//
// ========================================================================
// Copyright (c) 1995-2017 Mort Bay Consulting Pty. Ltd.
// ------------------------------------------------------------------------
// All rights reserved. This program and the accompanying materials
// are made available under the terms of the Eclipse Public License v1.0
// and Apache License v2.0 which accompanies this distribution.
//
// The Eclipse Public License is available at
// http://www.eclipse.org/legal/epl-v10.html
//
// The Apache License v2.0 is available at
// http://www.opensource.org/licenses/apache2.0.php
//
// You may elect to redistribute this code under either of these licenses.
// ========================================================================
//
package org.eclipse.jetty.servlets;
import java.io.IOException;
import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;
import javax.servlet.AsyncContext;
import javax.servlet.AsyncEvent;
import javax.servlet.AsyncListener;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import org.eclipse.jetty.server.handler.ContextHandler;
import org.eclipse.jetty.util.annotation.ManagedAttribute;
import org.eclipse.jetty.util.annotation.ManagedObject;
import org.eclipse.jetty.util.log.Log;
import org.eclipse.jetty.util.log.Logger;
/**
* Quality of Service Filter.
* <p>
* This filter limits the number of active requests to the number set by the "maxRequests" init parameter (default 10).
* If more requests are received, they are suspended and placed on priority queues. Priorities are determined by
* the {@link #getPriority(ServletRequest)} method and are a value between 0 and the value given by the "maxPriority"
* init parameter (default 10), with higher values having higher priority.
* <p>
* This filter is ideal to prevent wasting threads waiting for slow/limited
* resources such as a JDBC connection pool. It avoids the situation where all of a
* containers thread pool may be consumed blocking on such a slow resource.
* By limiting the number of active threads, a smaller thread pool may be used as
* the threads are not wasted waiting. Thus more memory may be available for use by
* the active threads.
* <p>
* Furthermore, this filter uses a priority when resuming waiting requests. So that if
* a container is under load, and there are many requests waiting for resources,
* the {@link #getPriority(ServletRequest)} method is used, so that more important
* requests are serviced first. For example, this filter could be deployed with a
* maxRequest limit slightly smaller than the containers thread pool and a high priority
* allocated to admin users. Thus regardless of load, admin users would always be
* able to access the web application.
* <p>
* The maxRequest limit is policed by a {@link Semaphore} and the filter will wait a short while attempting to acquire
* the semaphore. This wait is controlled by the "waitMs" init parameter and allows the expense of a suspend to be
* avoided if the semaphore is shortly available. If the semaphore cannot be obtained, the request will be suspended
* for the default suspend period of the container or the valued set as the "suspendMs" init parameter.
* <p>
* If the "managedAttr" init parameter is set to true, then this servlet is set as a {@link ServletContext} attribute with the
* filter name as the attribute name. This allows context external mechanism (eg JMX via {@link ContextHandler#MANAGED_ATTRIBUTES}) to
* manage the configuration of the filter.
*/
@ManagedObject("Quality of Service Filter")
public class QoSFilter implements Filter
{
private static final Logger LOG = Log.getLogger(QoSFilter.class);
static final int __DEFAULT_MAX_PRIORITY = 10;
static final int __DEFAULT_PASSES = 10;
static final int __DEFAULT_WAIT_MS = 50;
static final long __DEFAULT_TIMEOUT_MS = -1;
static final String MANAGED_ATTR_INIT_PARAM = "managedAttr";
static final String MAX_REQUESTS_INIT_PARAM = "maxRequests";
static final String MAX_PRIORITY_INIT_PARAM = "maxPriority";
static final String MAX_WAIT_INIT_PARAM = "waitMs";
static final String SUSPEND_INIT_PARAM = "suspendMs";
private final String _suspended = "QoSFilter@" + Integer.toHexString(hashCode()) + ".SUSPENDED";
private final String _resumed = "QoSFilter@" + Integer.toHexString(hashCode()) + ".RESUMED";
private long _waitMs;
private long _suspendMs;
private int _maxRequests;
private Semaphore _passes;
private Queue<AsyncContext>[] _queues;
private AsyncListener[] _listeners;
public void init(FilterConfig filterConfig)
{
int max_priority = __DEFAULT_MAX_PRIORITY;
if (filterConfig.getInitParameter(MAX_PRIORITY_INIT_PARAM) != null)
max_priority = Integer.parseInt(filterConfig.getInitParameter(MAX_PRIORITY_INIT_PARAM));
_queues = new Queue[max_priority + 1];
_listeners = new AsyncListener[_queues.length];
for (int p = 0; p < _queues.length; ++p)
{
_queues[p] = new ConcurrentLinkedQueue<>();
_listeners[p] = new QoSAsyncListener(p);
}
int maxRequests = __DEFAULT_PASSES;
if (filterConfig.getInitParameter(MAX_REQUESTS_INIT_PARAM) != null)
maxRequests = Integer.parseInt(filterConfig.getInitParameter(MAX_REQUESTS_INIT_PARAM));
_passes = new Semaphore(maxRequests, true);
_maxRequests = maxRequests;
long wait = __DEFAULT_WAIT_MS;
if (filterConfig.getInitParameter(MAX_WAIT_INIT_PARAM) != null)
wait = Integer.parseInt(filterConfig.getInitParameter(MAX_WAIT_INIT_PARAM));
_waitMs = wait;
long suspend = __DEFAULT_TIMEOUT_MS;
if (filterConfig.getInitParameter(SUSPEND_INIT_PARAM) != null)
suspend = Integer.parseInt(filterConfig.getInitParameter(SUSPEND_INIT_PARAM));
_suspendMs = suspend;
ServletContext context = filterConfig.getServletContext();
if (context != null && Boolean.parseBoolean(filterConfig.getInitParameter(MANAGED_ATTR_INIT_PARAM)))
context.setAttribute(filterConfig.getFilterName(), this);
}
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException
{
boolean accepted = false;
try
{
Boolean suspended = (Boolean)request.getAttribute(_suspended);
if (suspended == null)
{
accepted = _passes.tryAcquire(getWaitMs(), TimeUnit.MILLISECONDS);
if (accepted)
{
request.setAttribute(_suspended, Boolean.FALSE);
if (LOG.isDebugEnabled())
LOG.debug("Accepted {}", request);
}
else
{
request.setAttribute(_suspended, Boolean.TRUE);
int priority = getPriority(request);
AsyncContext asyncContext = request.startAsync();
long suspendMs = getSuspendMs();
if (suspendMs > 0)
asyncContext.setTimeout(suspendMs);
asyncContext.addListener(_listeners[priority]);
_queues[priority].add(asyncContext);
if (LOG.isDebugEnabled())
LOG.debug("Suspended {}", request);
return;
}
}
else
{
if (suspended)
{
request.setAttribute(_suspended, Boolean.FALSE);
Boolean resumed = (Boolean)request.getAttribute(_resumed);
if (resumed == Boolean.TRUE)
{
_passes.acquire();
accepted = true;
if (LOG.isDebugEnabled())
LOG.debug("Resumed {}", request);
}
else
{
// Timeout! try 1 more time.
accepted = _passes.tryAcquire(getWaitMs(), TimeUnit.MILLISECONDS);
if (LOG.isDebugEnabled())
LOG.debug("Timeout {}", request);
}
}
else
{
// Pass through resume of previously accepted request.
_passes.acquire();
accepted = true;
if (LOG.isDebugEnabled())
LOG.debug("Passthrough {}", request);
}
}
if (accepted)
{
chain.doFilter(request, response);
}
else
{
if (LOG.isDebugEnabled())
LOG.debug("Rejected {}", request);
((HttpServletResponse)response).sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE);
}
}
catch (InterruptedException e)
{
((HttpServletResponse)response).sendError(HttpServletResponse.SC_SERVICE_UNAVAILABLE);
}
finally
{
if (accepted)
{
for (int p = _queues.length - 1; p >= 0; --p)
{
AsyncContext asyncContext = _queues[p].poll();
if (asyncContext != null)
{
ServletRequest candidate = asyncContext.getRequest();
Boolean suspended = (Boolean)candidate.getAttribute(_suspended);
if (suspended == Boolean.TRUE)
{
candidate.setAttribute(_resumed, Boolean.TRUE);
asyncContext.dispatch();
break;
}
}
}
_passes.release();
}
}
}
/**
* Computes the request priority.
* <p>
* The default implementation assigns the following priorities:
* <ul>
* <li> 2 - for an authenticated request
* <li> 1 - for a request with valid / non new session
* <li> 0 - for all other requests.
* </ul>
* This method may be overridden to provide application specific priorities.
*
* @param request the incoming request
* @return the computed request priority
*/
protected int getPriority(ServletRequest request)
{
HttpServletRequest baseRequest = (HttpServletRequest)request;
if (baseRequest.getUserPrincipal() != null)
{
return 2;
}
else
{
HttpSession session = baseRequest.getSession(false);
if (session != null && !session.isNew())
return 1;
else
return 0;
}
}
public void destroy()
{
}
/**
* Get the (short) amount of time (in milliseconds) that the filter would wait
* for the semaphore to become available before suspending a request.
*
* @return wait time (in milliseconds)
*/
@ManagedAttribute("(short) amount of time filter will wait before suspending request (in ms)")
public long getWaitMs()
{
return _waitMs;
}
/**
* Set the (short) amount of time (in milliseconds) that the filter would wait
* for the semaphore to become available before suspending a request.
*
* @param value wait time (in milliseconds)
*/
public void setWaitMs(long value)
{
_waitMs = value;
}
/**
* Get the amount of time (in milliseconds) that the filter would suspend
* a request for while waiting for the semaphore to become available.
*
* @return suspend time (in milliseconds)
*/
@ManagedAttribute("amount of time filter will suspend a request for while waiting for the semaphore to become available (in ms)")
public long getSuspendMs()
{
return _suspendMs;
}
/**
* Set the amount of time (in milliseconds) that the filter would suspend
* a request for while waiting for the semaphore to become available.
*
* @param value suspend time (in milliseconds)
*/
public void setSuspendMs(long value)
{
_suspendMs = value;
}
/**
* Get the maximum number of requests allowed to be processed
* at the same time.
*
* @return maximum number of requests
*/
@ManagedAttribute("maximum number of requests to allow processing of at the same time")
public int getMaxRequests()
{
return _maxRequests;
}
/**
* Set the maximum number of requests allowed to be processed
* at the same time.
*
* @param value the number of requests
*/
public void setMaxRequests(int value)
{
_passes = new Semaphore((value - getMaxRequests() + _passes.availablePermits()), true);
_maxRequests = value;
}
private class QoSAsyncListener implements AsyncListener
{
private final int priority;
public QoSAsyncListener(int priority)
{
this.priority = priority;
}
@Override
public void onStartAsync(AsyncEvent event) throws IOException
{
}
@Override
public void onComplete(AsyncEvent event) throws IOException
{
}
@Override
public void onTimeout(AsyncEvent event) throws IOException
{
// Remove before it's redispatched, so it won't be
// redispatched again at the end of the filtering.
AsyncContext asyncContext = event.getAsyncContext();
_queues[priority].remove(asyncContext);
asyncContext.dispatch();
}
@Override
public void onError(AsyncEvent event) throws IOException
{
}
}
}