Question: Uncaught Exceptions in GIJ

[Andrew Haley]

Kyle Galloway writes:

 > I have a question about GIJ.  I was wondering how/where GIJ decides that 
 > an exception is unhandled (i.e. that nowhere along the call stack the 
 > exception was caught).

In fact *every* exception is caught by a global catch-all handler in
the outermost frame.  Here:


void
_Jv_ThreadRun (java::lang::Thread* thread)
{
  try
    {
      _Jv_NotifyThreadStart (thread);
      thread->run ();
    }
  catch (java::lang::Throwable *t)
    {
      // Uncaught exceptions are forwarded to the ThreadGroup.  If
      // this results in an uncaught exception, that is ignored.
      try
	{
	  thread->group->uncaughtException (thread, t);
	}
      catch (java::lang::Throwable *f)
	{
	  // Nothing.
	}
    }

  thread->finish_ ();
}


and here:

  /**
   * When a Thread in this ThreadGroup does not catch an exception, the
   * virtual machine calls this method. The default implementation simply
   * passes the call to the parent; then in top ThreadGroup, it will
   * ignore ThreadDeath and print the stack trace of any other throwable.
   * Override this method if you want to handle the exception in a different
   * manner.
   *
   * @param thread the thread that exited
   * @param t the uncaught throwable
   * @throws NullPointerException if t is null
   * @see ThreadDeath
   * @see System#err
   * @see Throwable#printStackTrace()
   */
  public void uncaughtException(Thread thread, Throwable t)
  {

...

Andrew.