| /** |
| * 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.tools.util; |
| |
| import org.apache.commons.logging.Log; |
| import org.apache.commons.logging.LogFactory; |
| import org.apache.hadoop.io.retry.RetryPolicy; |
| import org.apache.hadoop.io.retry.RetryPolicy.RetryAction; |
| import org.apache.hadoop.io.retry.RetryPolicies; |
| import org.apache.hadoop.util.ThreadUtil; |
| |
| import java.io.IOException; |
| import java.util.concurrent.TimeUnit; |
| |
| /** |
| * This class represents commands that be retried on failure, in a configurable |
| * manner. |
| */ |
| public abstract class RetriableCommand { |
| |
| private static Log LOG = LogFactory.getLog(RetriableCommand.class); |
| |
| private static final long DELAY_MILLISECONDS = 500; |
| private static final int MAX_RETRIES = 3; |
| |
| private RetryPolicy retryPolicy = RetryPolicies. |
| exponentialBackoffRetry(MAX_RETRIES, DELAY_MILLISECONDS, TimeUnit.MILLISECONDS); |
| protected String description; |
| |
| /** |
| * Constructor. |
| * @param description The human-readable description of the command. |
| */ |
| public RetriableCommand(String description) { |
| this.description = description; |
| } |
| |
| /** |
| * Constructor. |
| * @param description The human-readable description of the command. |
| * @param retryPolicy The RetryHandler to be used to compute retries. |
| */ |
| public RetriableCommand(String description, RetryPolicy retryPolicy) { |
| this(description); |
| setRetryPolicy(retryPolicy); |
| } |
| |
| /** |
| * Implement this interface-method define the command-logic that will be |
| * retried on failure (i.e. with Exception). |
| * @param arguments Argument-list to the command. |
| * @return Generic "Object". |
| * @throws Exception Throws Exception on complete failure. |
| */ |
| protected abstract Object doExecute(Object... arguments) throws Exception; |
| |
| /** |
| * The execute() method invokes doExecute() until either: |
| * 1. doExecute() succeeds, or |
| * 2. the command may no longer be retried (e.g. runs out of retry-attempts). |
| * @param arguments The list of arguments for the command. |
| * @return Generic "Object" from doExecute(), on success. |
| * @throws IOException, IOException, on complete failure. |
| */ |
| public Object execute(Object... arguments) throws Exception { |
| Exception latestException; |
| int counter = 0; |
| while (true) { |
| try { |
| return doExecute(arguments); |
| } catch(Exception exception) { |
| LOG.error("Failure in Retriable command: " + description, exception); |
| latestException = exception; |
| } |
| counter++; |
| RetryAction action = retryPolicy.shouldRetry(latestException, counter, 0, true); |
| if (action.action == RetryPolicy.RetryAction.RetryDecision.RETRY) { |
| ThreadUtil.sleepAtLeastIgnoreInterrupts(action.delayMillis); |
| } else { |
| break; |
| } |
| } |
| |
| throw new IOException("Couldn't run retriable-command: " + description, |
| latestException); |
| } |
| |
| /** |
| * Fluent-interface to change the RetryHandler. |
| * @param retryHandler The new RetryHandler instance to be used. |
| * @return Self. |
| */ |
| public RetriableCommand setRetryPolicy(RetryPolicy retryHandler) { |
| this.retryPolicy = retryHandler; |
| return this; |
| } |
| } |