@ManagedObject(value="Quality of Service Filter") public class QoSFilter extends java.lang.Object implements 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.
Modifier and Type | Class and Description |
---|---|
private class |
QoSFilter.QoSAsyncListener |
Modifier and Type | Field and Description |
---|---|
(package private) static int |
__DEFAULT_MAX_PRIORITY |
(package private) static int |
__DEFAULT_PASSES |
(package private) static long |
__DEFAULT_TIMEOUT_MS |
(package private) static int |
__DEFAULT_WAIT_MS |
private javax.servlet.AsyncListener[] |
_listeners |
private int |
_maxRequests |
private java.util.concurrent.Semaphore |
_passes |
private java.util.Queue<javax.servlet.AsyncContext>[] |
_queues |
private java.lang.String |
_resumed |
private java.lang.String |
_suspended |
private long |
_suspendMs |
private long |
_waitMs |
private static Logger |
LOG |
(package private) static java.lang.String |
MANAGED_ATTR_INIT_PARAM |
(package private) static java.lang.String |
MAX_PRIORITY_INIT_PARAM |
(package private) static java.lang.String |
MAX_REQUESTS_INIT_PARAM |
(package private) static java.lang.String |
MAX_WAIT_INIT_PARAM |
(package private) static java.lang.String |
SUSPEND_INIT_PARAM |
Constructor and Description |
---|
QoSFilter() |
Modifier and Type | Method and Description |
---|---|
void |
destroy() |
void |
doFilter(javax.servlet.ServletRequest request,
javax.servlet.ServletResponse response,
javax.servlet.FilterChain chain) |
int |
getMaxRequests()
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 |
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(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.
|
private static final Logger LOG
static final int __DEFAULT_MAX_PRIORITY
static final int __DEFAULT_PASSES
static final int __DEFAULT_WAIT_MS
static final long __DEFAULT_TIMEOUT_MS
static final java.lang.String MANAGED_ATTR_INIT_PARAM
static final java.lang.String MAX_REQUESTS_INIT_PARAM
static final java.lang.String MAX_PRIORITY_INIT_PARAM
static final java.lang.String MAX_WAIT_INIT_PARAM
static final java.lang.String SUSPEND_INIT_PARAM
private final java.lang.String _suspended
private final java.lang.String _resumed
private long _waitMs
private long _suspendMs
private int _maxRequests
private java.util.concurrent.Semaphore _passes
private java.util.Queue<javax.servlet.AsyncContext>[] _queues
private javax.servlet.AsyncListener[] _listeners
public void init(javax.servlet.FilterConfig filterConfig)
init
in interface javax.servlet.Filter
public void doFilter(javax.servlet.ServletRequest request, javax.servlet.ServletResponse response, javax.servlet.FilterChain chain) throws java.io.IOException, javax.servlet.ServletException
doFilter
in interface javax.servlet.Filter
java.io.IOException
javax.servlet.ServletException
protected int getPriority(javax.servlet.ServletRequest request)
The default implementation assigns the following priorities:
request
- the incoming requestpublic void destroy()
destroy
in interface javax.servlet.Filter
@ManagedAttribute(value="(short) amount of time filter will wait before suspending request (in ms)") public long getWaitMs()
public void setWaitMs(long value)
value
- wait time (in milliseconds)@ManagedAttribute(value="amount of time filter will suspend a request for while waiting for the semaphore to become available (in ms)") public long getSuspendMs()
public void setSuspendMs(long value)
value
- suspend time (in milliseconds)@ManagedAttribute(value="maximum number of requests to allow processing of at the same time") public int getMaxRequests()
public void setMaxRequests(int value)
value
- the number of requests