Question

I need some help concerning deadlocks. I just do not understand why my code is deadlocking here.

I tried different scenarios.

However I still can’t find why and where is the problem. Normally it should work
and I don’t find where the deadlock is between debuter and termine.

  public class Interblocking {
           protected object obj = object();
           private boolean condition = true;

           public synchronized void debuter() {
               synchronized(obj) {
                   while (!condition) {
                       try {
                           obj.wait();
                       } catch (InterruptedExeption ie) {}
                   }
                   condition = false;
               }
           }

           public synchronized void terminer() {
               synchronized(obj) {
                   condition = true;
                   obj.notifyAll();
               }
           }
        }

Answer 1

Edit (new answer)

Method wait() doesn’t release all locks of current Thread.

So when A thread invokes debuter it releases only obj lock but holds this lock so other threads can’t invoke terminer method.

Here is example:

class WaitReleaseTest implements Runnable {
    Object lockA, lockB;
    public WaitReleaseTest(Object lockA, Object lockB) {
        this.lockA = lockA;
        this.lockB = lockB;
    }

    public void run() {
        System.out.println(Thread.currentThread().getName()
                + " attempting to acquire lockA");
        synchronized (lockA) {
            System.out.println(Thread.currentThread().getName()
                    + " attempting to acquire lockB");
            synchronized (lockB) {
                System.out.println(Thread.currentThread().getName()
                        + " holds lockA = " + Thread.holdsLock(lockA));
                System.out.println(Thread.currentThread().getName()
                        + " holds lockB = " + Thread.holdsLock(lockB));
                try {
                    lockB.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    public static void main(String[] args) throws InterruptedException {
        Object o1=new Object();
        Object o2=new Object();
        new Thread(new WaitReleaseTest(o1,o2)).start();
        TimeUnit.MILLISECONDS.sleep(500);
        new Thread(new WaitReleaseTest(o1,o2)).start();
    }
}

output

Thread-0 attempting to acquire lockA
Thread-0 attempting to acquire lockB
Thread-0 holds lockA = true
Thread-0 holds lockB = true
Thread-1 attempting to acquire lockA
... now it waits