Basics.java

import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.ConcurrentHashMap;


public class Basics {
	public static void main(String[] args){
		new Basics().main();
	}

	public void main(){ /*{{{*/
		// 他スレッドから割り込みを受けないMap
		System.out.println("Take unsafe {{{");
		this.unsafe();
		System.out.println("}}}");

		System.out.println("Take safe {{{");
		this.safe();
		System.out.println("}}}");
	} /*}}}*/


	private ConcurrentMap<String,Integer> safeMap;
	public void unsafe(){ /*{{{*/
		this.safeMap = new ConcurrentHashMap<>();
		safeMap.put("a", 10);

		Runnable jamming0 = () -> {
			int sum = safeMap.get("a");
			for(int i=0; i<100; i++){
				sum += i;
				safeMap.replace("a", sum);
				System.out.println(i + ":" + safeMap.get("a"));
			}
		};

		Thread tx[] = {
			new Thread(jamming0),
			new Thread(jamming0)
		};
		for(Thread t : tx)
			t.start();

		try{
			tx[0].join();
			tx[1].join();
		}catch(InterruptedException e){
			e.printStackTrace();
		}
		int sum = 10;
		for(int i=0; i<200; i++, sum+=i);
		System.out.println("Is " + sum + " ?");
	} /*}}}*/
	public void safe(){ /*{{{*/
		this.safeMap = new ConcurrentHashMap<>();
		safeMap.put("a", 10);

		Runnable jamming0 = () -> {
			int sum = safeMap.get("a");
			for(int i=0; i<100; i++){
				sum += i;
				safeMap.putIfAbsent("a", sum);
				System.out.println(i + ":" + safeMap.get("a"));
			}
		};

		Thread tx[] = {
			new Thread(jamming0, "A"),
			new Thread(jamming0, "B")
		};
		for(Thread t : tx)
			t.start();

		try{
			tx[0].join();
			tx[1].join();
		}catch(InterruptedException e){
			e.printStackTrace();
		}
		int sum = 10;
		for(int i=0; i<200; i++, sum+=i);
		System.out.println("Is " + sum + " ?");
	} /*}}}*/
}