utils/misc/src/main/java/org/onlab/util/RetryingFunction.java

/*
 * Copyright 2015 Open Networking Laboratory
 *
 * 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 org.onlab.util;

import java.util.function.Function;

import com.google.common.base.Throwables;

import static org.onlab.util.SonarSuppressionConstants.SONAR_CATCH_THROWABLE;

/**
 * Function that retries execution on failure.
 *
 * @param <U> input type
 * @param <V> output type
 */
public class RetryingFunction<U, V> implements Function<U, V> {

    private final Function<U, V> baseFunction;
    private final Class<? extends Throwable> exceptionClass;
    private final int maxRetries;
    private final int maxDelayBetweenRetries;

    public RetryingFunction(Function<U, V> baseFunction,
            Class<? extends Throwable> exceptionClass,
            int maxRetries,
            int maxDelayBetweenRetries) {
        this.baseFunction = baseFunction;
        this.exceptionClass = exceptionClass;
        this.maxRetries = maxRetries;
        this.maxDelayBetweenRetries = maxDelayBetweenRetries;
    }

    @SuppressWarnings(SONAR_CATCH_THROWABLE)
    // Yes we really do want to catch Throwable
    @Override
    public V apply(U input) {
        int retryAttempts = 0;
        while (true) {
            try {
                return baseFunction.apply(input);
            } catch (Throwable t) {
                if (!exceptionClass.isAssignableFrom(t.getClass()) || retryAttempts == maxRetries) {
                    Throwables.propagate(t);
                }
                Tools.randomDelay(maxDelayBetweenRetries);
                retryAttempts++;
            }
        }
    }
}