Fix Timer units and make setInterval repeat

The menu script passes intervals in milliseconds, but the Timer treated
them as seconds, so wait_then_call(1100, open_mm) waited 1100 seconds and
the menu never opened. setInterval also only fired once instead of
repeating, so the button 'arrive' animation never advanced. Both are fixed,
with a single scheduler thread serializing callbacks.

core/src/main/java/dev/quoije/umd/rco/vsmx/objects/Timer.java

@@ -11,17 +11,41 @@ import dev.quoije.umd.rco.vsmx.interpreter.VsmxNumber;
 import java.util.HashMap;
 import java.util.Map;
 
-/** The Timer native object: setTimeout-style intervals for menu animations. */
+/** The Timer native object: recurring setInterval callbacks for menu animations. */
 public class Timer extends BaseNativeObject {
 
     private final VsmxInterpreter interpreter;
+    private final Object callbackLock = new Object();
+    private final Map<Integer, Task> timers = new HashMap<>();
     private int currentTimerId;
-    private final Map<Integer, Thread> timers = new HashMap<>();
+
+    /** One recurring timer task. */
+    private static final class Task {
+        final VsmxBaseObject object;
+        final VsmxBaseObject function;
+        final VsmxBaseObject[] params;
+        final long intervalNanos;
+        long nextRunNanos;
+        boolean active = true;
+
+        Task(VsmxBaseObject object, VsmxBaseObject function, VsmxBaseObject[] params, long intervalNanos, long nextRunNanos) {
+            this.object = object;
+            this.function = function;
+            this.params = params;
+            this.intervalNanos = intervalNanos;
+            this.nextRunNanos = nextRunNanos;
+        }
+    }
 
     public static VsmxNativeObject create(VsmxInterpreter interpreter) {
         Timer timer = new Timer(interpreter);
         VsmxNativeObject object = new VsmxNativeObject(interpreter, timer);
         timer.setObject(object);
+
+        Thread scheduler = new Thread(timer::run, "umd-timer");
+        scheduler.setDaemon(true);
+        scheduler.start();
+
         return object;
     }
 
@@ -29,24 +53,52 @@ public class Timer extends BaseNativeObject {
         this.interpreter = interpreter;
     }
 
-    private VsmxBaseObject setInterval(VsmxBaseObject object, VsmxBaseObject function, VsmxBaseObject interval,
-                                       VsmxBaseObject... parameters) {
-        int id = currentTimerId++;
-        long millis = interval.getIntValue() * 1000L;
-        VsmxBaseObject[] params = parameters;
-        Thread thread = new Thread(() -> {
+    /** Single scheduler thread: fires due timers, serialized so the interpreter is never re-entered. */
+    private void run() {
+        while (true) {
+            Task due = null;
+            long waitNanos = 50_000_000L; // 50ms default idle poll
+            synchronized (timers) {
+                long now = System.nanoTime();
+                for (Task task : timers.values()) {
+                    if (!task.active) {
+                        continue;
+                    }
+                    if (task.nextRunNanos <= now) {
+                        task.nextRunNanos = now + task.intervalNanos;
+                        due = task;
+                        break;
+                    }
+                    waitNanos = java.lang.Math.min(waitNanos, task.nextRunNanos - now);
+                }
+            }
+
+            if (due != null) {
+                if (due.function instanceof VsmxFunction f) {
+                    synchronized (callbackLock) {
+                        interpreter.interpretFunction(f, due.object, due.params);
+                    }
+                }
+                continue;
+            }
+
             try {
-                Thread.sleep(millis);
+                Thread.sleep(waitNanos / 1_000_000L, (int) (waitNanos % 1_000_000L));
             } catch (InterruptedException e) {
                 return;
             }
-            if (function instanceof VsmxFunction f) {
-                interpreter.interpretFunction(f, object, params);
         }
-        }, "umd-timer-" + id);
-        thread.setDaemon(true);
-        timers.put(id, thread);
-        thread.start();
+    }
+
+    private VsmxBaseObject setInterval(VsmxBaseObject object, VsmxBaseObject function, VsmxBaseObject interval,
+                                       VsmxBaseObject... parameters) {
+        int id = currentTimerId++;
+        // The interval is expressed in milliseconds by the menu script.
+        long intervalNanos = java.lang.Math.max(1L, interval.getIntValue()) * 1_000_000L;
+        Task task = new Task(object, function, parameters, intervalNanos, System.nanoTime() + intervalNanos);
+        synchronized (timers) {
+            timers.put(id, task);
+        }
 
         VsmxArray result = new VsmxArray(interpreter, 1);
         result.setPropertyValue(0, new VsmxNumber(interpreter, id));
@@ -71,9 +123,8 @@ public class Timer extends BaseNativeObject {
 
     public void clearInterval(VsmxBaseObject object, VsmxBaseObject id) {
         int idValue = id.getPropertyValue(0).getIntValue();
-        Thread thread = timers.remove(idValue);
-        if (thread != null) {
-            thread.interrupt();
+        synchronized (timers) {
+            timers.remove(idValue);
         }
     }
 }