Simplify code in a few places (nits)

Author: sungshik

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

@@ -125,8 +125,8 @@ public static Closeable register(SubscriptionKey path, Consumer<List<WatchEvent<
         try {
             return CompletableFuture.supplyAsync(() -> {
                 try {
+                    Watchable watchable = Platform.get().newWatchable(path.getPath());
                     WatchEvent.Kind<?>[] kinds = new WatchEvent.Kind[]{ ENTRY_CREATE, ENTRY_MODIFY, OVERFLOW, ENTRY_DELETE };
-                    var watchable = Platform.get().newWatchable(path.getPath());
                     if (path.isRecursive()) {
                         return watchable.register(service, kinds, ExtendedWatchEventModifier.FILE_TREE);
                     }

src/main/java/engineering/swat/watch/impl/mac/MacWatchKey.java

@@ -50,10 +50,9 @@ public class MacWatchKey implements WatchKey {
     private final NativeEventStream stream;
 
     private volatile Configuration config = new Configuration();
-    private volatile boolean signalled = false;
+    private volatile boolean signalled = false; // `!signalled` means "ready"
     private volatile boolean cancelled = false;
 
-
     public MacWatchKey(MacWatchable watchable, MacWatchService service) throws IOException {
         this.watchable = watchable;
         this.service = service;
@@ -198,8 +197,10 @@ public boolean reset() {
             return false;
         }
 
-        signalled = false;
-        signalWhen(!pendingEvents.isEmpty());
+        if (signalled) {
+            signalled = false;
+            signalWhen(!pendingEvents.isEmpty());
+        }
 
         // Invalidation of this key *during* the invocation of this method is
         // observationally equivalent to invalidation immediately *after*. Thus,

src/main/java/engineering/swat/watch/impl/mac/MacWatchable.java

@@ -75,7 +75,7 @@ public WatchKey register(WatchService watcher, Kind<?>[] events, Modifier... mod
         var service = (MacWatchService) watcher;
         var newKey = new MacWatchKey(this, service);
         var oldKey = registrations.putIfAbsent(service, newKey);
-        return (oldKey == null ? newKey : oldKey).initialize(events, modifiers);
+        return (oldKey != null ? oldKey : newKey).initialize(events, modifiers);
     }
 
     @Override