"System Thread" is buggy

[laeubi]

Since a while some threads are marked as System Thread (maybe since Java 25?) in jdt debug view but the behave buggy:

1. Sometimes JDT stops on a breakpoint (jumping to editor location) but the thread does not gets selected like with "usual" threads and one has to find the thread to continue it or see the local variables.
2. Even worse, sometimes this thread vanished completely (or I'm unable to see it marked as paused) resulting in the JVM halts, but no way to continue it unless one selects the process itself and uses resume all. This even happens if the Thread was previously selected.

[iloveeclipse]

Any reproducible example? Can you please show which filters are enabled in debugger (Debug view menu -> Java -> ...), like here:

[laeubi]

Any reproducible example?

Not really, it suddenly appears that somehow (maybe the common pool?) some threads become a "System Thread" I have never noticed that before.

For me "Show System Threads" is disabled what then of course leads to the question why they are shown at all and how user code can execute in "System Threads" (whatever makes them "system").

[laeubi]

Okay I think I found a simple example that shows the SystemThreads:

package systemThreadTest;

import java.util.Arrays;

public class RunMe {

	public static void main(String[] args) {
		Arrays.stream(args).parallel().forEach(RunMe::debugMe);
	}

	private static void debugMe(String s) {
		System.out.println(s);
	}

}

but of course it seem to work with this simple example....

[trancexpress]

Hiding system threads likely means a filter is added to the view. My experience is that the filters break the view, highly likely due to concurrency problems.

Likely something breaks in the children updates, between the thread model and the indices of elements in the view, when filters are applied...

Update mechanism is listed here:

t/eclipse.jdt.core/wiki/JDT-Debug-View-update-mechanism

It was complicated enough to not try to fix also the filters, when we were looking into sporadic failures in our debug tests...