Watcher: Mark watcher as started only after loading watches (#30403)

Starting watcher should wait for the watcher to be started before
marking the status as started, which is now done via a callback.

Also, reloading watcher could set the execution service to paused. This could
lead to watches not being executed, when run in tests. This fix does not
change the paused flag in the execution service, just clears out the
current queue and executions.

Closes #30381

x-pack/plugin/watcher/src/main/java/org/elasticsearch/xpack/watcher/WatcherLifeCycleService.java

@@ -110,8 +110,7 @@ public void clusterChanged(ClusterChangedEvent event) {
         // if this is not a data node, we need to start it ourselves possibly
         if (event.state().nodes().getLocalNode().isDataNode() == false &&
             isWatcherStoppedManually == false && this.state.get() == WatcherState.STOPPED) {
-            watcherService.start(event.state());
-            this.state.set(WatcherState.STARTED);
+            watcherService.start(event.state(), () -> this.state.set(WatcherState.STARTED));
             return;
         }
 
@@ -157,8 +156,8 @@ public void clusterChanged(ClusterChangedEvent event) {
                 if (state.get() == WatcherState.STARTED) {
                     watcherService.reload(event.state(), "new local watcher shard allocation ids");
                 } else if (state.get() == WatcherState.STOPPED) {
-                    watcherService.start(event.state());
-                    this.state.set(WatcherState.STARTED);
+                    this.state.set(WatcherState.STARTING);
+                    watcherService.start(event.state(), () -> this.state.set(WatcherState.STARTED));
                 }
             } else {
                 clearAllocationIds();

x-pack/plugin/watcher/src/main/java/org/elasticsearch/xpack/watcher/WatcherService.java

@@ -183,23 +183,40 @@ void reload(ClusterState state, String reason) {
         // by checking the cluster state version before and after loading the watches we can potentially just exit without applying the
         // changes
         processedClusterStateVersion.set(state.getVersion());
-        pauseExecution(reason);
         triggerService.pauseExecution();
+        int cancelledTaskCount = executionService.clearExecutionsAndQueue();
+        logger.info("reloading watcher, reason [{}], cancelled [{}] queued tasks", reason, cancelledTaskCount);
 
         executor.execute(wrapWatcherService(() -> reloadInner(state, reason, false),
             e -> logger.error("error reloading watcher", e)));
     }
 
-    public void start(ClusterState state) {
+    /**
+     * start the watcher service, load watches in the background
+     *
+     * @param state                     the current cluster state
+     * @param postWatchesLoadedCallback the callback to be triggered, when watches where loaded successfully
+     */
+    public void start(ClusterState state, Runnable postWatchesLoadedCallback) {
+        executionService.unPause();
         processedClusterStateVersion.set(state.getVersion());
-        executor.execute(wrapWatcherService(() -> reloadInner(state, "starting", true),
+        executor.execute(wrapWatcherService(() -> {
+                if (reloadInner(state, "starting", true)) {
+                    postWatchesLoadedCallback.run();
+                }
+            },
             e -> logger.error("error starting watcher", e)));
     }
 
     /**
-     * reload the watches and start scheduling them
+     * reload watches and start scheduling them
+     *
+     * @param state                 the current cluster state
+     * @param reason                the reason for reloading, will be logged
+     * @param loadTriggeredWatches  should triggered watches be loaded in this run, not needed for reloading, only for starting
+     * @return                      true if no other loading of a newer cluster state happened in parallel, false otherwise
      */
-    private synchronized void reloadInner(ClusterState state, String reason, boolean loadTriggeredWatches) {
+    private synchronized boolean reloadInner(ClusterState state, String reason, boolean loadTriggeredWatches) {
         // exit early if another thread has come in between
         if (processedClusterStateVersion.get() != state.getVersion()) {
             logger.debug("watch service has not been reloaded for state [{}], another reload for state [{}] in progress",
@@ -221,9 +238,11 @@ private synchronized void reloadInner(ClusterState state, String reason, boolean
                 executionService.executeTriggeredWatches(triggeredWatches);
             }
             logger.debug("watch service has been reloaded, reason [{}]", reason);
+            return true;
         } else {
             logger.debug("watch service has not been reloaded for state [{}], another reload for state [{}] in progress",
                 state.getVersion(), processedClusterStateVersion.get());
+            return false;
         }
     }
 

x-pack/plugin/watcher/src/main/java/org/elasticsearch/xpack/watcher/execution/ExecutionService.java

@@ -121,11 +121,25 @@ public void unPause() {
     }
 
     /**
-     * Pause the execution of the watcher executor
+     * Pause the execution of the watcher executor, and empty the state.
+     * Pausing means, that no new watch executions will be done unless this pausing is explicitely unset.
+     * This is important when watcher is stopped, so that scheduled watches do not accidentally get executed.
+     * This should not be used when we need to reload watcher based on some cluster state changes, then just calling
+     * {@link #clearExecutionsAndQueue()} is the way to go
+     *
      * @return the number of tasks that have been removed
      */
     public int pause() {
         paused.set(true);
+        return clearExecutionsAndQueue();
+    }
+
+    /**
+     * Empty the currently queued tasks and wait for current executions to finish.
+     *
+     * @return the number of tasks that have been removed
+     */
+    public int clearExecutionsAndQueue() {
         int cancelledTaskCount = executor.queue().drainTo(new ArrayList<>());
         this.clearExecutions();
         return cancelledTaskCount;

x-pack/plugin/watcher/src/test/java/org/elasticsearch/xpack/watcher/WatcherLifeCycleServiceTests.java

@@ -180,7 +180,7 @@ public void testManualStartStop() {
         reset(watcherService);
         when(watcherService.validate(clusterState)).thenReturn(true);
         lifeCycleService.clusterChanged(new ClusterChangedEvent("any", clusterState, stoppedClusterState));
-        verify(watcherService, times(1)).start(eq(clusterState));
+        verify(watcherService, times(1)).start(eq(clusterState), anyObject());
 
         // no change, keep going
         reset(watcherService);
@@ -423,7 +423,7 @@ public void testWatcherServiceDoesNotStartIfIndexTemplatesAreMissing() throws Ex
         when(watcherService.validate(eq(state))).thenReturn(true);
 
         lifeCycleService.clusterChanged(new ClusterChangedEvent("any", state, state));
-        verify(watcherService, times(0)).start(any(ClusterState.class));
+        verify(watcherService, times(0)).start(any(ClusterState.class), anyObject());
     }
 
     public void testWatcherStopsWhenMasterNodeIsMissing() {

x-pack/plugin/watcher/src/test/java/org/elasticsearch/xpack/watcher/WatcherServiceTests.java

@@ -68,6 +68,7 @@
 import static org.mockito.Matchers.any;
 import static org.mockito.Matchers.eq;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
@@ -199,7 +200,7 @@ void stopExecutor() {
         when(client.clearScroll(any(ClearScrollRequest.class))).thenReturn(clearScrollFuture);
         clearScrollFuture.onResponse(new ClearScrollResponse(true, 1));
 
-        service.start(clusterState);
+        service.start(clusterState, () -> {});
 
         ArgumentCaptor<List> captor = ArgumentCaptor.forClass(List.class);
         verify(triggerService).start(captor.capture());
@@ -238,6 +239,27 @@ void stopExecutor() {
         verify(triggerEngine).pauseExecution();
     }
 
+    // if we have to reload the watcher service, the execution service should not be paused, as this might
+    // result in missing executions
+    public void testReloadingWatcherDoesNotPauseExecutionService() {
+        ExecutionService executionService = mock(ExecutionService.class);
+        TriggerService triggerService = mock(TriggerService.class);
+        WatcherService service = new WatcherService(Settings.EMPTY, triggerService, mock(TriggeredWatchStore.class),
+            executionService, mock(WatchParser.class), mock(Client.class), executorService) {
+            @Override
+            void stopExecutor() {
+            }
+        };
+
+        ClusterState.Builder csBuilder = new ClusterState.Builder(new ClusterName("_name"));
+        csBuilder.metaData(MetaData.builder());
+
+        service.reload(csBuilder.build(), "whatever");
+        verify(executionService).clearExecutionsAndQueue();
+        verify(executionService, never()).pause();
+        verify(triggerService).pauseExecution();
+    }
+
     private static DiscoveryNode newNode() {
         return new DiscoveryNode("node", ESTestCase.buildNewFakeTransportAddress(), Collections.emptyMap(),
                 new HashSet<>(asList(DiscoveryNode.Role.values())), Version.CURRENT);

x-pack/plugin/watcher/src/test/java/org/elasticsearch/xpack/watcher/test/integration/ExecutionVarsIntegrationTests.java

@@ -23,6 +23,7 @@
 import java.util.Map;
 import java.util.function.Function;
 
+import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertHitCount;
 import static org.elasticsearch.xpack.watcher.actions.ActionBuilders.loggingAction;
 import static org.elasticsearch.xpack.watcher.client.WatchSourceBuilders.watchBuilder;
 import static org.elasticsearch.xpack.watcher.input.InputBuilders.simpleInput;
@@ -36,6 +37,8 @@
 
 public class ExecutionVarsIntegrationTests extends AbstractWatcherIntegrationTestCase {
 
+    private String watchId = randomAlphaOfLength(20);
+
     @Override
     protected List<Class<? extends Plugin>> pluginTypes() {
         List<Class<? extends Plugin>> types = super.pluginTypes();
@@ -107,7 +110,7 @@ protected Map<String, Function<Map<String, Object>, Object>> pluginScripts() {
     public void testVars() throws Exception {
         WatcherClient watcherClient = watcherClient();
 
-        PutWatchResponse putWatchResponse = watcherClient.preparePutWatch("_id").setSource(watchBuilder()
+        PutWatchResponse putWatchResponse = watcherClient.preparePutWatch(watchId).setSource(watchBuilder()
                 .trigger(schedule(cron("0/1 * * * * ?")))
                 .input(simpleInput("value", 5))
                 .condition(new ScriptCondition(
@@ -126,7 +129,7 @@ public void testVars() throws Exception {
 
         assertThat(putWatchResponse.isCreated(), is(true));
 
-        timeWarp().trigger("_id");
+        timeWarp().trigger(watchId);
 
         flush();
         refresh();
@@ -135,11 +138,11 @@ public void testVars() throws Exception {
             // defaults to match all;
         });
 
-        assertThat(searchResponse.getHits().getTotalHits(), is(1L));
+        assertHitCount(searchResponse, 1L);
 
         Map<String, Object> source = searchResponse.getHits().getAt(0).getSourceAsMap();
 
-        assertValue(source, "watch_id", is("_id"));
+        assertValue(source, "watch_id", is(watchId));
         assertValue(source, "state", is("executed"));
 
         // we don't store the computed vars in history
@@ -171,7 +174,7 @@ public void testVars() throws Exception {
     public void testVarsManual() throws Exception {
         WatcherClient watcherClient = watcherClient();
 
-        PutWatchResponse putWatchResponse = watcherClient.preparePutWatch("_id").setSource(watchBuilder()
+        PutWatchResponse putWatchResponse = watcherClient.preparePutWatch(watchId).setSource(watchBuilder()
                 .trigger(schedule(cron("0/1 * * * * ? 2020")))
                 .input(simpleInput("value", 5))
                 .condition(new ScriptCondition(
@@ -193,13 +196,13 @@ public void testVarsManual() throws Exception {
         boolean debug = randomBoolean();
 
         ExecuteWatchResponse executeWatchResponse = watcherClient
-                .prepareExecuteWatch("_id")
+                .prepareExecuteWatch(watchId)
                 .setDebug(debug)
                 .get();
         assertThat(executeWatchResponse.getRecordId(), notNullValue());
         XContentSource source = executeWatchResponse.getRecordSource();
 
-        assertValue(source, "watch_id", is("_id"));
+        assertValue(source, "watch_id", is(watchId));
         assertValue(source, "state", is("executed"));
 
         if (debug) {