Java Wait and Notify: IllegalMonitorStateException

by

You can’t wait() on an object unless the current thread owns that object’s monitor. To do that, you must synchronize on it:

class Runner implements Runnable
{
  public void run()
  {
    try
    {
      synchronized(Main.main) {
        Main.main.wait();
      }
    } catch (InterruptedException e) {}
    System.out.println("Runner away!");
  }
}

The same rule applies to notify()/notifyAll() as well.

The Javadocs for wait() mention this:

This method should only be called by a thread that is the owner of this object’s monitor. See the notify method for a description of the ways in which a thread can become the owner of a monitor.

Throws:

IllegalMonitorStateException – if the current thread is not the owner of this object’s monitor.

And from notify():

A thread becomes the owner of the object’s monitor in one of three
ways:

  • By executing a synchronized instance method of that object.
  • By executing the body of a synchronized statement that synchronizes on the object.
  • For objects of type Class, by executing a synchronized static method of that class.

More Related Contents:

  1. How to wait for all threads to finish, using ExecutorService?
  2. Is there an advantage to use a Synchronized Method instead of a Synchronized Block?
  3. Why must wait() always be in synchronized block
  4. When and how should I use a ThreadLocal variable?
  5. What is the difference between Thread.start() and Thread.run()?
  6. Volatile vs Static in Java
  7. Are static variables shared between threads?
  8. How do synchronized static methods work in Java and can I use it for loading Hibernate entities?
  9. Why use a ReentrantLock if one can use synchronized(this)?
  10. Java Executors: how can I set task priority?
  11. Volatile variable in Java
  12. What is the JVM thread scheduling algorithm?
  13. How do I implement task prioritization using an ExecutorService in Java 5?
  14. Why does Thread.isInterrupted () always return false?
  15. Constructor synchronization in Java
  16. More efficient way for pausing loop wanted
  17. How does `this` reference to an outer class escape through publishing inner class instance?
  18. Javafx: Difference between javafx.concurent and Platform.runLater?
  19. Are non-synchronised static methods thread safe if they don’t modify static class variables?
  20. Instruction reordering & happens-before relationship [duplicate]
  21. Which concurrent Queue implementation should I use in Java?
  22. Why should I use concurrent characteristic in parallel stream with collect?
  23. Jboss Java EE container and an ExecutorService
  24. Why doesn’t volatile in java 5+ ensure visibility from another thread?
  25. How to pause/resume all threads in an ExecutorService in Java?
  26. Handling Exceptions for ThreadPoolExecutor
  27. Multithreading Socket communication Client/Server
  28. notifyAll() throws IllegalMonitorStateException
  29. Will a chain of method calls (CompletableFuture API) execute asynchronously if the first method in a chain is asynchronous?
  30. ExecutorCompletionService? Why do need one if we have invokeAll?

Leave a Comment