java synchronized关键字用法

最新推荐文章于 2023-02-15 16:52:04 发布

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本文通过两个实验对比了在多线程环境下，不使用synchronized关键字和使用synchronized关键字对int型变量进行叠加操作的结果。实验结果显示，不使用synchronized关键字时，变量叠加可能出现数据不一致的问题；而使用synchronized关键字可以有效避免此类问题，确保数据的一致性和线程安全。

1.多线程处理一个int型变量的叠加，在不加锁的情况下会出现数据不一致的情况

package com.testsyn;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class Test {

	static int nmb = 0;

	public static void add() {
		nmb++;
	}

	public static void main(String args[]) {

		myRunnable mr = new myRunnable();
		ExecutorService exe = Executors.newFixedThreadPool(100);
		long time1 = System.currentTimeMillis();
		for (int i = 0; i < 1000; i++) {
			exe.execute(mr);
		}
		exe.shutdown();
		while (!exe.isTerminated()) {
			try {
				Thread.sleep(200);
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
		System.out.println("nmb:" + nmb + " costtime:" + (System.currentTimeMillis() - time1));
	}

	public static class myRunnable implements Runnable {

		@Override
		public void run() {
			// TODO Auto-generated method stub
			add();
		}

	}

}

执行结果

nmb:984 costtime:212

2.在函数上加synchronized关键字

package com.testsyn;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class Test {

	static int nmb = 0;

	public synchronized static void add() {
		nmb++;
	}

	public static void main(String args[]) {

		myRunnable mr = new myRunnable();
		ExecutorService exe = Executors.newFixedThreadPool(100);
		long time1 = System.currentTimeMillis();
		for (int i = 0; i < 1000; i++) {
			exe.execute(mr);
		}
		exe.shutdown();
		while (!exe.isTerminated()) {
			try {
				Thread.sleep(200);
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
		System.out.println("nmb:" + nmb + " costtime:" + (System.currentTimeMillis() - time1));
	}

	public static class myRunnable implements Runnable {

		@Override
		public void run() {
			// TODO Auto-generated method stub
			add();
		}

	}

}

执行结果

nmb:1000 costtime:211