互联网并发编程之一线程安全03线程中的脏读

本文通过一个具体的Java示例展示了线程同步的重要性。在多线程环境下，如果不使用同步机制，可能会导致数据读取错误（脏读）。通过给方法添加synchronized关键字可以确保线程安全。

当一个线程运行修改数据的方法，另一个线程启动读取数据的值，会读到未修改的前的数据

package com.jc.thread;

public class Thread04 {

	private String name = "abc";
	private String password = "123";

	public synchronized void setValue(String name, String password) {
		
		try {
			Thread.sleep(2000);
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		this.name = name;
		this.password = password;
	}

	public void getValue() {
		System.out.println(this.name);
		System.out.println(this.password);
	}

	public static void main(String[] args) {

		final Thread04 thread04 = new Thread04();
		Thread t1 = new Thread(new Runnable() {

			@Override
			public void run() {
				
				thread04.setValue("jkl", "333");
			}
		}, "t1");
		t1.start();
		try {
			Thread.sleep(1000);
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		thread04.getValue();
	}

}

输出结果为：

abc
123

对于对象的同步或者异步方法，我们在设计程序的时候一定要考虑整体性，不然会出现不一致的问题，很经典的错误就是脏读，当setValue()和getValue()同时加上synchronized 关键字，保证了业务的原子性。

package com.jc.thread;

public class Thread04 {

private String name = "abc";
private String password = "123";

public synchronized void setValue(String name, String password) {

try {
Thread.sleep(2000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
this.name = name;
this.password = password;
}

public synchronized void getValue() {
System.out.println(this.name);
System.out.println(this.password);
}

public static void main(String[] args) {

final Thread04 thread04 = new Thread04();
Thread t1 = new Thread(new Runnable() {

@Override
public void run() {

thread04.setValue("jkl", "333");
}
}, "t1");
t1.start();
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
thread04.getValue();
}

}