Switch to an internal daemon threads based executor that also closes threads when not used that much

Author: DavyLandman

src/main/java/engineering/swat/watch/impl/jdk/JDKPoller.java

@@ -46,7 +46,11 @@
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
+import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.ThreadFactory;
+import java.util.concurrent.ThreadPoolExecutor;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
 import java.util.function.Consumer;
 
 import org.apache.logging.log4j.Level;
@@ -67,12 +71,23 @@ private JDKPoller() {}
     private static final Logger logger = LogManager.getLogger();
     private static final Map<WatchKey, Consumer<List<WatchEvent<?>>>> watchers = new ConcurrentHashMap<>();
     private static final WatchService service;
-    private static final int nCores = Runtime.getRuntime().availableProcessors();
     /**
      * We have to be a bit careful with registering too many paths in parallel
      * Linux can be thrown into a deadlock if you try to start 1000 threads and then do a register at the same time.
      */
-    private static final ExecutorService registerPool = Executors.newFixedThreadPool(nCores);
+    private static final ExecutorService registerPool = new ThreadPoolExecutor(
+            0, Runtime.getRuntime().availableProcessors(),
+            10, TimeUnit.SECONDS,
+            new LinkedBlockingQueue<>(), new ThreadFactory() {
+                private final AtomicInteger id = new AtomicInteger(0);
+                private final ThreadGroup group = new ThreadGroup("registry pool");
+                @Override
+                public Thread newThread(Runnable r) {
+                    var t = new Thread(group, r, "JavaWatch-registry-pool-" + id.incrementAndGet());
+                    t.setDaemon(true);
+                    return t;
+                }
+            });
 
     static {
         try {