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Optional jitter for the cache ttl #107

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Optional jitter for the cache ttl #107

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20 changes: 20 additions & 0 deletions zio-cache/shared/src/main/scala/zio/cache/Cache.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -95,6 +95,26 @@ abstract class Cache[-Key, +Error, +Value] {
def size(implicit trace: Trace): UIO[Int]
}

object TimeToLive {

/**
* Returns a TTL function that adds randomized jitter to the base time to live.
*
* The `min` and `max` parameters control the bounds within which the base time to live
* is randomly scaled.
*/
def jittered[Value](
timeToLive: Exit[Nothing, Value] => Duration,
min: Double,
max: Double
): Exit[Nothing, Value] => Duration = { (exit: Exit[Nothing, Value]) =>
val d = timeToLive(exit).toNanos
val random = scala.util.Random.nextDouble()
val jittered = d * min * (1 - random) + d * max * random
zio.Duration.fromNanos(jittered.toLong)
}
}

object Cache {

/**
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21 changes: 20 additions & 1 deletion zio-cache/shared/src/test/scala/zio/cache/CacheSpec.scala
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Expand Up @@ -72,7 +72,26 @@ object CacheSpec extends ZIOSpecDefault {
expected <- ZIO.foreachPar(1 to 100)(hash(salt))
} yield assertTrue(actual == expected)
}
}
},
test("jitter") {
check(Gen.int(20, 100)) { duration =>
for {
ref <- Ref.make(0)
lookup = Lookup((n: Int) => ref.updateAndGet(_ + 1).as(n))
cache <- Cache.makeWith(10, lookup)(TimeToLive.jittered(_ => duration.seconds, 1, 2))
_ <- cache.get(1)
lookupCount1 <- ref.get
_ <- TestClock.adjust((duration / 10).seconds)
_ <- cache.get(1)
lookupCount2 <- ref.get
_ <- TestClock.adjust((duration * 2).seconds)
_ <- cache.get(1)
lookupCount3 <- ref.get
} yield assertTrue(
lookupCount1 == 1 && lookupCount2 == 1 && lookupCount3 == 2
)
}
} @@ TestAspect.samples(10)
),
suite("`refresh` method")(
test("should update the cache with a new value") {
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