org.zkybase.kite.throttle.ThrottleTemplate.java Source code

Introduction

Here is the source code for org.zkybase.kite.throttle.ThrottleTemplate.java

Source

/*
 * Copyright (c) 2010 the original author or authors.
 *
 * 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.zkybase.kite.throttle;

import java.util.concurrent.Semaphore;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.BeanNameAware;
import org.springframework.jmx.export.annotation.ManagedAttribute;
import org.springframework.jmx.export.annotation.ManagedResource;

/**
 * <p>
 * Template component that fails with an exception when a concurrency threshold
 * is exceeded.
 * </p>
 * <p>
 * Implementation is based on a counting semaphore.
 * </p>
 * 
 * @author Willie Wheeler
 * @since 1.0
 */
@ManagedResource
public class ThrottleTemplate implements BeanNameAware {
    private static Logger log = LoggerFactory.getLogger(ThrottleTemplate.class);

    private String beanName;
    private final int limit;
    private final Semaphore semaphore;

    /**
     * @param limit
     * @throws IllegalArgumentException if limit &lt; 1
     */
    public ThrottleTemplate(int limit) {
        if (limit < 1) {
            throw new IllegalArgumentException("limit must be >= 1");
        }
        this.limit = limit;
        this.semaphore = new Semaphore(limit, true);
    }

    @ManagedAttribute(description = "Throttle name")
    public String getBeanName() {
        return beanName;
    }

    public void setBeanName(String beanName) {
        this.beanName = beanName;
    }

    @ManagedAttribute(description = "Concurrency limit, after which requests are rejected")
    public int getLimit() {
        return limit;
    }

    public <T> T execute(ThrottleCallback<T> action) throws Exception {
        log.debug("Entered concurrency throttle");
        try {
            if (semaphore.tryAcquire()) {
                try {
                    return action.doInThrottle();
                } finally {
                    semaphore.release();
                }
            } else {
                log.warn("Request rejected: concurrency limit {} exceeded", limit);
                throw new ConcurrencyLimitExceededException(limit);
            }
        } finally {
            log.debug("Exiting concurrency throttle");
        }
    }
}