[jboss-dev-forums] [Design of Messaging on JBoss (Messaging/JBoss)] - An Exception handling case in threads

[gaohoward]

While working on https://jira.jboss.org/jira/browse/JBMESSAGING-1680, I need to create a thread and move some existing piece of code inside a method to that thread for concurrent execution. The method can be simplified as this:


  | public void methodA() throw Exception
  | {
  |    doWork1();
  |   
  |    doWork2();
  | }
  | 

doWork1() and doWork2() are two tasks independent of each other so they can be optimized using thread. So I plan to move doWork1() to another thread, like:


  | public void methodA() throw Exception
  | {
  |    new Thread() { public void run() { doWork1(); } }.start();
  | 
  |    doWork2();
  | }
  | 

The problems is that both doWork1() and doWork2() may throw Exception. So after my change, the doWork1() will be executed in a separate thread and it's exception will never be thrown from the calling thread of methodA(). To solve this, I uses a variable to hold the exception, like this:


  | public void methodA() throw Exception
  | {
  |    final ExceptionHolder holder = new ExceptionHolder(); //a holder simply holds an exception reference.
  | 
  |    new Thread() { public void run() { 
  |       try 
  |       {
  |          doWork1(); 
  |       }
  |       catch (Exception e)
  |       {
  |          holder = e; //pass the exception to holder.
  |       }
  |    } }.start();
  | 
  |    doWork2();
  | 
  |    //here using join() to wait for the thread finish and then
  |    if (holder.e != null)
  |    {
  |       throw holder.e;
  |    }
  | }
  | 

I don't know if this is the proper way. But that's my current solution.



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