE_JOB));

            fileExecution.call();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

输出：

2017-01-14 21:38:13.384 [job-threads-1] INFO com.tinygao.thread.job.Job - FILE_JOB job status : STARTING， elapse time : 0s
2017-01-14 21:38:13.384 [job-threads-0] INFO com.tinygao.thread.job.Job - DB_JOB job status : STARTING， elapse time : 0s
2017-01-14 21:38:13.391 [job-threads-1] INFO com.tinygao.thread.job.Job - FILE_JOB job status : RUNNING， elapse time : 0s
2017-01-14 21:38:13.391 [job-threads-0] INFO com.tinygao.thread.job.Job - DB_JOB job status : RUNNING， elapse time : 0s
2017-01-14 21:38:14.404 [job-threads-1] INFO com.tinygao.thread.job.Job - FILE_JOB job status : RUNNING， elapse time : 1s
2017-01-14 21:38:14.405 [job-threads-0] INFO com.tinygao.thread.job.Job - DB_JOB job status : RUNNING， elapse time : 1s
2017-01-14 21:38:15.426 [job-threads-0] INFO com.tinygao.thread.job.Job - DB_JOB job status : RUNNING， elapse time : 2s
2017-01-14 21:38:15.426 [job-threads-1] INFO com.tinygao.thread.job.Job - FILE_JOB job status : RUNNING， elapse time : 2s
2017-01-14 21:38:16.427 [job-threads-1] INFO com.tinygao.thread.job.Job - FILE_JOB job status : RUNNING， elapse time : 3s
2017-01-14 21:38:16.427 [job-threads-0] INFO com.tinygao.thread.job.Job - DB_JOB job status : RUNNING， elapse time : 3s
2017-01-14 21:38:17.428 [job-threads-0] INFO com.tinygao.thread.job.Job - DB_JOB job status : RUNNING， elapse time : 4s
2017-01-14 21:38:17.428 [job-threads-1] INFO com.tinygao.thread.job.Job - FILE_JOB job status : RUNNING， elapse time : 4s
2017-01-14 21:38:18.429 [job-threads-1] INFO com.tinygao.thread.job.Job - FILE_JOB job status : RUNNING， elapse time : 5s
2017-01-14 21:38:18.429 [job-threads-0] INFO com.tinygao.thread.job.Job - DB_JOB job status : RUNNING， elapse time : 5s
2017-01-14 21:38:18.429 [job-threads-1] INFO com.tinygao.thread.job.Job - FILE_JOB job status : FINISHED， elapse time : 5s
2017-01-14 21:38:19.430 [job-threads-0] INFO com.tinygao.thread.job.Job - DB_JOB job status : RUNNING， elapse time : 6s
2017-01-14 21:38:20.430 [job-threads-0] INFO com.tinygao.thread.job.Job - DB_JOB job status : RUNNING， elapse time : 7s
2017-01-14 21:38:21.432 [job-threads-0] INFO com.tinygao.thread.job.Job - DB_JOB job status : RUNNING， elapse time : 8s
2017-01-14 21:38:22.434 [job-threads-0] INFO com.tinygao.thread.job.Job - DB_JOB job status : RUNNING， elapse time : 9s
2017-01-14 21:38:23.440 [job-threads-0] INFO com.tinygao.thread.job.Job - DB_JOB job status : RUNNING， elapse time : 10s
2017-01-14 21:38:23.440 [job-threads-0] INFO com.tinygao.thread.job.Job - DB_JOB job status : FINISHED， elapse time : 10s
2017-01-14 21:38:23.440 [main] INFO com.tinygao.thread.ExecutionMultiClient - total elapse time 10s

3. 分析

当cpu时间片轮到某一个线程时候，他就会执行它（如果可执行）
同一个应用在多线程和单线程情况下，多线程获取的cpu时间可能较多
从上面的例子可以看出多线程在较短的时间内完成两个任务。吞吐量高。

4. 总结

<b>from 《现代操作系统》p53</b>

许多应用中有多种活动，某些活动随着时间推移会被阻塞。通过将应用程序分解成可并行运行的多个线程来优化。
线程比进程更轻量级，比进程更快创建和撤销。在许多系统中，创建线程较创建进程要快10~100倍。
若多线程都是CPU密集型，性能上无法得以提升。如果存在大量计算和大量的I/O处理，拥有多线程允许这些活动彼此重叠进行，从而加快应用程序的执行速度。

5. 遗留问题

需要讲解阻塞（举例：cpu指令阻塞、应用层面的IO阻塞）

网友评论

本文标题：【为什么需要多线程】

本文链接：https://www.haomeiwen.com/subject/hvoebttx.html

延伸阅读

深度阅读

您也可以注册成为美文阅读网的作者，发表您的原创作品、分享您的心情！

【为什么需要多线程】

1. 没有使用多线程情况

2. 使用多线程情况

3. 分析

4. 总结

5. 遗留问题

相关文章

网友评论

延伸阅读

深度阅读

栏目导航

热点阅读