com.spotify.folsom.retry.RetryingClient.java Source code

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Here is the source code for com.spotify.folsom.retry.RetryingClient.java

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/*
 * Copyright (c) 2014-2015 Spotify AB
 *
 * 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.spotify.folsom.retry;

import com.google.common.util.concurrent.AsyncFunction;
import com.google.common.util.concurrent.Futures;
import com.google.common.util.concurrent.ListenableFuture;
import com.spotify.folsom.ConnectionChangeListener;
import com.spotify.folsom.MemcacheClosedException;
import com.spotify.folsom.RawMemcacheClient;
import com.spotify.folsom.client.Request;

/**
 * A simple wrapping client that retries once (but only for MemcacheClosedException's).
 * This helps avoid some transient problems when a node suddenly stops. It's mostly useful
 * in combination with a client that internally routes to multiple nodes such as
 * the Ketama client or RoundRobin client. It won't prevent all MemcacheClosedException's from
 * propagating, it will just reduce the frequency in some cases.
 *
 * The retrying is intentionally strict about when to retry and how many times to retries in order
 * to minimize risk of causing more problems then it would solve.
 */
public class RetryingClient implements RawMemcacheClient {

    private final RawMemcacheClient delegate;

    public RetryingClient(final RawMemcacheClient delegate) {
        this.delegate = delegate;
    }

    @Override
    public <T> ListenableFuture<T> send(final Request<T> request) {
        final ListenableFuture<T> future = delegate.send(request);
        return Futures.catchingAsync(future, MemcacheClosedException.class,
                new AsyncFunction<MemcacheClosedException, T>() {
                    @Override
                    public ListenableFuture<T> apply(final MemcacheClosedException e) {
                        if (delegate.isConnected()) {
                            return delegate.send(request);
                        } else {
                            return Futures.immediateFailedFuture(e);
                        }
                    }
                });
    }

    @Override
    public void shutdown() {
        delegate.shutdown();
    }

    @Override
    public boolean isConnected() {
        return delegate.isConnected();
    }

    @Override
    public int numTotalConnections() {
        return delegate.numTotalConnections();
    }

    @Override
    public int numActiveConnections() {
        return delegate.numActiveConnections();
    }

    @Override
    public void registerForConnectionChanges(ConnectionChangeListener listener) {
        delegate.registerForConnectionChanges(listener);
    }

    @Override
    public void unregisterForConnectionChanges(ConnectionChangeListener listener) {
        delegate.unregisterForConnectionChanges(listener);
    }

    @Override
    public String toString() {
        return "Retrying(" + delegate + ")";
    }

}