com.google.appengine.tools.cloudstorage.RetryHelper.java Source code

Introduction

Here is the source code for com.google.appengine.tools.cloudstorage.RetryHelper.java

Source

/*
 * Copyright 2012 Google Inc. All Rights Reserved.
 *
 * Licensed 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.google.appengine.tools.cloudstorage;

import static java.util.concurrent.TimeUnit.MILLISECONDS;

import com.google.apphosting.api.ApiProxy.ApiProxyException;
import com.google.common.base.Stopwatch;

import java.io.FileNotFoundException;
import java.io.IOException;
import java.net.MalformedURLException;
import java.nio.channels.ClosedByInterruptException;
import java.util.logging.Logger;

/**
 * Utility class for retrying operations. For more details about the parameters, see
 * {@link RetryParams}
 *
 * If the request is never successful, a {@link RetriesExhaustedException} will be thrown.
 *
 * @author ohler@google.com (Christian Ohler)
 *
 * @param <V> return value of the closure that is being run with retries
 */
public class RetryHelper<V> {

    private static final Logger log = Logger.getLogger(RetryHelper.class.getName());

    private static String messageChain(Throwable t) {
        StringBuilder resultMessage = new StringBuilder("" + t);
        t = t.getCause();
        while (t != null) {
            resultMessage.append("\n -- caused by: " + t);
            t = t.getCause();
        }
        return "" + resultMessage;
    }

    /** Body to be run and retried if it doesn't succeed. */
    interface Body<V> {
        V run() throws IOException;
    }

    static class RetryInteruptedException extends RuntimeException {
        private static final long serialVersionUID = 1L;

        RetryInteruptedException() {
        }
    }

    private final Stopwatch stopwatch;
    private int attemptsSoFar = 0;
    private final Body<V> body;
    private final RetryParams retryParams;

    private RetryHelper(Body<V> body, RetryParams parms) {
        this(body, parms, new Stopwatch());
    }

    private RetryHelper(Body<V> body, RetryParams parms, Stopwatch stopwatch) {
        this.body = body;
        this.retryParams = parms;
        this.stopwatch = stopwatch;
    }

    @Override
    public String toString() {
        return getClass().getSimpleName() + "(" + stopwatch + ", " + attemptsSoFar + " attempts, " + body + ")";
    }

    private V doRetry() throws IOException {
        stopwatch.start();
        while (true) {
            attemptsSoFar++;
            Exception exception;
            try {
                V value = body.run();
                if (attemptsSoFar > 1) {
                    log.info(this + ": retry successful");
                }
                return value;
            } catch (IOException e) {
                if (e instanceof FileNotFoundException || e instanceof MalformedURLException
                        || e instanceof ClosedByInterruptException) {
                    throw e;
                }
                exception = e;
            } catch (ApiProxyException e) {
                exception = e;
            }
            long sleepDurationMillis = getSleepDuration(retryParams, attemptsSoFar);

            log.warning(this + ": Attempt " + attemptsSoFar + " failed, sleeping for " + sleepDurationMillis
                    + " ms: " + messageChain(exception));

            if (attemptsSoFar >= retryParams.getRetryMaxAttempts()
                    || (attemptsSoFar >= retryParams.getRetryMinAttempts()
                            && stopwatch.elapsed(MILLISECONDS) >= retryParams.getTotalRetryPeriodMillis())) {
                throw new RetriesExhaustedException(this + ": Too many failures, giving up", exception);
            }
            try {
                Thread.sleep(sleepDurationMillis);
            } catch (InterruptedException e2) {
                Thread.currentThread().interrupt();
                throw new RetryInteruptedException();
            }
        }
    }

    static long getSleepDuration(RetryParams retryParams, int attemptsSoFar) {
        return (long) ((Math.random() / 2.0 + .5) * (Math.min(retryParams.getMaxRetryDelayMillis(),
                Math.pow(retryParams.getRetryDelayBackoffFactor(), attemptsSoFar - 1)
                        * retryParams.getInitialRetryDelayMillis())));
    }

    public static <V> V runWithRetries(Body<V> body) throws IOException {
        return new RetryHelper<V>(body, RetryParams.getDefaultInstance()).doRetry();
    }

    public static <V> V runWithRetries(Body<V> body, RetryParams parms) throws IOException {
        return new RetryHelper<V>(body, parms).doRetry();
    }

    /**
     * For testing.
     */
    static <V> V runWithRetries(Body<V> body, RetryParams parms, Stopwatch stopwatch) throws IOException {
        return new RetryHelper<V>(body, parms, stopwatch).doRetry();
    }

}