[SDCISA-15833, swisspost#170] Fully prevent 'onDone()' from being cal…

…led too often.

src/main/java/org/swisspush/redisques/scheduling/PeriodicSkipScheduler.java

@@ -1,6 +1,7 @@
 package org.swisspush.redisques.scheduling;
 
 import io.vertx.core.Handler;
+import io.vertx.core.Promise;
 import io.vertx.core.Vertx;
 import org.slf4j.Logger;
 
@@ -48,16 +49,15 @@ private void onTrigger(Timer timer) {
             return;
         }
         timer.begEpochMs = currentTimeMillis();
-        boolean oldValue = timer.isPending.getAndSet(true);
-        assert !oldValue : "Why is this already pending?";
         timer.task.accept(timer::onTaskDone_);
+        Promise<Void> p = Promise.promise();
+        var fut = p.future();
+        fut.onSuccess((Void v) -> timer.onTaskDone_());
+        fut.onFailure(ex -> log.error("This is expected to be UNREACHABLE", ex));
+        timer.task.accept(p::complete);
     }
 
     private void onTaskDone(Timer timer) {
-        boolean oldVal = timer.isPending.getAndSet(false);
-        if (!oldVal) {
-            throw new IllegalStateException("MUST NOT be called multiple times!");
-        }
         timer.endEpochMs = currentTimeMillis();
     }
 
@@ -71,7 +71,6 @@ public class Timer {
         private long id;
         // When the last run has begun and end.
         private long begEpochMs, endEpochMs;
-        private final AtomicBoolean isPending = new AtomicBoolean();
 
         private Timer(Consumer<Runnable> task) {
             this.task = task;