老谈synchronized,lock的区别及问题.

最新推荐文章于 2025-12-06 14:52:23 发布

原创最新推荐文章于 2025-12-06 14:52:23 发布 · 129 阅读

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#线程 #同步 #安全

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本文通过两个Java示例对比分析了synchronized与Lock的不同之处，包括它们的灵活性、等待机制及如何影响线程调度。

先看个代码吧!


import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class TestThread {
	public static long t=0;
	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO 自动生成方法存根

		TestThread2 tt = new TestThread2();
		System.out.println(t=System.currentTimeMillis());
		new Thread(tt).start();
		new Thread(tt).start();
		new Thread(tt).start();
		new Thread(tt).start();
		new Thread(tt).start();

	}
}

class TxtThread implements Runnable {
	int num = 100;
	String str = new String();

	public void run() {
		while (num > 0) {
			synchronized (str) {
				if (num > 0) {
					try {
						Thread.sleep(1000);
					} catch (Exception e) {
						e.getMessage();
					}
					System.out.println(Thread.currentThread().getName()
							+ "this is " + num--);
				}
			}
		}
	}
}

class TestThread2 implements Runnable {
	int num = 100;
	String str = new String();

	@Override
	public void run() {
		Lock lock=new ReentrantLock();
		while (num > 0) {
			lock.lock();
			try {
				boolean b=lock.tryLock(100,TimeUnit.MILLISECONDS);
				if (num > 0) {
					Thread.sleep(100);
				}
				if(num==0){
					return;
				}
				System.out.println(Thread.currentThread().getName()
						+ "this is " + num--);
			} catch (Exception e) {
				e.getMessage();
			}finally{
			lock.unlock();
			}
		}
		System.out.println("cost time is: "+(System.currentTimeMillis()-TestThread.t));
	}

}

synchronized的执行方式是:谁获得了锁,谁就执行,其他的线程都会处于等待状态,等当前线程执行完之后,根据系统的线程调用规则来调用数据.可以这样说吧,synchronized比较死板,不灵活,所以就要使用Lock锁来进行同步了! 上面的例子不是太清晰,再发个


package com.virusyang.tools;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class ThreadTest2 {

	/**
	 * @param args
	 */
	private static long c = 0;

	public static void main(String[] args) {
		final Lock l = new ReentrantLock();
		Thread t1 = new Thread() {
			public void run() {
				for (int i = 0; i < 10;) {
					try {
						if (l.tryLock()) {
							c++;
							i++;

							System.out.println(Thread.currentThread().getName()
									+ " t1 this is " +c);
							l.unlock();
						}
					} catch (Exception e) {
						// TODO Auto-generated catch block
						e.printStackTrace();
					}
				}
			}
		};
		Thread t2 = new Thread() {
			public void run() {
				for (int i = 0; i < 10;) {

						try {
							if (l.tryLock(250,TimeUnit.MILLISECONDS)) {
								c++;
								i++;
								System.out.println(Thread.currentThread().getName()
										+ " t2 this is " +c);
								l.unlock();
							}
						} catch (InterruptedException e) {
							// TODO Auto-generated catch block
							e.printStackTrace();
						}

				}
			}
		};
		long t = System.currentTimeMillis();
		Thread t3 = new Thread() {
			public void run() {
				for (int i = 0; i < 10;) {
					try {
						if (l.tryLock()) {
							c++;
							i++;

							System.out.println(Thread.currentThread().getName()
									+ " t3 this is " +c);
							l.unlock();
						}
					} catch (Exception e) {
						// TODO Auto-generated catch block
						e.printStackTrace();
					}
				}
			}
		};

		Thread t4 = new Thread() {
			public void run() {
				for (int i = 0; i < 10;) {
					try {
						if (l.tryLock()) {
							c++;
							i++;

							System.out.println(Thread.currentThread().getName()
									+ " t4 this is " +c);
							l.unlock();
						}
					} catch (Exception e) {
						// TODO Auto-generated catch block
						e.printStackTrace();
					}
				}
			}
		};


		t2.start();
		t1.start();
		t3.start();
		t4.start();

	}

}

这个例子执行的时候,分为lock(),trylock(),trylock(arg,arg)三种方法,其中使用第三种方法的时候线程的执行是独占的,trylock()是在系统空闲时就申请,不会等待,没有第三种方法灵活,lock()则和synchronized修饰的代码块差不多!

大家把例子运行下就能看出来差别,如有不对的地方欢迎大家拍砖.