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This is a small extension to Google's Guava library to allow for the creation of configurable retrying strategies for an arbitrary function call, such as something that talks to a remote service with flaky uptime.

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/*
 * Copyright 2012-2013 Ray Holder
 *
 * 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.github.rholder.retry;

import com.google.common.base.Preconditions;
import com.google.common.util.concurrent.SimpleTimeLimiter;
import com.google.common.util.concurrent.TimeLimiter;

import javax.annotation.Nonnull;
import javax.annotation.concurrent.Immutable;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.TimeUnit;

/**
 * Factory class for instances of {@link AttemptTimeLimiter}
 * @author Jason Dunkelberger (dirkraft)
 */
public class AttemptTimeLimiters {

    private AttemptTimeLimiters(){
    }

    /**
     * @return an {@link AttemptTimeLimiter} impl which has no time limit
     */
    public static  AttemptTimeLimiter noTimeLimit() {
        return new NoAttemptTimeLimit();
    }

    /**
     * For control over thread management, it is preferable to offer an {@link ExecutorService} through the other
     * factory method, {@link #fixedTimeLimit(long, TimeUnit, ExecutorService)}. See the note on
     * {@link SimpleTimeLimiter#SimpleTimeLimiter(ExecutorService)}, which this AttemptTimeLimiter uses.
     * @param duration that an attempt may persist before being circumvented
     * @param timeUnit of the 'duration' arg
     * @return an {@link AttemptTimeLimiter} with a fixed time limit for each attempt
     */
    public static  AttemptTimeLimiter fixedTimeLimit(long duration, @Nonnull TimeUnit timeUnit) {
        Preconditions.checkNotNull(timeUnit);
        return new FixedAttemptTimeLimit(duration, timeUnit);
    }

    /**
     * @param duration that an attempt may persist before being circumvented
     * @param timeUnit of the 'duration' arg
     * @param executorService used to enforce time limit
     * @return an {@link AttemptTimeLimiter} with a fixed time limit for each attempt
     */
    public static  AttemptTimeLimiter fixedTimeLimit(long duration, @Nonnull TimeUnit timeUnit, @Nonnull ExecutorService executorService) {
        Preconditions.checkNotNull(timeUnit);
        return new FixedAttemptTimeLimit(duration, timeUnit, executorService);
    }

    @Immutable
    private static final class NoAttemptTimeLimit implements AttemptTimeLimiter {
        @Override
        public V call(Callable callable) throws Exception {
            return callable.call();
        }
    }

    @Immutable
    private static final class FixedAttemptTimeLimit implements AttemptTimeLimiter {

        private final TimeLimiter timeLimiter;
        private final long duration;
        private final TimeUnit timeUnit;

        public FixedAttemptTimeLimit(long duration, @Nonnull TimeUnit timeUnit) {
            this(new SimpleTimeLimiter(), duration, timeUnit);
        }

        public FixedAttemptTimeLimit(long duration, @Nonnull TimeUnit timeUnit, @Nonnull ExecutorService executorService) {
            this(new SimpleTimeLimiter(executorService), duration, timeUnit);
        }

        private FixedAttemptTimeLimit(@Nonnull TimeLimiter timeLimiter, long duration, @Nonnull TimeUnit timeUnit) {
            Preconditions.checkNotNull(timeLimiter);
            Preconditions.checkNotNull(timeUnit);
            this.timeLimiter = timeLimiter;
            this.duration = duration;
            this.timeUnit = timeUnit;
        }

        @Override
        public V call(Callable callable) throws Exception {
            return timeLimiter.callWithTimeout(callable, duration, timeUnit, true);
        }
    }
}