com.google.common.util.concurrent

Class SmoothRateLimiter.SmoothWarmingUp

java.lang.Object

com.google.common.util.concurrent.RateLimiter

com.google.common.util.concurrent.SmoothRateLimiter

com.google.common.util.concurrent.SmoothRateLimiter.SmoothWarmingUp

Enclosing class:

SmoothRateLimiter

static final class SmoothRateLimiter.SmoothWarmingUp
extends SmoothRateLimiter

This implements the following function where coldInterval = coldFactor * stableInterval. ^ throttling | cold + / interval | /. | / . | / . <-- "warmup period" is the area of the trapezoid between | / . thresholdPermits and maxPermits | / . | / . | / . stable +----------/ WARM . interval | . UP . | . PERIOD. | . . 0 +----------+-------+--------------> storedPermits 0 thresholdPermits maxPermits Before going into the details of this particular function, let's keep in mind the basics: 1) The state of the RateLimiter (storedPermits) is a vertical line in this figure. 2) When the RateLimiter is not used, this goes right (up to maxPermits) 3) When the RateLimiter is used, this goes left (down to zero), since if we have storedPermits, we serve from those first 4) When _unused_, we go right at a constant rate! The rate at which we move to the right is chosen as maxPermits / warmupPeriod. This ensures that the time it takes to go from 0 to maxPermits is equal to warmupPeriod. 5) When _used_, the time it takes, as explained in the introductory class note, is equal to the integral of our function, between X permits and X-K permits, assuming we want to spend K saved permits. In summary, the time it takes to move to the left (spend K permits), is equal to the area of the function of width == K. Assuming we have saturated demand, the time to go from maxPermits to thresholdPermits is equal to warmupPeriod. And the time to go from thresholdPermits to 0 is warmupPeriod/2. (The reason that this is warmupPeriod/2 is to maintain the behavior of the original implementation where coldFactor was hard coded as 3.) It remains to calculate thresholdsPermits and maxPermits. - The time to go from thresholdPermits to 0 is equal to the integral of the function between 0 and thresholdPermits. This is thresholdPermits * stableIntervals. By (5) it is also equal to warmupPeriod/2. Therefore thresholdPermits = 0.5 * warmupPeriod / stableInterval. - The time to go from maxPermits to thresholdPermits is equal to the integral of the function between thresholdPermits and maxPermits. This is the area of the pictured trapezoid, and it is equal to 0.5 * (stableInterval + coldInterval) * (maxPermits - thresholdPermits). It is also equal to warmupPeriod, so maxPermits = thresholdPermits + 2 * warmupPeriod / (stableInterval + coldInterval).

Nested Class Summary

Nested classes/interfaces inherited from class com.google.common.util.concurrent.SmoothRateLimiter

SmoothRateLimiter.SmoothBursty, SmoothRateLimiter.SmoothWarmingUp

Nested classes/interfaces inherited from class com.google.common.util.concurrent.RateLimiter

RateLimiter.SleepingStopwatch

Field Summary

Fields

Modifier and Type	Field and Description
private double	coldFactor
private double	slope The slope of the line from the stable interval (when permits == 0), to the cold interval (when permits == maxPermits)
private double	thresholdPermits
private long	warmupPeriodMicros

Fields inherited from class com.google.common.util.concurrent.SmoothRateLimiter

maxPermits, stableIntervalMicros, storedPermits

Constructor Summary

Constructors

Constructor and Description
SmoothWarmingUp(RateLimiter.SleepingStopwatch stopwatch, long warmupPeriod, java.util.concurrent.TimeUnit timeUnit, double coldFactor)

Method Summary

Modifier and Type	Method and Description
(package private) double	coolDownIntervalMicros() Returns the number of microseconds during cool down that we have to wait to get a new permit.
(package private) void	doSetRate(double permitsPerSecond, double stableIntervalMicros)
private double	permitsToTime(double permits)
(package private) long	storedPermitsToWaitTime(double storedPermits, double permitsToTake) Translates a specified portion of our currently stored permits which we want to spend/acquire, into a throttling time.

Methods inherited from class com.google.common.util.concurrent.SmoothRateLimiter

doGetRate, doSetRate, queryEarliestAvailable, reserveEarliestAvailable, resync

Methods inherited from class com.google.common.util.concurrent.RateLimiter

acquire, acquire, create, create, create, create, getRate, reserve, reserveAndGetWaitLength, setRate, toString, tryAcquire, tryAcquire, tryAcquire, tryAcquire

Methods inherited from class java.lang.Object

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

Field Detail

warmupPeriodMicros

private final long warmupPeriodMicros

slope

private double slope

The slope of the line from the stable interval (when permits == 0), to the cold interval (when permits == maxPermits)

thresholdPermits

private double thresholdPermits

coldFactor

private double coldFactor

Constructor Detail

SmoothWarmingUp

SmoothWarmingUp(RateLimiter.SleepingStopwatch stopwatch,
                long warmupPeriod,
                java.util.concurrent.TimeUnit timeUnit,
                double coldFactor)

Method Detail

doSetRate

void doSetRate(double permitsPerSecond,
               double stableIntervalMicros)

Specified by:

doSetRate in class SmoothRateLimiter

storedPermitsToWaitTime

long storedPermitsToWaitTime(double storedPermits,
                             double permitsToTake)

Description copied from class: SmoothRateLimiter

Translates a specified portion of our currently stored permits which we want to spend/acquire, into a throttling time. Conceptually, this evaluates the integral of the underlying function we use, for the range of [(storedPermits - permitsToTake), storedPermits].

This always holds: 0 <= permitsToTake <= storedPermits

Specified by:

storedPermitsToWaitTime in class SmoothRateLimiter

permitsToTime

private double permitsToTime(double permits)

coolDownIntervalMicros

double coolDownIntervalMicros()

Description copied from class: SmoothRateLimiter

Returns the number of microseconds during cool down that we have to wait to get a new permit.

Specified by:

coolDownIntervalMicros in class SmoothRateLimiter