JAVA同時制御のいくつかの方法

10枚の切符があれば、今3つの窓口(スレッド)で売る必要があります.コードは以下の通りです.
 
 

package com.test.runnable;

class MyThread implements Runnable {
	private int ticket = 10;
	public void run() {
		while (ticket > 0) {
			System.out.println("ticket = " + ticket--);
			try {
				Thread.sleep(2000l);
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
	}
}

public class RunnableDemo{
	public static void main(String[] args){
		MyThread my = new MyThread();
		new Thread(my).start();
		new Thread(my).start();
		new Thread(my).start();
	}
}

出力結果:
 
ticket = 10
ticket = 9
ticket = 8
ticket = 7
ticket = 7
ticket = 7
ticket = 6
ticket = 5
ticket = 6
ticket = 4
ticket = 4
ticket = 3
ticket = 2
ticket = 1
ticket = 2
10枚以上売れていることがわかりますので、同時制御を行います.
 
第1の方法は、同期キーを採用することです.
 

package com.test.runnable;

class MyThread implements Runnable {
	private int ticket = 10;
	synchronized public void run() {
		while (ticket > 0) {
			System.out.println("ticket = " + ticket--);
			try {
				Thread.sleep(2000);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	}
}

public class RunnableDemo{
	public static void main(String[] args){
		MyThread my = new MyThread();
		new Thread(my).start();
		new Thread(my).start();
		new Thread(my).start();
	}
}

出力結果は次のとおりです.
 
ticket = 10
ticket = 9
ticket = 8
ticket = 7
ticket = 6
ticket = 5
ticket = 4
ticket = 3
ticket = 2
ticket = 1
これで複数の窓口で切符を売ることができ、正確に、
 
2.原子変数を用いてもよい
 

package com.test.runnable;

import java.util.concurrent.atomic.AtomicInteger;

class MyThread implements Runnable {
	private AtomicInteger ticket = new AtomicInteger(10);
	synchronized public void run() {
		while (ticket.get() > 0) {
			System.out.println("ticket = " + ticket.getAndAdd(-1));
			try {
				Thread.sleep(2000);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	}
}

public class RunnableDemo{
	public static void main(String[] args){
		MyThread my = new MyThread();
		new Thread(my).start();
		new Thread(my).start();
		new Thread(my).start();
	}
}

3.信号量Semaphoreを採用

package com.test.runnable;

import java.util.concurrent.Semaphore;

class MyThread implements Runnable {
	final Semaphore semp = new Semaphore(1);
	private  int ticket = 10;
	public void run() {
		//  
        try {
			semp.acquire();
		} catch (InterruptedException e1) {
			// TODO Auto-generated catch block
			e1.printStackTrace();
		}
		while (ticket > 0) {
			System.out.println("ticket = " + ticket--);
			try {
				Thread.sleep(2000);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
		//  ， 
        semp.release();
	}
}

public class RunnableDemo{
	public static void main(String[] args){
		MyThread my = new MyThread();
		new Thread(my).start();
		new Thread(my).start();
		new Thread(my).start();
	}
}

 
 4.ロック採用

package com.test.runnable;

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

class MyThread implements Runnable {
	private Lock myLock = new ReentrantLock(); //  
	private  int ticket = 10;
	public void run() {
		myLock.lock();
		while (ticket > 0) {
			System.out.println("ticket = " + ticket--);
			try {
				Thread.sleep(2000);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
		//  ， 
		myLock.unlock();
	}
}

public class RunnableDemo{
	public static void main(String[] args){
		MyThread my = new MyThread();
		new Thread(my).start();
		new Thread(my).start();
		new Thread(my).start();
	}
}

 
5.スレッド内の変数の値が元の値に依存して更新されるため、volatileキーワードは使用できません.

package com.test.runnable;

class MyThread implements Runnable {
	//private volatile int ticket = 10;
	private volatile int ticket = 10;
	public void run() {
		while (ticket > 0) {
			System.out.println("ticket = " + ticket--);
			try {
				Thread.sleep(2000);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	}
}

public class RunnableDemo{
	public static void main(String[] args){
		MyThread my = new MyThread();
		new Thread(my).start();
		new Thread(my).start();
		new Thread(my).start();
	}
}