org.zkybase.kite.guard.ConcurrencyThrottleTemplate.java Source code

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Here is the source code for org.zkybase.kite.guard.ConcurrencyThrottleTemplate.java

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/*
 * 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.guard;

import java.util.concurrent.Semaphore;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.jmx.export.annotation.ManagedAttribute;
import org.springframework.jmx.export.annotation.ManagedResource;
import org.zkybase.kite.AbstractGuard;
import org.zkybase.kite.GuardCallback;
import org.zkybase.kite.exception.ConcurrencyLimitExceededException;

/**
 * <p>
 * Guard that fails with an exception when a concurrency threshold is exceeded.
 * </p>
 * <p>
 * Implementation is based on a counting semaphore.
 * </p>
 * <p>
 * We expose this guard as a JMX MBean so it can be queried and manipulated in management contexts.
 * </p>
 * 
 * @author Willie Wheeler (willie.wheeler@gmail.com)
 * @since 1.0
 */
@ManagedResource
public class ConcurrencyThrottleTemplate extends AbstractGuard {
    private static Logger log = LoggerFactory.getLogger(ConcurrencyThrottleTemplate.class);

    private final int limit;
    private final Semaphore semaphore;

    /**
     * Creates a concurrency throttle with the given limit. The throttle rejects requests in excess of the limit.
     * 
     * @param limit concurrency limit
     * @throws IllegalArgumentException if limit &lt; 1
     */
    public ConcurrencyThrottleTemplate(int limit) {
        if (limit < 1) {
            throw new IllegalArgumentException("limit must be >= 1");
        }
        this.limit = limit;
        this.semaphore = new Semaphore(limit, true);
    }

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

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