You are viewing a plain text version of this content. The canonical link for it is here.
Posted to commits@helix.apache.org by xy...@apache.org on 2023/05/20 01:44:18 UTC
[helix] branch metaclient updated: Add leader election API and dummy class (#2488)
This is an automated email from the ASF dual-hosted git repository.
xyuanlu pushed a commit to branch metaclient
in repository https://gitbox.apache.org/repos/asf/helix.git
The following commit(s) were added to refs/heads/metaclient by this push:
new 2d3800a7a Add leader election API and dummy class (#2488)
2d3800a7a is described below
commit 2d3800a7a1f2637328c5aa0a5617a68c330e45f1
Author: xyuanlu <xy...@gmail.com>
AuthorDate: Fri May 19 18:44:12 2023 -0700
Add leader election API and dummy class (#2488)
---
.../leaderelection/LeaderElectionClient.java | 180 +++++++++++++++++++++
.../LeaderElectionListenerInterface.java | 32 ++++
.../recipes/leaderelection/LeaderInfo.java | 45 ++++++
3 files changed, 257 insertions(+)
diff --git a/meta-client/src/main/java/org/apache/helix/metaclient/recipes/leaderelection/LeaderElectionClient.java b/meta-client/src/main/java/org/apache/helix/metaclient/recipes/leaderelection/LeaderElectionClient.java
new file mode 100644
index 000000000..4f609153b
--- /dev/null
+++ b/meta-client/src/main/java/org/apache/helix/metaclient/recipes/leaderelection/LeaderElectionClient.java
@@ -0,0 +1,180 @@
+package org.apache.helix.metaclient.recipes.leaderelection;
+
+/*
+ * 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.List;
+
+import org.apache.helix.metaclient.api.MetaClientInterface;
+import org.apache.helix.metaclient.factories.MetaClientConfig;
+
+
+/**
+ * LeaderElectionClient does distributed leader election using CRUD and change notification APIs
+ * provided by underlying metadata client. Leader election config can provide many
+ * configs like base path for all participating nodes, sync/async mode, TTL etc.
+ *
+ * Participants join a leader election group by calling the following API.
+ * The Leader Election client maintains and elect an active leader from participant pool.
+ * All participants wanted to be elected as leader joins a pool.
+ * LeaderElection client maintains an active leader, by monitoring liveness of current leader and
+ * re-elect if needed and user no need to call elect or re-elect explicitly.
+ * This LeaderElection client will notify registered listeners for any leadership change.
+ *
+ * One client is created per each participant(host). One participant can join multiple leader
+ * election groups using the same client.
+ * When the client is used by a leader election service, one client is created for each participant.
+ *
+ */
+public class LeaderElectionClient {
+
+ /**
+ * Construct a LeaderElectionClient using a user passed in leaderElectionConfig. It creates a MetaClient
+ * instance underneath.
+ * When MetaClient is auto closed be cause of being disconnected and auto retry connection timed out, A new
+ * MetaClient instance will be created and keeps retry connection.
+ *
+ * @param metaClientConfig The config used to create an metaclient.
+ */
+ public LeaderElectionClient(MetaClientConfig metaClientConfig, String participant) {
+
+ }
+
+ /**
+ * Construct a LeaderElectionClient using a user passed in MetaClient object
+ * When MetaClient is auto closed be cause of being disconnected and auto retry connection timed out, user
+ * will need to create a new MetaClient and a new LeaderElectionClient instance.
+ *
+ * @param metaClient metaClient object to be used.
+ */
+ public LeaderElectionClient(MetaClientInterface metaClient, String participant) {
+
+ }
+
+ /**
+ * Returns true if current participant is the current leadership.
+ */
+ public boolean isLeader(String leaderPath) {
+ return false;
+ }
+
+ /**
+ * Participants join a leader election group by calling the following API.
+ * The Leader Election client maintains and elect an active leader from the participant pool.
+ *
+ * @param leaderPath The path for leader election.
+ * @return boolean indicating if the operation is succeeded.
+ */
+ public boolean joinLeaderElectionParticipantPool(String leaderPath) {
+ return false;
+ }
+
+ /**
+ * Participants join a leader election group by calling the following API.
+ * The Leader Election client maintains and elect an active leader from the participant pool.
+ *
+ * @param leaderPath The path for leader election.
+ * @param userInfo Any additional information to associate with this participant.
+ * @return boolean indicating if the operation is succeeded.
+ */
+ public boolean joinLeaderElectionParticipantPool(String leaderPath, Object userInfo) {
+ return false;
+ }
+
+ /**
+ * Any participant may exit the exitLeaderElectionParticipantPool by calling the API.
+ * If the participant is not the current leader, it leaves the pool and won't participant future
+ * leader election process.
+ * If the participant is the current leader, it leaves the pool and a new leader will be elected
+ * if there are other participants in the pool.
+ * Throws exception if the participant is not in the pool.
+ *
+ * @param leaderPath The path for leader election.
+ * @return boolean indicating if the operation is succeeded.
+ *
+ * @throws RuntimeException If the participant did not join participant pool via this client. // TODO: define exp type
+ */
+ public boolean exitLeaderElectionParticipantPool(String leaderPath) {
+ return false;
+ }
+
+ /**
+ * Releases leadership for participant.
+ *
+ * @param leaderPath The path for leader election.
+ *
+ * @throws RuntimeException if the leadership is not owned by this participant, or if the
+ * participant did not join participant pool via this client. // TODO: define exp type
+ */
+ public void relinquishLeader(String leaderPath) {
+ }
+
+ /**
+ * Get current leader.
+ *
+ * @param leaderPath The path for leader election.
+ * @return Returns the current leader. Return null if no Leader at a given point.
+ * @throws RuntimeException when leader path does not exist. // TODO: define exp type
+ */
+ public String getLeader(String leaderPath) {
+ return null;
+ }
+
+ /**
+ * Return a list of hosts in participant pool
+ *
+ * @param leaderPath The path for leader election.
+ * @return a list of participant(s) that tried to elect themselves as leader. The current leader
+ * is not included in the list.
+ * Return an empty list if
+ * 1. There is a leader for this path but there is no other participants
+ * 2. There is no leader for this path at the time of query
+ * @throws RuntimeException when leader path does not exist. // TODO: define exp type
+ */
+ public List<String> getParticipants(String leaderPath) {
+ return null;
+ }
+
+ /**
+ * APIs to register/unregister listener to leader path. All the participants can listen to any
+ * leaderPath, Including leader going down or a new leader comes up.
+ * Whenever current leader for that leaderPath goes down (considering it's ephemeral entity which
+ * get's auto-deleted after TTL or session timeout) or a new leader comes up, it notifies all
+ * participants who have been listening on entryChange event.
+ *
+ * An listener will still be installed if the path does not exists yet.
+ *
+ * @param leaderPath The path for leader election that listener is interested for change.
+ * @param listener An implementation of LeaderElectionListenerInterface
+ * @return an boolean value indicating if registration is success.
+ */
+ public boolean subscribeLeadershipChanges(String leaderPath,
+ LeaderElectionListenerInterface listener) {
+ return false;
+ }
+
+ /**
+ * @param leaderPath The path for leader election that listener is no longer interested for change.
+ * @param listener An implementation of LeaderElectionListenerInterface
+ */
+ public void unsubscribeLeadershipChanges(String leaderPath,
+ LeaderElectionListenerInterface listener) {
+ }
+}
+
diff --git a/meta-client/src/main/java/org/apache/helix/metaclient/recipes/leaderelection/LeaderElectionListenerInterface.java b/meta-client/src/main/java/org/apache/helix/metaclient/recipes/leaderelection/LeaderElectionListenerInterface.java
new file mode 100644
index 000000000..0436e1eb0
--- /dev/null
+++ b/meta-client/src/main/java/org/apache/helix/metaclient/recipes/leaderelection/LeaderElectionListenerInterface.java
@@ -0,0 +1,32 @@
+package org.apache.helix.metaclient.recipes.leaderelection;
+
+/*
+ * 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.
+ */
+
+/**
+ * It provides APIs for listener listening on events like a new leader is created or current
+ * leader node is deleted.
+ */
+public interface LeaderElectionListenerInterface {
+ // When new leader is elected:
+ // noLeader (null) -> has leader (new leader name)
+ // When existing leader not leader anymore:
+ // has Leader (prevleader name) -> no leader (null)
+ public void onLeadershipChange(String leaderPath, String prevLeader, String curLeader);
+}
\ No newline at end of file
diff --git a/meta-client/src/main/java/org/apache/helix/metaclient/recipes/leaderelection/LeaderInfo.java b/meta-client/src/main/java/org/apache/helix/metaclient/recipes/leaderelection/LeaderInfo.java
new file mode 100644
index 000000000..9e817c1c9
--- /dev/null
+++ b/meta-client/src/main/java/org/apache/helix/metaclient/recipes/leaderelection/LeaderInfo.java
@@ -0,0 +1,45 @@
+package org.apache.helix.metaclient.recipes.leaderelection;
+
+/*
+ * 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 org.apache.helix.metaclient.datamodel.DataRecord;
+
+
+/**
+ * This is the data represent leader election info of a leader election path.
+ */
+public class LeaderInfo {
+
+ private String _leaderElectionGroupName;
+ private final DataRecord _record;
+
+
+ public LeaderInfo( String leaderElectionGroupName) {
+ _leaderElectionGroupName = leaderElectionGroupName;
+ _record = new DataRecord(_leaderElectionGroupName);
+ }
+
+ public enum LeaderAttribute {
+ LEADER_NAME,
+ PARTICIPANTS
+ }
+
+
+}