org.cloudifysource.esc.driver.provisioning.RequestRateLimiter.java Source code

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Here is the source code for org.cloudifysource.esc.driver.provisioning.RequestRateLimiter.java

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/*******************************************************************************
 * Copyright (c) 2013 GigaSpaces Technologies Ltd. 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 org.cloudifysource.esc.driver.provisioning;

import java.util.concurrent.TimeUnit;
import java.util.logging.Logger;

import com.google.common.util.concurrent.RateLimiter;

/**
 * This rate limiter is designed to allow a specific number of request attempts in a defined period of time.
 * in-case the request limit exceeds, block method will block the current thread until the cool-down 
 * period has ended. The implementation uses the {@link com.google.common.util.concurrent.RateLimiter}
 * to determine the actual cool-down period of the throttling according to the time frame specified.
 * 
 * 
 * @author adaml
 * @since 2.7.0
 *
 */
public class RequestRateLimiter {

    private final int numRequests;
    private final RateLimiter throttler;
    private final Logger logger = Logger.getLogger(RequestRateLimiter.class.getName());

    private int requestCounter;

    /**
     * 
     * @param numRequests - the number of allowed requests in the given time frame.
     * @param timeFrame - the timeframe limit for number of requests
     * @param unit - time unit.
     */
    public RequestRateLimiter(final int numRequests, final long timeFrame, final TimeUnit unit) {
        this.numRequests = numRequests;
        this.throttler = RateLimiter.create(1.0 / unit.toSeconds(timeFrame));
    }

    /**
     * initializes the request rate limiter upon first block request in rotation. 
     */
    private void init() {
        boolean acquired = this.throttler.tryAcquire();
        if (acquired) {
            this.throttler.acquire();
        }
    }

    /**
     * 
     * @return true if blocking was preformed.
     */
    public boolean block() {
        incrementRetryCounter();
        if (isInitRequired()) {
            init();
        }
        if (isThrottlingRequired()) {
            logger.fine("Request limit has been reached. Rate limit is being enforced.");
            throttler.acquire();
            logger.fine("Rate limit enforcement has ended.");
            return true;
        }
        return false;
    }

    // is this the first block attempt in the rotation?
    private boolean isInitRequired() {
        if ((this.requestCounter % this.getNumRequests()) == 1) {
            return true;
        }
        return false;
    }

    /**
     * 
     * @return true if blocking is required.
     */
    public boolean tryBlock() {
        return isThrottlingRequired();
    }

    private boolean isThrottlingRequired() {
        if ((this.requestCounter % this.getNumRequests()) == 0) {
            return true;
        }
        return false;
    }

    private synchronized void incrementRetryCounter() {
        this.requestCounter = this.requestCounter + 1;
    }

    /**
     * Returns the defined duration for consequtive requests.
     * 
     * @return the defined duration for consequtive requests.
     */
    public long getDuration() {
        return (long) (1.0 / this.throttler.getRate());
    }

    public int getNumRequests() {
        return numRequests;
    }

    /**
     * returns the remaining retries until block.
     * 
     * @return 
     *       remaining retries until block.
     */
    public int getRemainingRetries() {
        return numRequests - (this.requestCounter % numRequests);
    }
}