org.apache.hadoop.io.retry.FailoverProxyProvider Maven / Gradle / Ivy
/*
* 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.
*/
package org.apache.hadoop.io.retry;
import java.io.Closeable;
import org.apache.hadoop.classification.InterfaceStability;
/**
* An implementer of this interface is capable of providing proxy objects for
* use in IPC communication, and potentially modifying these objects or creating
* entirely new ones in the event of certain types of failures. The
* determination of whether or not to fail over is handled by
* {@link RetryPolicy}.
*/
@InterfaceStability.Evolving
public interface FailoverProxyProvider extends Closeable {
static class ProxyInfo {
public T proxy;
/*
* The information (e.g., the IP address) of the current proxy object. It
* provides information for debugging purposes.
*/
public String proxyInfo;
public ProxyInfo(T proxy, String proxyInfo) {
this.proxy = proxy;
this.proxyInfo = proxyInfo;
}
private String proxyName() {
return proxy != null ? proxy.getClass().getSimpleName() : "UnknownProxy";
}
public String getString(String methodName) {
return proxyName() + "." + methodName + " over " + proxyInfo;
}
@Override
public String toString() {
return proxyName() + " over " + proxyInfo;
}
}
/**
* Get the proxy object which should be used until the next failover event
* occurs.
*
* @return the proxy object to invoke methods upon
*/
public ProxyInfo getProxy();
/**
* Called whenever the associated {@link RetryPolicy} determines that an error
* warrants failing over.
*
* @param currentProxy
* the proxy object which was being used before this failover event
*/
public void performFailover(T currentProxy);
/**
* Return a reference to the interface this provider's proxy objects actually
* implement. If any of the methods on this interface are annotated as being
* {@link Idempotent} or {@link AtMostOnce}, then this fact will be passed to
* the {@link RetryPolicy#shouldRetry(Exception, int, int, boolean)} method on
* error, for use in determining whether or not failover should be attempted.
*
* @return the interface implemented by the proxy objects returned by
* {@link FailoverProxyProvider#getProxy()}
*/
public Class getInterface();
}