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#100 Added test case for demonstrating the thread safety issues of a

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naive lazy loaded Singleton implementation.
This commit is contained in:
Ilkka Seppala 2015-07-09 10:36:33 +03:00
parent db6ec3cc1a
commit 96241f63d2
1 changed files with 70 additions and 0 deletions
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singleton/src/test/java/com/iluwatar/singleton/LazyLoadedSingletonThreadSafetyTest.java Normal file
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package com.iluwatar.singleton;
import org.junit.Test;
/**
*
* This test case demonstrates thread safety issues of lazy loaded Singleton implementation.
*
* Out of the box you should see the test output something like the following:
*
* Thread=Thread-4 got instance=com.iluwatar.singleton.LazyLoadedSingletonThreadSafetyTest$LazyLoadedIvoryTower@6fde356e
* Thread=Thread-2 creating instance=com.iluwatar.singleton.LazyLoadedSingletonThreadSafetyTest$LazyLoadedIvoryTower@6fde356e
* Thread=Thread-0 creating instance=com.iluwatar.singleton.LazyLoadedSingletonThreadSafetyTest$LazyLoadedIvoryTower@6fde356e
* Thread=Thread-0 got instance=com.iluwatar.singleton.LazyLoadedSingletonThreadSafetyTest$LazyLoadedIvoryTower@6fde356e
* Thread=Thread-3 got instance=com.iluwatar.singleton.LazyLoadedSingletonThreadSafetyTest$LazyLoadedIvoryTower@6fde356e
* Thread=Thread-1 got instance=com.iluwatar.singleton.LazyLoadedSingletonThreadSafetyTest$LazyLoadedIvoryTower@60f330b0
* Thread=Thread-2 got instance=com.iluwatar.singleton.LazyLoadedSingletonThreadSafetyTest$LazyLoadedIvoryTower@6fde356e
*
* By changing the method signature of LazyLoadedIvoryTower#getInstance from
* public static LazyLoadedIvoryTower getInstance()
* into
* public synchronized static LazyLoadedIvoryTower getInstance()
* you should see the test output change to something like the following:
*
* Thread=Thread-4 creating instance=com.iluwatar.singleton.LazyLoadedSingletonThreadSafetyTest$LazyLoadedIvoryTower@3c688490
* Thread=Thread-4 got instance=com.iluwatar.singleton.LazyLoadedSingletonThreadSafetyTest$LazyLoadedIvoryTower@3c688490
* Thread=Thread-0 got instance=com.iluwatar.singleton.LazyLoadedSingletonThreadSafetyTest$LazyLoadedIvoryTower@3c688490
* Thread=Thread-3 got instance=com.iluwatar.singleton.LazyLoadedSingletonThreadSafetyTest$LazyLoadedIvoryTower@3c688490
* Thread=Thread-2 got instance=com.iluwatar.singleton.LazyLoadedSingletonThreadSafetyTest$LazyLoadedIvoryTower@3c688490
* Thread=Thread-1 got instance=com.iluwatar.singleton.LazyLoadedSingletonThreadSafetyTest$LazyLoadedIvoryTower@3c688490
*
*/
public class LazyLoadedSingletonThreadSafetyTest {
private static final int NUM_THREADS = 5;
@Test
public void test() {
SingletonThread runnable = new SingletonThread();
for (int j=0; j<NUM_THREADS; j++) {
Thread thread = new Thread(runnable);
thread.start();
}
}
private static class SingletonThread implements Runnable {
@Override
public void run() {
LazyLoadedIvoryTower instance = LazyLoadedIvoryTower.getInstance();
System.out.println("Thread=" + Thread.currentThread().getName() + " got instance=" + instance);
}
}
private static class LazyLoadedIvoryTower {
private static LazyLoadedIvoryTower instance = null;
private LazyLoadedIvoryTower() {
}
public static LazyLoadedIvoryTower getInstance() {
if (instance == null) {
instance = new LazyLoadedIvoryTower();
System.out.println("Thread=" + Thread.currentThread().getName() + " creating instance=" + instance);
}
return instance;
}
}
}