org.eclipse.jetty.servlets
Class QoSFilter

java.lang.Object
  org.eclipse.jetty.servlets.QoSFilter

All Implemented Interfaces:

Filter

public class QoSFilter
extends Object
implements Filter

Quality of Service Filter. 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 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.

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.

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 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.

The maxRequest limit is policed by a 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.

If the "managedAttr" init parameter is set to true, then this servlet is set as a ServletContext attribute with the filter name as the attribute name. This allows context external mechanism (eg JMX via ContextHandler.MANAGED_ATTRIBUTES) to manage the configuration of the filter.

Field Summary

protected int	_maxRequests
protected long	_suspendMs
protected long	_waitMs

Constructor Summary

QoSFilter()

Method Summary

void	destroy()
void	doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
int	getMaxRequests() Get the maximum number of requests allowed to be processed at the same time.
protected int	getPriority(ServletRequest request) Get the request Priority.
long	getSuspendMs() Get the amount of time (in milliseconds) that the filter would suspend a request for while waiting for the semaphore to become available.
long	getWaitMs() Get the (short) amount of time (in milliseconds) that the filter would wait for the semaphore to become available before suspending a request.
void	init(FilterConfig filterConfig)
void	setMaxRequests(int value) Set the maximum number of requests allowed to be processed at the same time.
void	setSuspendMs(long value) Set the amount of time (in milliseconds) that the filter would suspend a request for while waiting for the semaphore to become available.
void	setWaitMs(long value) Set the (short) amount of time (in milliseconds) that the filter would wait for the semaphore to become available before suspending a request.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

_waitMs

protected long _waitMs

_suspendMs

protected long _suspendMs

_maxRequests

protected int _maxRequests

Constructor Detail

QoSFilter

public QoSFilter()

Method Detail

init

public void init(FilterConfig filterConfig)

Specified by:

init in interface Filter

See Also:

Filter.init(javax.servlet.FilterConfig)

doFilter

public void doFilter(ServletRequest request,
                     ServletResponse response,
                     FilterChain chain)
              throws IOException,
                     ServletException

Specified by:

doFilter in interface Filter

Throws:

IOException

ServletException

See Also:

Filter.doFilter(javax.servlet.ServletRequest, javax.servlet.ServletResponse, javax.servlet.FilterChain)

getPriority

protected int getPriority(ServletRequest request)

Get the request Priority.

The default implementation assigns the following priorities:

• 2 - for a authenticated request
• 1 - for a request with valid /non new session
• 0 - for all other requests.

This method may be specialised to provide application specific priorities.

Parameters:

request -

Returns:

the request priority

destroy

public void destroy()

Specified by:

destroy in interface Filter

See Also:

Filter.destroy()

getWaitMs

public long getWaitMs()

Get the (short) amount of time (in milliseconds) that the filter would wait for the semaphore to become available before suspending a request.

Returns:

wait time (in milliseconds)

setWaitMs

public void setWaitMs(long value)

Set the (short) amount of time (in milliseconds) that the filter would wait for the semaphore to become available before suspending a request.

Parameters:

value - wait time (in milliseconds)

getSuspendMs

public long getSuspendMs()

Get the amount of time (in milliseconds) that the filter would suspend a request for while waiting for the semaphore to become available.

Returns:

suspend time (in milliseconds)

setSuspendMs

public void setSuspendMs(long value)

Set the amount of time (in milliseconds) that the filter would suspend a request for while waiting for the semaphore to become available.

Parameters:

value - suspend time (in milliseconds)

getMaxRequests

public int getMaxRequests()

Get the maximum number of requests allowed to be processed at the same time.

Returns:

maximum number of requests

setMaxRequests

public void setMaxRequests(int value)

Set the maximum number of requests allowed to be processed at the same time.

Parameters:

value - the number of requests