/*
* 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.addthis.basis.net;
import javax.naming.ServiceUnavailableException;
import java.io.IOException;
import com.addthis.basis.net.http.HttpResponse;
import com.addthis.basis.util.AdjustableSemaphore;
import org.apache.http.client.methods.HttpRequestBase;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* This class is a wrapper class for HttpUtil that gates the execute method with an adjustable semaphore.
* When limit is reached, any attempts to send request result in <link>ServiceUnavailableException</link> being thrown.
*/
public class ConstrainedHttpClient {
private static final Logger logger = LoggerFactory.getLogger(ConstrainedHttpClient.class);
protected AdjustableSemaphore semaphore;
public ConstrainedHttpClient(int maxConcurrentRequests) {
semaphore = new AdjustableSemaphore(maxConcurrentRequests);
}
/**
* Executes the http method specified while protecting the http client with a semaphore. If the maximum number
* of outstanding requests has been reached it will throw a ServiceUnavailableException. The other exceptions are
* thrown by the standard http client executeMethod.
*
* @return
* @throws ServiceUnavailableException If the limit of concurrent connections has been reached.
* @throws IOException If an I/O (transport) error occurs. Some transport exceptions cannot be recovered from.
*/
public HttpResponse execute(HttpRequestBase request, int timeoutms) throws ServiceUnavailableException, IOException {
if (semaphore.tryAcquire()) {
try {
logger.trace("Semaphore was acquired. Remaining: {} ", semaphore.availablePermits());
return HttpUtil.execute(request, timeoutms);
} finally {
semaphore.release();
}
} else {
throw new ServiceUnavailableException("Reached limit of " + getCurrentRequests() + " concurrent requests");
}
}
/**
* @return Returns the number of outstanding requests that have not returned yet from http client.
*/
public int getCurrentRequests() {
return semaphore.maxPermits() - semaphore.availablePermits();
}
/**
* Resets the maximum allowed concurrent requests
*
* @param maxConcurrentRequests - the new maximum
*/
public void setMaxConcurrentRequests(int maxConcurrentRequests) {
semaphore.setMaxPermits(maxConcurrentRequests);
}
}