Java多线程18：公平锁与非公平锁

前言

公平锁与非公平锁：锁Lock分为“公平锁”和“非公平锁”，公平锁表示线程获取锁的顺序是按照线程加锁的顺序来分配的，即先来先得的FIFO先进先出顺序。而非公平锁就是一种获取锁的抢占机制，是随机获取锁的，和公平锁不一样的就是先来的不一定先得到锁，这个方式可能造成某些线程一直拿不到锁，结果也就是不公平得了。

创建公平锁

package unit3;

import java.util.concurrent.locks.ReentrantLock;

/**
 * 公平锁
 * @author Administrator
 *
 */

public class Demo9_Run {
	public static void main(String[] args) {
		//公平锁
		final Demo9Service service = new Demo9Service(true);
		//非公平锁
		//final Demo9Service service = new Demo9Service(false);
		Runnable runnalbe = new Runnable() {

			@Override
			public void run() {
				System.out.println("#线程" + Thread.currentThread().getName() + "运行了");
				service.serviceMethod();
				
			}
			
		};
		Thread[] threadArray = new Thread[20];
		for (int i = 0; i < 20; i++) {
			threadArray[i] = new Thread(runnalbe);
		}
		
		for (int i = 0; i < 20; i++) {
			threadArray[i].start();
		}
	}
}

class Demo9Service {
	private ReentrantLock lock;
	public Demo9Service(boolean isFair) {
		super();
		lock = new ReentrantLock(isFair);
	}
	
	public void serviceMethod() {
		try {
			lock.lock();
			System.out.println("ThreadName=" + 
			Thread.currentThread().getName() + "获得锁");
			
		} finally {
			lock.unlock();
		}
	}
}

创建非公平锁

package unit3;

import java.util.concurrent.locks.ReentrantLock;

/**
 * 公平锁
 * @author Administrator
 *
 */

public class Demo9_Run {
	public static void main(String[] args) {
		//公平锁
		//final Demo9Service service = new Demo9Service(true);
		//非公平锁
		final Demo9Service service = new Demo9Service(false);
		Runnable runnalbe = new Runnable() {

			@Override
			public void run() {
				System.out.println("#线程" + Thread.currentThread().getName() + "运行了");
				service.serviceMethod();
				
			}
			
		};
		Thread[] threadArray = new Thread[20];
		for (int i = 0; i < 20; i++) {
			threadArray[i] = new Thread(runnalbe);
		}
		
		for (int i = 0; i < 20; i++) {
			threadArray[i].start();
		}
	}
}

class Demo9Service {
	private ReentrantLock lock;
	public Demo9Service(boolean isFair) {
		super();
		lock = new ReentrantLock(isFair);
	}
	
	public void serviceMethod() {
		try {
			lock.lock();
			System.out.println("ThreadName=" + 
			Thread.currentThread().getName() + "获得锁");
			
		} finally {
			lock.unlock();
		}
	}
}