Question

I have a class called communicator. This class is a listener of a thread receiving events from another program. Also this class has a method call refresh that sends and action to the program a waits for the response that comes through the listener.

Both methods are in the same class but called by diferent threads.

public void processRefreshEvent(ManagerEvent event){     //processing event     //...     //I'm done     notify(); }   public synchronized void refresh() throws Exception {     isRefreshing = true;         try {                     manager.send(new refresh());     } catch (ManagerException e) {         isRefreshing = false;     }      try {             wait(5000);     } catch (InterruptedException e) {     } finally{         isRefreshing = false;     } } 

when executing the code above I get the follow exception:

java.lang.IllegalMonitorStateException: current thread not owner         at java.lang.Object.wait(Native Method)         at Communicator.refresh(Communicator.java:203)         ... 

What is the proper way to ‘wait’ for another thread to finish. Thanks.

Answer 1

You need to synchronize your threads on a monitor. For instance (using the current object as the monitor):

public void processRefreshEvent(ManagerEvent event){         //processing event         //...         //I'm done     synchronized(this) {         notify(); // you are basically notifying any thread who has blocked                   // on this monitor - in our case, the instance of this object     } }   public synchronized void refresh() throws Exception {         isRefreshing = true;             try {                     manager.send(new refresh());         } catch (ManagerException e) {                 isRefreshing = false;         }          try {           synchronized(this) {                 wait(5000); // wait will give up the monitor           }         } catch (InterruptedException e) {         } finally{                 isRefreshing = false;         } }