org.apache.catalina.util

Class TimeBucketCounter

java.lang.Object

org.apache.catalina.util.TimeBucketCounter

public class TimeBucketCounter
extends java.lang.Object

This class maintains a thread safe hash map that has timestamp-based buckets followed by a string for a key, and a counter for a value. each time the increment() method is called it adds the key if it does not exist, increments its value and returns it. a maintenance thread cleans up keys that are prefixed by previous timestamp buckets.

Constructor Summary

Constructors

Constructor and Description
TimeBucketCounter(int bucketDuration, java.util.concurrent.ScheduledExecutorService executorService) Creates a new TimeBucketCounter with the specified lifetime.

Method Summary

Modifier and Type	Method and Description
void	destroy() Sets isRunning to false to terminate the maintenance thread.
int	getActualDuration() The actual duration may differ from the configured duration because it is set to the next power of 2 value in order to perform very fast bit shift arithmetic.
int	getCurrentBucketPrefix() Calculates the current time bucket prefix by shifting bits for fast division, e.g. shift 16 bits is the same as dividing by 65,536 which is about 1:05m.
long	getMillisUntilNextBucket() When we want to test a full bucket duration we need to sleep until the next bucket starts.
int	getNumBits()
double	getRatio() Returns the ratio between the configured duration param and the actual duration which will be set to the next power of 2.
int	increment(java.lang.String identifier) Increments the counter for the passed identifier in the current time bucket and returns the new value.

Methods inherited from class java.lang.Object

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

Constructor Detail

TimeBucketCounter

public TimeBucketCounter(int bucketDuration,
                         java.util.concurrent.ScheduledExecutorService executorService)

Creates a new TimeBucketCounter with the specified lifetime.

Parameters:

bucketDuration - duration in seconds, e.g. for 1 minute pass 60

executorService - the executor service which will be used to run the maintenance

Method Detail

increment

public final int increment(java.lang.String identifier)

Increments the counter for the passed identifier in the current time bucket and returns the new value.

Parameters:

identifier - an identifier for which we want to maintain count, e.g. IP Address

Returns:

the count within the current time bucket

getCurrentBucketPrefix

public final int getCurrentBucketPrefix()

Calculates the current time bucket prefix by shifting bits for fast division, e.g. shift 16 bits is the same as dividing by 65,536 which is about 1:05m.

Returns:

The current bucket prefix.

getNumBits

public int getNumBits()

getActualDuration

public int getActualDuration()

The actual duration may differ from the configured duration because it is set to the next power of 2 value in order to perform very fast bit shift arithmetic.

Returns:

the actual bucket duration in milliseconds

getRatio

public double getRatio()

Returns the ratio between the configured duration param and the actual duration which will be set to the next power of 2. We then multiply the configured requests param by the same ratio in order to compensate for the added time, if any.

Returns:

the ratio, e.g. 1.092 if the actual duration is 65_536 for the configured duration of 60_000

getMillisUntilNextBucket

public long getMillisUntilNextBucket()

When we want to test a full bucket duration we need to sleep until the next bucket starts.

Returns:

the number of milliseconds until the next bucket

destroy

public void destroy()

Sets isRunning to false to terminate the maintenance thread.