Prevent multiple submissions in SimpleMetrics

Author: NonSwag

core/src/main/java/org/faststats/SimpleMetrics.java

@@ -30,6 +30,11 @@ protected void startSubmitting(int initialDelay, int period, TimeUnit unit) {
             return;
         }
 
+        if (isSubmitting()) {
+            debug("Metrics already submitting, not starting again");
+            return;
+        }
+
         this.executor = Executors.newSingleThreadScheduledExecutor(runnable -> {
             var thread = new Thread(runnable, "metrics-submitter");
             thread.setDaemon(true);
@@ -40,6 +45,10 @@ protected void startSubmitting(int initialDelay, int period, TimeUnit unit) {
         executor.scheduleAtFixedRate(this::submitData, initialDelay, period, unit);
     }
 
+    protected boolean isSubmitting() {
+        return executor != null && !executor.isShutdown();
+    }
+
     @Override
     public void addChart(Chart<?> chart) {
         charts.add(chart);