How Get Inactive Threads of a ThreadGroup?

[Robert Paris]

ThreadGroup has a way to get all active threads of that thread group (enumerate). I can also get a list of the names of all active AND inactive threads (list). Does anyone know how I can actually get a reference to the inactive threads?
With enumerate, I can get actual references to the thread objects:
<ThreadGroup>.enumerate(Thread[] list, boolean recurse);
And I know the ThreadGroup has a reference to the inactive threads as well, because list will show the inactive threads too:
<ThreadGroup>.list();
Thanks!

[Robert Paris]

anyone? I can't find the answer anywhere, but really need to be able to do this! help!

[Robert Paris]

OK, here's how you do it:

 
/*
 * For testing purposes */
ThreadGroup tg = new ThreadGroup( "MyThreadGroup" );
Thread subThread = new Thread( tg, "New Thread - Inactive" );
try
{
/*
* GETTING THREADS - PROBABLY BETTER TO GET IT BY USING
* getDeclaredFields() AND LOOPING TILL GET ONE OF TYPE
* Thread[] SINCE A FUTURE VERSION MIGHT CHANGE THE NAME
* BUT SINCE IS PACKAGE-LEVEL ACCESS, IT'S PROBABLY USED
* ELSEWHERE IN THE PACKAGE, AND THIS IS JUST AN EXAMPLE
*/
Field field = tg.getClass().getDeclaredField( "threads" );

//NEED TO SUPPRESS ACCESS CHECKS
field.setAccessible( true ); //EVEN IF SECURITY IS OFF YOU NEED THIS!!!!

Thread[] tgThreads = ( Thread[] ) field.get( tg );

for ( int i = 0; i < tgThreads.length; i++ )
{
if ( tgThreads[ i ] != null )
System.out.println( tgThreads[ i ].getName() + " = " + tgThreads[ i ].isAlive() );
}
}
catch (NoSuchFieldException nsfe)
{
nsfe.printStackTrace();
}
catch (IllegalAccessException iae)
{
iae.printStackTrace();
}

A couple things:
1. You need to set the field accessible even without a security manager
2. If you have security on, you'll need the runtime permission "suppressAccessChecks" even though I know most people run with no security or "AllPermission".
3. That check for null is important! I believe it keeps more room than it needs, so it doesn't have to expand all the time, so you don't want to hit a null pointer.
Have fun!

[Cindy Glass]

Great! Now I think that I will move this to the Threads forum .