// Example 114 from page 87

//

import java.util.concurrent.Executors;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Future;

// C# example from Ostrovsky: The C# Memory Model in Theory and

// Practice, in MSDN Magazine, part 2 (January 2013); test harness by

// Jacob Thamsborg; Java version by [email protected] 2015-02-27

class Example114 {

public static void main(String[] args) throws Exception {

final ExecutorService executor = Executors.newWorkStealingPool();

final int numberOfAttempts = 1000000;

final int[][] wins = { { 0, 0 }, { 0, 0 } };

System.out.printf("Running %d experiments:%n", numberOfAttempts);

for (int count = 0; count < numberOfAttempts; count++) {

StoreBufferExample sharedState = new StoreBufferExample();

Future f1 = executor.submit(() -> { sharedState.ThreadA(); });

Future f2 = executor.submit(() -> { sharedState.ThreadB(); });

f1.get();

f2.get();

wins[sharedState.A_Won][sharedState.B_Won]++;

}

System.out.printf("No one won: %8d%n", wins[0][0]);

System.out.printf("A won: %8d%n", wins[1][0]);

System.out.printf("B won: %8d%n", wins[0][1]);

System.out.printf("Both (!) won: %8d%n", wins[1][1]);

}

}

class StoreBufferExample {

public /* volatile */ boolean A = false, B = false;

public int A_Won = 0, B_Won = 0;

public void ThreadA() {

A = true;

if (!B)

A_Won = 1;

}

public void ThreadB() {

B = true;

if (!A)

B_Won = 1;

}

}

// Results from Java 1.8.0_11 on Intel i7, with volatile:

// No one won: 2668

// A won: 438518

// B won: 558814

// Both (!) won: 0

// Results from Java 1.8.0_11 on Intel i7, without volatile:

// No one won: 0

// A won: 436649

// B won: 550463

// Both (!) won: 12888