多线程之Condition

 

 jdk 官网对Condition的描述：

Condition 将 Object 监视器方法（wait、notify 和 notifyAll）分解成截然不同的对象，以便通过将这些对象与任意 Lock 实现组合使用，为每个对象提供多个等待 set （wait-set）。其中，Lock 替代了 synchronized 方法和语句的使用，Condition 替代了 Object 监视器方法的使用。

 

下面通过网上一道面试题看看Condition的应用：

   启动三个线程，顺序打印ABC十次

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class PrintABC {
	Lock lock = new ReentrantLock();
	Condition aCdt = lock.newCondition();
	Condition bCdt = lock.newCondition();
	Condition cCdt = lock.newCondition();
	int order = 0;
	public static void main(String[] args) {
		final PrintABC print = new PrintABC();
		ExecutorService executorService = Executors.newFixedThreadPool(3);
		for (int i = 0; i < 10; i++) {
			executorService.execute(new Runnable() {
				@Override
				public void run() {
					print.printA();
				}
			});
			executorService.execute(new Runnable() {
				@Override
				public void run() {
					print.printB();
				}
			});
			executorService.execute(new Runnable() {
				@Override
				public void run() {
					print.printC();
				}
			});

		}
		executorService.shutdown();
	}

	public void printA() {
		try {
			lock.lock();
			while (order != 0) {
				aCdt.await();
			}
			System.out.println("A");
			order = 1;
			bCdt.signal();

		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} finally {
			lock.unlock();
		}
	}

	public void printB() {

		try {
			lock.lock();
			while (order != 1)
				bCdt.await();
			System.out.println("B");
			order = 2;
			cCdt.signal();

		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} finally {
			lock.unlock();
		}
	}

	public void printC() {

		try {
			lock.lock();
			while (order != 2)
				cCdt.await();
			System.out.println("C");
			order = 0;
			aCdt.signal();
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} finally {
			lock.unlock();
		}
	}

}