WorkQueue: Add a convenience method for scheduling a periodic background job

This saves some common boilerplate code.

Change-Id: I475bc2d31c32c2138f690ef455d0734e1fcfa074
Signed-off-by: Edwin Kempin <ekempin@google.com>

java/com/google/gerrit/server/account/AccountDeactivator.java

@@ -26,8 +26,6 @@ import com.google.gerrit.server.query.account.InternalAccountQuery;
 import com.google.inject.Inject;
 import com.google.inject.Provider;
 import java.util.Optional;
-import java.util.concurrent.Future;
-import java.util.concurrent.TimeUnit;
 import org.eclipse.jgit.lib.Config;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -63,15 +61,7 @@ public class AccountDeactivator implements Runnable {
       if (!supportAutomaticAccountActivityUpdate) {
         return;
       }
-      schedule.ifPresent(
-          s -> {
-            @SuppressWarnings("unused")
-            Future<?> possiblyIgnoredError =
-                queue
-                    .getDefaultQueue()
-                    .scheduleAtFixedRate(
-                        deactivator, s.initialDelay(), s.interval(), TimeUnit.MILLISECONDS);
-          });
+      schedule.ifPresent(s -> queue.scheduleAtFixedRate(deactivator, s));
     }
 
     @Override

java/com/google/gerrit/server/change/ChangeCleanupRunner.java

@@ -25,8 +25,6 @@ import com.google.gerrit.server.util.ManualRequestContext;
 import com.google.gerrit.server.util.OneOffRequestContext;
 import com.google.gwtorm.server.OrmException;
 import com.google.inject.Inject;
-import java.util.concurrent.Future;
-import java.util.concurrent.TimeUnit;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -55,16 +53,7 @@ public class ChangeCleanupRunner implements Runnable {
 
     @Override
     public void start() {
-      cfg.getSchedule()
-          .ifPresent(
-              s -> {
-                @SuppressWarnings("unused")
-                Future<?> possiblyIgnoredError =
-                    queue
-                        .getDefaultQueue()
-                        .scheduleAtFixedRate(
-                            runner, s.initialDelay(), s.interval(), TimeUnit.MILLISECONDS);
-              });
+      cfg.getSchedule().ifPresent(s -> queue.scheduleAtFixedRate(runner, s));
     }
 
     @Override

java/com/google/gerrit/server/git/GarbageCollectionRunner.java

@@ -19,8 +19,6 @@ import com.google.gerrit.extensions.events.LifecycleListener;
 import com.google.gerrit.server.config.GcConfig;
 import com.google.gerrit.server.project.ProjectCache;
 import com.google.inject.Inject;
-import java.util.concurrent.Future;
-import java.util.concurrent.TimeUnit;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -42,17 +40,7 @@ public class GarbageCollectionRunner implements Runnable {
 
     @Override
     public void start() {
-      gcConfig
-          .getSchedule()
-          .ifPresent(
-              s -> {
-                @SuppressWarnings("unused")
-                Future<?> possiblyIgnoredError =
-                    queue
-                        .getDefaultQueue()
-                        .scheduleAtFixedRate(
-                            gcRunner, s.initialDelay(), s.interval(), TimeUnit.MILLISECONDS);
-              });
+      gcConfig.getSchedule().ifPresent(s -> queue.scheduleAtFixedRate(gcRunner, s));
     }
 
     @Override

java/com/google/gerrit/server/git/WorkQueue.java

@@ -18,6 +18,7 @@ import com.google.gerrit.extensions.events.LifecycleListener;
 import com.google.gerrit.lifecycle.LifecycleModule;
 import com.google.gerrit.reviewdb.client.Project;
 import com.google.gerrit.server.config.GerritServerConfig;
+import com.google.gerrit.server.config.ScheduleConfig.Schedule;
 import com.google.gerrit.server.util.IdGenerator;
 import com.google.inject.Inject;
 import com.google.inject.Singleton;
@@ -130,6 +131,15 @@ public class WorkQueue {
     return executor;
   }
 
+  /** Executes a periodic command at a fixed schedule on the default queue. */
+  public void scheduleAtFixedRate(Runnable command, Schedule schedule) {
+    @SuppressWarnings("unused")
+    Future<?> possiblyIgnoredError =
+        getDefaultQueue()
+            .scheduleAtFixedRate(
+                command, schedule.initialDelay(), schedule.interval(), TimeUnit.MILLISECONDS);
+  }
+
   /** Get all of the tasks currently scheduled in any work queue. */
   public List<Task<?>> getTasks() {
     final List<Task<?>> r = new ArrayList<>();

java/com/google/gerrit/server/group/PeriodicGroupIndexer.java

@@ -32,7 +32,6 @@ import com.google.gerrit.server.group.db.GroupNameNotes;
 import com.google.gerrit.server.index.group.GroupIndexer;
 import com.google.inject.Inject;
 import com.google.inject.Provider;
-import java.util.concurrent.Future;
 import java.util.concurrent.TimeUnit;
 import org.eclipse.jgit.lib.Config;
 import org.eclipse.jgit.lib.Repository;
@@ -98,12 +97,7 @@ public class PeriodicGroupIndexer implements Runnable {
               .setSubsection("scheduledIndexer")
               .buildSchedule()
               .orElseGet(() -> Schedule.createOrFail(TimeUnit.MINUTES.toMillis(5), "00:00"));
-      @SuppressWarnings("unused")
-      Future<?> possiblyIgnoredError =
-          queue
-              .getDefaultQueue()
-              .scheduleAtFixedRate(
-                  runner, schedule.initialDelay(), schedule.interval(), TimeUnit.MILLISECONDS);
+      queue.scheduleAtFixedRate(runner, schedule);
     }
 
     @Override