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.