Cancel auto-reload runnable at configuration shutdown

Avoid having multiple auto-reload runnable when
the configuration is shut down and restarted.
The situation happens quite often when the configuration
is reloaded and generates unnecessary extra concurrency
on the configuration objects other than increasingly consuming
additional tasks.

Bug: Issue 11187
Change-Id: Ic03ce3fceb0df746d20437ae7cf4d2a8f4822d02

src/main/java/com/googlesource/gerrit/plugins/replication/AutoReloadConfigDecorator.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/AutoReloadConfigDecorator.java b/src/main/java/com/googlesource/gerrit/plugins/replication/AutoReloadConfigDecorator.java
index a09b0c9..6b42464 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/AutoReloadConfigDecorator.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/AutoReloadConfigDecorator.java
@@ -29,6 +29,7 @@
 import java.util.List;
 import java.util.Optional;
 import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.ScheduledFuture;
 import java.util.concurrent.TimeUnit;
 import org.eclipse.jgit.errors.ConfigInvalidException;
 import org.eclipse.jgit.transport.URIish;
@@ -50,6 +51,7 @@
   // ReplicationConfig
   private final Provider<ReplicationQueue> replicationQueue;
   private final ScheduledExecutorService autoReloadExecutor;
+  private ScheduledFuture<?> autoReloadRunnable;
 
   @Inject
   public AutoReloadConfigDecorator(
@@ -144,13 +146,18 @@
 
   @Override
   public synchronized int shutdown() {
+    if (autoReloadRunnable != null) {
+      autoReloadRunnable.cancel(false);
+      autoReloadRunnable = null;
+    }
     return currentConfig.shutdown();
   }
 
   @Override
   public synchronized void startup(WorkQueue workQueue) {
     currentConfig.startup(workQueue);
-    autoReloadExecutor.scheduleAtFixedRate(
-        this::reloadIfNeeded, RELOAD_DELAY, RELOAD_INTERVAL, TimeUnit.SECONDS);
+    autoReloadRunnable =
+        autoReloadExecutor.scheduleAtFixedRate(
+            this::reloadIfNeeded, RELOAD_DELAY, RELOAD_INTERVAL, TimeUnit.SECONDS);
   }
 }