The threadpool executer in ThreadUtil prevents the JVM from exiting.

[odinsbane]

When tasks are called that use the ThreadUtil.threadPoolExecutor the executor prevents the jvm from exiting after the task/program has finished.

For example:

import ij.process.ImageProcessor;
import ij.process.ShortProcessor;
import ij.util.ThreadUtil;

public class HoldUp {

    public static void main(String[] args){
        ImageProcessor proc = new ShortProcessor(256, 256);
        proc.blurGaussian( 2.0 );
        //ThreadUtil.threadPoolExecutor.shutdown();
    }
}

That program will not finish unless the last line is uncommented. Some suggestions.

• Use ForkJoinPool.commonPool() it will have similar behavior but you dont have to shut it down.
• Use ExecutorService.invokeAll

[sabashaikh4]

Hello, I need permission to create a Pull Request for the implemented changes. Please grant access.

[ctrueden]

@sabashaikh4 I see you filed the PR (#291). I did a quick review. Have you tested that everything compiles successfully with Java 26? Have you tried dropping the resultant ij.jar into a Fiji installation to make sure it still works?

[sabashaikh4]

Thank you for reviewing the PR!

Regarding your questions:

1. Java 26 testing: Java 26 has not been released yet.
   I have tested the changes with Java 23, and
   the code compiles successfully. These changes are designed to be compatible
   with Java 26 by removing the deprecated Applet API before it's removed in
   that release.

2. Fiji testing: I have not yet tested the changes in a Fiji installation.
   I can do this testing if you'd like, or if you could guide me on the proper
   testing procedure for Fiji, I'd be happy to verify everything works correctly.

The changes made are:

• Replaced Applet type with Object
• Deprecated getApplet() to always return null
• Added setApplet() that throws UnsupportedOperationException if non-null
• Removed Applet-specific code from JavaProperties

These changes maintain backward compatibility while preparing for Java 26.
Please let me know if you'd like me to perform additional testing.

[ctrueden]

Ahh, I just realized I commented on the wrong issue. The correct issue regarding applet removal is #287, and like I linked above, the PR attempting to address it is #291. Neither is relevant to this issue here about thread management.