com.datastax.oss.driver.api.core.metadata.NodeStateListener Maven / Gradle / Ivy
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* Licensed to the Apache Software Foundation (ASF) under one
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* 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.
*/
package com.datastax.oss.driver.api.core.metadata;
import com.datastax.oss.driver.api.core.loadbalancing.NodeDistance;
import com.datastax.oss.driver.api.core.session.Session;
import com.datastax.oss.driver.api.core.session.SessionBuilder;
import edu.umd.cs.findbugs.annotations.NonNull;
/**
* A listener that gets notified when nodes states change.
*
* Implementations of this interface can be registered either via the configuration (see {@code
* reference.conf} in the manual or core driver JAR), or programmatically via {@link
* SessionBuilder#addNodeStateListener(NodeStateListener)}.
*
*
Note that the methods defined by this interface will be executed by internal driver threads,
* and are therefore expected to have short execution times. If you need to perform long
* computations or blocking calls in response to schema change events, it is strongly recommended to
* schedule them asynchronously on a separate thread provided by your application code.
*
*
If you implement this interface but don't need to implement all the methods, extend {@link
* NodeStateListenerBase}.
*
*
If your implementation of this interface requires access to a fully-initialized session,
* consider wrapping it in a {@link SafeInitNodeStateListener}.
*/
public interface NodeStateListener extends AutoCloseable {
/**
* Invoked when a node is first added to the cluster.
*
*
The node is not up yet at this point. {@link #onUp(Node)} will be notified later if the
* driver successfully connects to the node (provided that a session is opened and the node is not
* {@link NodeDistance#IGNORED ignored}), or receives a topology event for it.
*
*
This method is not invoked for the contact points provided at initialization. It is
* however for new nodes discovered during the full node list refresh after the first connection.
*/
void onAdd(@NonNull Node node);
/** Invoked when a node's state switches to {@link NodeState#UP}. */
void onUp(@NonNull Node node);
/**
* Invoked when a node's state switches to {@link NodeState#DOWN} or {@link
* NodeState#FORCED_DOWN}.
*/
void onDown(@NonNull Node node);
/**
* Invoked when a node leaves the cluster.
*
*
This can be triggered by a topology event, or during a full node list refresh if the node is
* absent from the new list.
*/
void onRemove(@NonNull Node node);
/**
* Invoked when the session is ready to process user requests.
*
*
This corresponds to the moment when {@link SessionBuilder#build()} returns, or the future
* returned by {@link SessionBuilder#buildAsync()} completes. If the session initialization fails,
* this method will not get called.
*
*
Listener methods are invoked from different threads; if you store the session in a field,
* make it at least volatile to guarantee proper publication.
*
*
Note that this method will not be the first one invoked on the listener; the driver emits
* node events before that, during the initialization of the session:
*
*
* - First the driver shuffles the contact points, and tries each one sequentially. For any
* contact point that can't be reached, {@link #onDown(Node)} is invoked; for the one that
* eventually succeeds, {@link #onUp(Node)} is invoked and that node becomes the control
* node (if none succeeds, the session initialization fails and the process stops here).
*
- The control node's {@code system.peers} table is inspected to discover the remaining
* nodes in the cluster. For any node that wasn't already a contact point, {@link
* #onAdd(Node)} is invoked; for any contact point that doesn't have a corresponding entry
* in the table, {@link #onRemove(Node)} is invoked;
*
- The load balancing policy computes the nodes' {@linkplain NodeDistance distances}, and,
* for each LOCAL or REMOTE node, the driver creates a connection pool. If at least one
* pooled connection can be established, {@link #onUp(Node)} is invoked; otherwise, {@link
* #onDown(Node)} is invoked (no additional event is emitted for the control node, it is
* considered up since we already have a connection to it).
*
- Once all the pools are created, the session is fully initialized and this method is
* invoked.
*
*
* If you're not interested in those init events, or want to delay them until after the session is
* ready, take a look at {@link SafeInitNodeStateListener}.
*
* This method's default implementation is empty.
*/
default void onSessionReady(@NonNull Session session) {}
}