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java.lang.Object org.eclipse.jetty.servlets.QoSFilter
public class QoSFilter
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 | |
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protected int |
_maxRequests
|
protected long |
_suspendMs
|
protected long |
_waitMs
|
Constructor Summary | |
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QoSFilter()
|
Method Summary | |
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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 |
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protected long _waitMs
protected long _suspendMs
protected int _maxRequests
Constructor Detail |
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public QoSFilter()
Method Detail |
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public void init(FilterConfig filterConfig)
init
in interface Filter
Filter.init(javax.servlet.FilterConfig)
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException
doFilter
in interface Filter
IOException
ServletException
Filter.doFilter(javax.servlet.ServletRequest, javax.servlet.ServletResponse, javax.servlet.FilterChain)
protected int getPriority(ServletRequest request)
The default implementation assigns the following priorities:
request
-
public void destroy()
destroy
in interface Filter
Filter.destroy()
public long getWaitMs()
public void setWaitMs(long value)
value
- wait time (in milliseconds)public long getSuspendMs()
public void setSuspendMs(long value)
value
- suspend time (in milliseconds)public int getMaxRequests()
public void setMaxRequests(int value)
value
- the number of requests
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