Java并发学习之九——使用本地线程变量

灰太狼 2022-08-11 08:00 55阅读 0赞

本文是学习网络上的文章时的总结，感谢大家无私的分享。

1、如果创建一个类对象，实现Runnable接口，然后多个Thread对象使用同样的Runnable对象，全部的线程都共享同样的属性。这意味着，如果你在一个线程里改变一个属性，全部的线程都会受到这个改变的影响。如果希望程序里的哥哥线程的属性不会被共享，Java并发API提供了一个很清楚的机制叫本地线程变量。

2、Java并发API包括Inheritable ThreadLocal类提供线程创建线程的值的遗传性。如果线程A有一个本地线程变量，然后它创建了另一个线程B，那么线程B将有与A相同的本地线程变量值。你可以覆盖childValue方法来初始子线程的本地线程变量的值。它接收付线程的本地线程变量作为参数。

下面先介绍一个不使用本地线程变量的代码

package chapter;
    
    import java.util.Date;
    import java.util.concurrent.TimeUnit;
    
    public class UnsafeTask implements Runnable{
    	private Date startDate;
    	@Override
    	public void run() {
    		startDate = new Date();
    		System.out.printf("Starting Thread :%s:%s\n", Thread.currentThread().getId(),startDate);
    		
    		try {
    			TimeUnit.SECONDS.sleep((int)Math.rint(Math.random()*10));
    		} catch (InterruptedException e) {
    			e.printStackTrace();
    		}
    		System.out.printf("Thread Finished:%s:%s\n", Thread.currentThread().getId(),startDate);
    	}
    
    }

package chapter;
    
    import java.util.concurrent.TimeUnit;
    
    public class Main9 {
    
    	/**
    	 * <p>
    	 * </p>
    	 * @author zhangjunshuai
    	 * @date 2014-8-22 下午4:30:20
    	 * @param args
    	 */
    	public static void main(String[] args) {
    
    		UnsafeTask task = new UnsafeTask();
    		for(int i = 0; i<10;i++){
    			Thread thread = new Thread(task);
    			thread.start();
    			
    			try {
    				TimeUnit.SECONDS.sleep(2);
    			} catch (InterruptedException e) {
    				// TODO Auto-generated catch block
    				e.printStackTrace();
    			}
    		}
    		
    		/*SafeTask task = new SafeTask();
    		for(int i = 0; i<10;i++){
    			Thread thread = new Thread(task);
    			thread.start();
    			
    			try {
    				TimeUnit.SECONDS.sleep(2);
    			} catch (InterruptedException e) {
    				// TODO Auto-generated catch block
    				e.printStackTrace();
    			}
    		}*/
    	}
    
    }

![SouthEast][]

使用本地线程变量

package chapter;
    
    import java.util.Date;
    import java.util.concurrent.TimeUnit;
    
    public class SafeTask implements Runnable{
    
    	private static ThreadLocal<Date> startDate = new ThreadLocal<Date>(){
    		protected Date initialValue(){
    			return new Date();
    		}
    	};
    	@Override
    	public void run() {
    
    		System.out.printf("Starting Thread:%s:%s\n", Thread.currentThread().getId(),startDate.get()
    				);
    		 try {
    			TimeUnit.SECONDS.sleep((int)Math.rint(Math.random()*10));
    		} catch (InterruptedException e) {
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		}
    		 
    		 System.out.printf("Thread Finished:%s:%s\n", Thread.currentThread().getId(),startDate.get());
    	}
    }

package chapter;
    
    import java.util.concurrent.TimeUnit;
    
    public class Main9 {
    
    	/**
    	 * <p>
    	 * </p>
    	 * @author zhangjunshuai
    	 * @date 2014-8-22 下午4:30:20
    	 * @param args
    	 */
    	public static void main(String[] args) {
    
    		/*UnsafeTask task = new UnsafeTask();
    		for(int i = 0; i<10;i++){
    			Thread thread = new Thread(task);
    			thread.start();
    			
    			try {
    				TimeUnit.SECONDS.sleep(2);
    			} catch (InterruptedException e) {
    				// TODO Auto-generated catch block
    				e.printStackTrace();
    			}
    		}*/
    		
    		SafeTask task = new SafeTask();
    		for(int i = 0; i<10;i++){
    			Thread thread = new Thread(task);
    			thread.start();
    			
    			try {
    				TimeUnit.SECONDS.sleep(2);
    			} catch (InterruptedException e) {
    				// TODO Auto-generated catch block
    				e.printStackTrace();
    			}
    		}
    	}
    
    }

![SouthEast 1][]

[SouthEast]: /images/20220810/d753b17d90444a2081fb84a08606d9c8.png
[SouthEast 1]: /images/20220810/392ff0e56a0449c4a68e97a51a800a84.png