Class QoSFilter
- All Implemented Interfaces:
javax.servlet.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.
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Nested Class Summary
Nested Classes -
Field Summary
FieldsModifier and TypeFieldDescriptionprivate javax.servlet.AsyncListener[]
private int
private Semaphore
private Queue<javax.servlet.AsyncContext>[]
private final String
private final String
private long
private long
(package private) static final int
(package private) static final int
(package private) static final long
(package private) static final int
private static final Logger
(package private) static final String
(package private) static final String
(package private) static final String
(package private) static final String
(package private) static final String
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionvoid
destroy()
void
doFilter
(javax.servlet.ServletRequest request, javax.servlet.ServletResponse response, javax.servlet.FilterChain chain) int
Get the maximum number of requests allowed to be processed at the same time.protected int
getPriority
(javax.servlet.ServletRequest request) Computes the request priority.long
Get the amount of time (in milliseconds) that the filter would suspend a request for while waiting for the semaphore to become available.long
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
(javax.servlet.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.
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Field Details
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LOG
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DEFAULT_MAX_PRIORITY
static final int DEFAULT_MAX_PRIORITY- See Also:
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DEFAULT_PASSES
static final int DEFAULT_PASSES- See Also:
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DEFAULT_WAIT_MS
static final int DEFAULT_WAIT_MS- See Also:
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DEFAULT_TIMEOUT_MS
static final long DEFAULT_TIMEOUT_MS- See Also:
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MANAGED_ATTR_INIT_PARAM
- See Also:
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MAX_REQUESTS_INIT_PARAM
- See Also:
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MAX_PRIORITY_INIT_PARAM
- See Also:
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MAX_WAIT_INIT_PARAM
- See Also:
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SUSPEND_INIT_PARAM
- See Also:
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_suspended
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_resumed
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_waitMs
private long _waitMs -
_suspendMs
private long _suspendMs -
_maxRequests
private int _maxRequests -
_passes
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_queues
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_listeners
private javax.servlet.AsyncListener[] _listeners
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Constructor Details
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QoSFilter
public QoSFilter()
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Method Details
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init
public void init(javax.servlet.FilterConfig filterConfig) - Specified by:
init
in interfacejavax.servlet.Filter
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doFilter
public void doFilter(javax.servlet.ServletRequest request, javax.servlet.ServletResponse response, javax.servlet.FilterChain chain) throws IOException, javax.servlet.ServletException - Specified by:
doFilter
in interfacejavax.servlet.Filter
- Throws:
IOException
javax.servlet.ServletException
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getPriority
protected int getPriority(javax.servlet.ServletRequest request) Computes the request priority.The default implementation assigns the following priorities:
- 2 - for an authenticated request
- 1 - for a request with valid / non new session
- 0 - for all other requests.
- Parameters:
request
- the incoming request- Returns:
- the computed request priority
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destroy
public void destroy()- Specified by:
destroy
in interfacejavax.servlet.Filter
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getWaitMs
@ManagedAttribute("(short) amount of time filter will wait before suspending request (in ms)") 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)
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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)
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getSuspendMs
@ManagedAttribute("amount of time filter will suspend a request for while waiting for the semaphore to become available (in ms)") 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)
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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)
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getMaxRequests
@ManagedAttribute("maximum number of requests to allow processing of at the same time") public int getMaxRequests()Get the maximum number of requests allowed to be processed at the same time.- Returns:
- maximum number of requests
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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
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