Java并发编程实例--14.在一个同步类中安排独立属性

当你使用synchronized关键字去保护一个代码块时，你必须传入一个对象的引用。

正常来讲，你讲使用this关键字去引用执行这个方法的对象，但是你可以使用其他对象的引用。

通常的，这些对象将会是专有的。例如，如果多个线程共享一个类中有2个独立的属性，你必须对每个变量做读取同步操作，

但是如果一个线程读取一个属性而另一个线程读取另一个这个没问题的。

本例中，你讲学会如何解决这个问题。我们将模拟带有2块屏幕和2个售票窗口的电影院。

当一个售票窗口买票时，它卖出的肯定是其中某个播放厅的座位，这样一来每个厅的座位数就是独立的属性。

Cinema.java

package com.dylan.thread.ch2.c02.task;

public class Cinema {

	/**
	 * This two variables store the vacancies in two cinemas
	 */
	private long vacanciesCinema1;
	private long vacanciesCinema2;

	/**
	 * Two objects for the synchronization. ControlCinema1 synchronizes the
	 * access to the vacancesCinema1 attribute and controlCinema2 synchronizes
	 * the access to the vacanciesCinema2 attribute.
	 */
	private final Object controlCinema1, controlCinema2;

	/**
	 * Constructor of the class. Initializes the objects
	 */
	public Cinema(){
		controlCinema1=new Object();
		controlCinema2=new Object();
		vacanciesCinema1=20;
		vacanciesCinema2=20;
	}

	/**
	 * This method implements the operation of sell tickets for the cinema 1
	 * @param number number of tickets sold
	 * @return true if the tickets are sold, false if there is no vacancies
	 */
	public boolean sellTickets1 (int number) {
		synchronized (controlCinema1) {
			if (number<vacanciesCinema1) {
				vacanciesCinema1-=number;
				return true;
			} else {
				return false;
			}
		}
	}

	/**
	 * This method implements the operation of sell tickets for the cinema 2
	 * @param number number of tickets sold
	 * @return true if the tickets are sold, false if there is no vacancies
	 */
	public boolean sellTickets2 (int number){
		synchronized (controlCinema2) {
			if (number<vacanciesCinema2) {
				vacanciesCinema2-=number;
				return true;
			} else {
				return false;
			}
		}
	}

	/**
	 * This method implements the operation of return tickets for the cinema 1
	 * @param number number of the tickets returned
	 * @return true
	 */
	public boolean returnTickets1 (int number) {
		synchronized (controlCinema1) {
			vacanciesCinema1+=number;
			return true;
		}
	}

	/**
	 * This method implements the operation of return tickets for the cinema 1
	 * @param number number of the tickets returned
	 * @return true
	 */
	public boolean returnTickets2 (int number) {
		synchronized (controlCinema2) {
			vacanciesCinema2+=number;
			return true;
		}
	}

	/**
	 * Return the vacancies in the cinema 1
	 * @return the vacancies in the cinema 1
	 */
	public long getVacanciesCinema1() {
		return vacanciesCinema1;
	}

	/**
	 * Return the vacancies in the cinema 2
	 * @return the vacancies in the cinema 2
	 */
	public long getVacanciesCinema2() {
		return vacanciesCinema2;
	}

}

TicketOffice1.java

package com.dylan.thread.ch2.c02.task;

/**
 * This class simulates a ticket office. It sell or return tickets
 * for the two cinemas
 *
 */
public class TicketOffice1 implements Runnable {

	/**
	 * The cinema
	 */
	private Cinema cinema;

	/**
	 * Constructor of the class
	 * @param cinema the cinema
	 */
	public TicketOffice1 (Cinema cinema) {
		this.cinema=cinema;
	}

	/**
	 * Core method of this ticket office. Simulates selling and returning tickets
	 */
	@Override
	public void run() {
		cinema.sellTickets1(3);
		cinema.sellTickets1(2);
		cinema.sellTickets2(2);
		cinema.returnTickets1(3);
		cinema.sellTickets1(5);
		cinema.sellTickets2(2);
		cinema.sellTickets2(2);
		cinema.sellTickets2(2);
	}

}

TicketOffice2

package com.dylan.thread.ch2.c02.task;

/**
 * This class simulates a ticket office. It sell or return tickets
 * for the two cinemas
 *
 */
public class TicketOffice2 implements Runnable {

	/**
	 * The cinema
	 */
	private Cinema cinema;

	/**
	 * Constructor of the class
	 * @param cinema the cinema
	 */
	public TicketOffice2(Cinema cinema){
		this.cinema=cinema;
	}

	/**
	 * Core method of this ticket office. Simulates selling and returning tickets
	 */
	@Override
	public void run() {
		cinema.sellTickets2(2);
		cinema.sellTickets2(4);
		cinema.sellTickets1(2);
		cinema.sellTickets1(1);
		cinema.returnTickets2(2);
		cinema.sellTickets1(3);
		cinema.sellTickets2(2);
		cinema.sellTickets1(2);
	}

}

Main.java

package com.dylan.thread.ch2.c02.core;

import com.dylan.thread.ch2.c02.task.Cinema;
import com.dylan.thread.ch2.c02.task.TicketOffice1;
import com.dylan.thread.ch2.c02.task.TicketOffice2;

/**
 * Core class of the example. Creates a cinema and two threads for
 * the ticket office. Run the threads to analyze the results obtained
 *
 */
public class Main {

	/**
	 * Main method of the example
	 * @param args
	 */
	public static void main(String[] args) {
		// Creates a Cinema
		Cinema cinema=new Cinema();

		// Creates a TicketOffice1 and a Thread to run it
		TicketOffice1 ticketOffice1=new TicketOffice1(cinema);
		Thread thread1=new Thread(ticketOffice1,"TicketOffice1");

		// Creates a TicketOffice2 and a Thread to run it
		TicketOffice2 ticketOffice2=new TicketOffice2(cinema);
		Thread thread2=new Thread(ticketOffice2,"TicketOffice2");

		// Starts the threads
		thread1.start();
		thread2.start();

		try {
			// Waits for the finalization of the threads
			thread1.join();
			thread2.join();
		} catch (InterruptedException e) {
			e.printStackTrace();
		}

		// Print the vacancies in the cinemas
		System.out.printf("Room 1 Vacancies: %d\n",cinema.getVacanciesCinema1());
		System.out.printf("Room 2 Vacancies: %d\n",cinema.getVacanciesCinema2());
	}

}

运行结果：

Room 1 Vacancies: 5
Room 2 Vacancies: 6