fix the module shutdown order, fixes #533

core/kamon-core/src/main/scala/kamon/module/ModuleRegistry.scala

@@ -24,8 +24,8 @@ import java.util.concurrent.atomic.AtomicReference
 import com.typesafe.config.Config
 import kamon.module.Module.Registration
 import kamon.status.Status
-import kamon.metric.MetricRegistry
-import kamon.trace.Tracer
+import kamon.metric.{MetricRegistry, PeriodSnapshot}
+import kamon.trace.{Span, Tracer}
 import kamon.util.Clock
 import org.slf4j.LoggerFactory
 
@@ -128,8 +128,7 @@ class ModuleRegistry(configuration: Configuration, clock: Clock, metricRegistry:
     */
   def stopModules(): Future[Unit] = synchronized {
     implicit val cleanupExecutor = ExecutionContext.Implicits.global
-    scheduleMetricsTicker(once = true)
-    scheduleSpansTicker(once = true)
+    stopReporterTickers()
 
     var stoppedSignals: List[Future[Unit]] = Nil
     _registeredModules.dropWhile {
@@ -151,7 +150,7 @@ class ModuleRegistry(configuration: Configuration, clock: Clock, metricRegistry:
     * all available metric reporting modules. If a ticker was already scheduled then that scheduled job will be
     * cancelled and scheduled again.
     */
-  private def scheduleMetricsTicker(once: Boolean = false): Unit = {
+  private def scheduleMetricsTicker(): Unit = {
     val currentMetricsTicker = _metricsTickerSchedule.get()
     if(currentMetricsTicker != null)
       currentMetricsTicker.cancel(false)
@@ -171,24 +170,14 @@ class ModuleRegistry(configuration: Configuration, clock: Clock, metricRegistry:
           val currentInstant = Instant.now(clock)
           val periodSnapshot = metricRegistry.snapshot(resetState = true)
 
-          metricReporterModules().foreach { entry =>
-            Future {
-              try entry.module.reportPeriodSnapshot(periodSnapshot) catch { case error: Throwable =>
-                _logger.error(s"Reporter [${entry.name}] failed to process a metrics tick.", error)
-              }
-            }(entry.executionContext)
-          }
-
+          metricReporterModules().foreach(entry => scheduleMetricsTick(entry, periodSnapshot))
           lastInstant = currentInstant
         } catch {
           case NonFatal(t) => _logger.error("Failed to run a metrics tick", t)
         }
       }
 
-      if(once)
-        _metricsTickerExecutor.schedule(ticker, 0L, TimeUnit.MILLISECONDS)
-      else
-        _metricsTickerExecutor.scheduleAtFixedRate(ticker, initialDelay, interval, TimeUnit.MILLISECONDS)
+      _metricsTickerExecutor.scheduleAtFixedRate(ticker, initialDelay, interval, TimeUnit.MILLISECONDS)
     }
   }
 
@@ -197,7 +186,7 @@ class ModuleRegistry(configuration: Configuration, clock: Clock, metricRegistry:
     * all available span reporting modules. If a ticker was already scheduled then that scheduled job will be
     * cancelled and scheduled again.
     */
-  private def scheduleSpansTicker(once: Boolean = false): Unit = {
+  private def scheduleSpansTicker(): Unit = {
     val currentSpansTicker = _spansTickerSchedule.get()
     if(currentSpansTicker != null)
       currentSpansTicker.cancel(false)
@@ -208,27 +197,43 @@ class ModuleRegistry(configuration: Configuration, clock: Clock, metricRegistry:
       val ticker = new Runnable {
         override def run(): Unit = try {
           val spanBatch = tracer.spans()
-
-          spanReporterModules().foreach { entry =>
-            Future {
-              try entry.module.reportSpans(spanBatch) catch { case error: Throwable =>
-                _logger.error(s"Reporter [${entry.name}] failed to process a spans tick.", error)
-              }
-            }(entry.executionContext)
-          }
+          spanReporterModules().foreach(entry => scheduleSpansBatch(entry, spanBatch))
 
         } catch {
           case NonFatal(t) => _logger.error("Failed to run a spans tick", t)
         }
       }
 
-      if(once)
-        _spansTickerExecutor.schedule(ticker, 0L, TimeUnit.MILLISECONDS)
-      else
-        _spansTickerExecutor.scheduleAtFixedRate(ticker, interval, interval, TimeUnit.MILLISECONDS)
+      _spansTickerExecutor.scheduleAtFixedRate(ticker, interval, interval, TimeUnit.MILLISECONDS)
     }
   }
 
+  private def scheduleMetricsTick(entry: Entry[MetricReporter], periodSnapshot: PeriodSnapshot): Unit = {
+    Future {
+      try entry.module.reportPeriodSnapshot(periodSnapshot) catch { case error: Throwable =>
+        _logger.error(s"Reporter [${entry.name}] failed to process a metrics tick.", error)
+      }
+    }(entry.executionContext)
+  }
+
+  private def scheduleSpansBatch(entry: Entry[SpanReporter], spanBatch: Seq[Span.Finished]): Unit = {
+    Future {
+      try entry.module.reportSpans(spanBatch) catch { case error: Throwable =>
+        _logger.error(s"Reporter [${entry.name}] failed to process a spans tick.", error)
+      }
+    }(entry.executionContext)
+  }
+
+  private def stopReporterTickers(): Unit = {
+    val currentMetricsTicker = _metricsTickerSchedule.get()
+    if(currentMetricsTicker != null)
+      currentMetricsTicker.cancel(false)
+
+    val currentSpansTicker = _spansTickerSchedule.get()
+    if(currentSpansTicker != null)
+      currentSpansTicker.cancel(false)
+  }
+
   private def metricReporterModules(): Iterable[Entry[MetricReporter]] = synchronized {
     _metricReporterModules.values
   }
@@ -368,10 +373,14 @@ class ModuleRegistry(configuration: Configuration, clock: Clock, metricRegistry:
 
     // Remove the module from all registries
     _registeredModules = _registeredModules - entry.name
-    if(entry.module.isInstanceOf[MetricReporter])
+    if(entry.module.isInstanceOf[MetricReporter]) {
       _metricReporterModules = _metricReporterModules - entry.name
-    if(entry.module.isInstanceOf[SpanReporter])
+      scheduleMetricsTick(entry.asInstanceOf[Entry[MetricReporter]], metricRegistry.snapshot(resetState = false))
+    }
+    if(entry.module.isInstanceOf[SpanReporter]) {
       _spanReporterModules = _spanReporterModules - entry.name
+      scheduleSpansBatch(entry.asInstanceOf[Entry[SpanReporter]], tracer.spans())
+    }
 
 
     // Schedule a call to stop on the module