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  1. import java.util.*;
  2. import java.util.concurrent.locks.*;
  3.  
  4. class Locker implements AutoCloseable {
  5.     private final Lock lock;
  6.     Locker(Lock lock) { this.lock = Objects.requireNonNull(lock);
  7.                         this.lock.lock(); }
  8.     @Override public void close() { lock.unlock(); }
  9. }
  10.  
  11. class Example {
  12. 	static ReentrantLock lock = new ReentrantLock();
  13.     static void modifySharedState() {
  14.     	lock.unlock();              // program bug 1. causes unlock() in close() to throw
  15.     	((Object) null).toString(); // program bug 2. causes modifySharedState() to throw
  16.     }
  17.  
  18. 	public static void main(String[] args) {
  19. 		try (Locker locker = new Locker(lock)) {
  20. 		    // If both modifySharedState() and unlock()
  21. 		    // throw an exception, the unlock() exception
  22. 		    // is added to the modifySharedState()'s
  23. 		    // suppressed exceptions.
  24. 		    modifySharedState();
  25. 		}
  26. 	}
  27.  
  28. 	static {
  29. 		Thread.currentThread().setUncaughtExceptionHandler(
  30. 			(Thread t, Throwable x) ->
  31. 				x.printStackTrace(System.out)
  32. 		);
  33. 	}
  34. }
Runtime error #stdin #stdout 0.13s 4386816KB
comments (?)
stdin 
Standard input is empty
stdout 
java.lang.NullPointerException
	at Example.modifySharedState(Main.java:15)
	at Example.main(Main.java:24)
	Suppressed: java.lang.IllegalMonitorStateException
		at java.util.concurrent.locks.ReentrantLock$Sync.tryRelease(ReentrantLock.java:151)
		at java.util.concurrent.locks.AbstractQueuedSynchronizer.release(AbstractQueuedSynchronizer.java:1261)
		at java.util.concurrent.locks.ReentrantLock.unlock(ReentrantLock.java:457)
		at Locker.close(Main.java:8)
		at Example.main(Main.java:25)
https://ideone.com/f0zkYk
language:
Java (HotSpot 12)
created:
8 years ago
visibility:
public

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