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Posted to commits@helix.apache.org by jx...@apache.org on 2022/03/24 16:51:15 UTC
[helix] 01/02: Add event handler and event listener interface (#1976)
This is an automated email from the ASF dual-hosted git repository.
jxue pushed a commit to branch helix-vm-freeze
in repository https://gitbox.apache.org/repos/asf/helix.git
commit 3f4c7bde519dd8da493bf42dea9fb7aecfaf72d2
Author: Molly Gao <31...@users.noreply.github.com>
AuthorDate: Thu Mar 10 14:05:33 2022 -0800
Add event handler and event listener interface (#1976)
This commit creates a skeleton for event handling framework and adds the following classes:
CloudEventListener interface
CloudEventHandler class
CloudEventHandlerFactory class
---
.../helix/cloud/event/CloudEventHandler.java | 97 ++++++++++++++++++++++
.../cloud/event/CloudEventHandlerFactory.java | 45 ++++++++++
.../helix/cloud/event/CloudEventListener.java | 48 +++++++++++
3 files changed, 190 insertions(+)
diff --git a/helix-core/src/main/java/org/apache/helix/cloud/event/CloudEventHandler.java b/helix-core/src/main/java/org/apache/helix/cloud/event/CloudEventHandler.java
new file mode 100644
index 0000000..295194b
--- /dev/null
+++ b/helix-core/src/main/java/org/apache/helix/cloud/event/CloudEventHandler.java
@@ -0,0 +1,97 @@
+package org.apache.helix.cloud.event;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Optional;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * This class implements a wrapper around multiple {@link CloudEventListener}, and arrange them by
+ * 1. PreEventHandlerCallback -> only one allowed
+ * 2. Unordered CloudEventListener list -> multiple allowed
+ * 3. PostEventHandlerCallback -> only one allowed
+ * to enable an easy management of event listeners and callbacks.
+ */
+public class CloudEventHandler {
+ private static final Logger LOG = LoggerFactory.getLogger(CloudEventHandler.class.getName());
+ private List<CloudEventListener> _unorderedEventListenerList = new ArrayList<>();
+ private Optional<CloudEventListener> _preEventHandlerCallback;
+ private Optional<CloudEventListener> _postEventHandlerCallback;
+
+ /**
+ * Register an event listener to the event handler.
+ * If no listener type is specified, register as an unordered listener.
+ * @param listener
+ */
+ public void registerCloudEventListener(CloudEventListener listener) {
+ if (listener != null) {
+ switch (listener.getListenerType()) {
+ case PRE_EVENT_HANDLER:
+ _preEventHandlerCallback = Optional.of(listener);
+ break;
+ case POST_EVENT_HANDLER:
+ _postEventHandlerCallback = Optional.of(listener);
+ break;
+ case UNORDERED:
+ default:
+ _unorderedEventListenerList.add(listener);
+ break;
+ }
+ }
+ }
+
+ /**
+ * Unregister an event listener to the event handler.
+ * @param listener
+ */
+ public void unregisterCloudEventListener(CloudEventListener listener) {
+ _unorderedEventListenerList.remove(listener);
+ }
+
+ /**
+ * Trigger the callback / listeners in order of
+ * 1. PreEventHandlerCallback
+ * 2. Unordered CloudEventListener list
+ * 3. PostEventHandlerCallback
+ * @param eventInfo the object contains any information about the incoming event
+ */
+ public void onPause(Object eventInfo) {
+ _preEventHandlerCallback.ifPresent(callback -> callback.onPause(eventInfo));
+ _unorderedEventListenerList.parallelStream().forEach(listener -> listener.onPause(eventInfo));
+ _postEventHandlerCallback.ifPresent(callback -> callback.onPause(eventInfo));
+ }
+
+ /**
+ * Trigger the callback / listeners in order of
+ * 1. PreEventHandlerCallback
+ * 2. Unordered CloudEventListener list
+ * 3. PostEventHandlerCallback
+ * @param eventInfo the object contains any information about the incoming event
+ */
+ public void onResume(Object eventInfo) {
+ _preEventHandlerCallback.ifPresent(callback -> callback.onResume(eventInfo));
+ _unorderedEventListenerList.parallelStream().forEach(listener -> listener.onResume(eventInfo));
+ _postEventHandlerCallback.ifPresent(callback -> callback.onResume(eventInfo));
+ }
+}
diff --git a/helix-core/src/main/java/org/apache/helix/cloud/event/CloudEventHandlerFactory.java b/helix-core/src/main/java/org/apache/helix/cloud/event/CloudEventHandlerFactory.java
new file mode 100644
index 0000000..1b1a53c
--- /dev/null
+++ b/helix-core/src/main/java/org/apache/helix/cloud/event/CloudEventHandlerFactory.java
@@ -0,0 +1,45 @@
+package org.apache.helix.cloud.event;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+/**
+ * This class is the factory for singleton class {@link CloudEventHandler}
+ */
+public class CloudEventHandlerFactory {
+ private static CloudEventHandler INSTANCE = null;
+
+ private CloudEventHandlerFactory() {
+ }
+
+ /**
+ * Get a CloudEventHandler instance
+ * @return
+ */
+ public static CloudEventHandler getInstance() {
+ if (INSTANCE == null) {
+ synchronized (CloudEventHandlerFactory.class) {
+ if (INSTANCE == null) {
+ INSTANCE = new CloudEventHandler();
+ }
+ }
+ }
+ return INSTANCE;
+ }
+}
diff --git a/helix-core/src/main/java/org/apache/helix/cloud/event/CloudEventListener.java b/helix-core/src/main/java/org/apache/helix/cloud/event/CloudEventListener.java
new file mode 100644
index 0000000..b4adcc3
--- /dev/null
+++ b/helix-core/src/main/java/org/apache/helix/cloud/event/CloudEventListener.java
@@ -0,0 +1,48 @@
+package org.apache.helix.cloud.event;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+/**
+ * This class is a basic unit for callbacks to handle events.
+ * The listeners can be registered to {@link CloudEventHandler}.
+ */
+public interface CloudEventListener {
+ enum ListenerType {
+ PRE_EVENT_HANDLER, UNORDERED, POST_EVENT_HANDLER
+ }
+
+ /**
+ * Callback for when a pause event is incoming
+ * @param eventInfo the info of the incoming event
+ */
+ void onPause(Object eventInfo);
+
+ /**
+ * Callback for when a pause event finishes
+ * @param eventInfo the info of the incoming event
+ */
+ void onResume(Object eventInfo);
+
+ /**
+ * Get the listener type of a listener
+ * @return the type of the listener
+ */
+ ListenerType getListenerType();
+}