added randomizer to retries

rbcs-client/src/main/kotlin/net/woggioni/rbcs/client/Client.kt

@@ -45,9 +45,9 @@ import java.time.Duration
 import java.util.Base64
 import java.util.concurrent.CompletableFuture
 import java.util.concurrent.atomic.AtomicInteger
+import kotlin.random.Random
 import io.netty.util.concurrent.Future as NettyFuture
 
-
 class RemoteBuildCacheClient(private val profile: Configuration.Profile) : AutoCloseable {
     private val group: NioEventLoopGroup
     private var sslContext: SslContext
@@ -206,6 +206,7 @@ class RemoteBuildCacheClient(private val profile: Configuration.Profile) : AutoC
                 retryPolicy.initialDelayMillis.toDouble(),
                 retryPolicy.exp,
                 outcomeHandler,
+                Random.Default,
                 operation
             )
         } else {

rbcs-client/src/main/kotlin/net/woggioni/rbcs/client/retry.kt

@@ -3,6 +3,8 @@ package net.woggioni.rbcs.client
 import io.netty.util.concurrent.EventExecutorGroup
 import java.util.concurrent.CompletableFuture
 import java.util.concurrent.TimeUnit
+import kotlin.math.pow
+import kotlin.random.Random
 
 sealed class OperationOutcome<T> {
     class Success<T>(val result: T) : OperationOutcome<T>()
@@ -24,8 +26,10 @@ fun <T> executeWithRetry(
     initialDelay: Double,
     exp: Double,
     outcomeHandler: OutcomeHandler<T>,
+    randomizer : Random?,
     cb: () -> CompletableFuture<T>
 ): CompletableFuture<T> {
+
     val finalResult = cb()
     var future = finalResult
     var shortCircuit = false
@@ -46,7 +50,7 @@ fun <T> executeWithRetry(
                     is OutcomeHandlerResult.Retry -> {
                         val res = CompletableFuture<T>()
                         val delay = run {
-                            val scheduledDelay = (initialDelay * Math.pow(exp, i.toDouble())).toLong()
+                            val scheduledDelay = (initialDelay * exp.pow(i.toDouble()) * (1.0 + (randomizer?.nextDouble(-0.5, 0.5) ?: 0.0))).toLong()
                             outcomeHandlerResult.suggestedDelayMillis?.coerceAtMost(scheduledDelay) ?: scheduledDelay
                         }
                         eventExecutorGroup.schedule({

rbcs-client/src/test/kotlin/net/woggioni/rbcs/client/RetryTest.kt

@@ -89,7 +89,7 @@ class RetryTest {
         val random = Random(testArgs.seed)
 
         val future =
-            executeWithRetry(executor, testArgs.maxAttempt, testArgs.initialDelay, testArgs.exp, outcomeHandler) {
+            executeWithRetry(executor, testArgs.maxAttempt, testArgs.initialDelay, testArgs.exp, outcomeHandler, null) {
                 val now = System.nanoTime()
                 val result = CompletableFuture<Int>()
                 executor.submit {
@@ -129,7 +129,7 @@ class RetryTest {
                     previousAttempt.first + testArgs.initialDelay * Math.pow(testArgs.exp, index.toDouble()) * 1e6
                 val actualTimestamp = timestamp
                 val err = Math.abs(expectedTimestamp - actualTimestamp) / expectedTimestamp
-                Assertions.assertTrue(err < 1e-3)
+                Assertions.assertTrue(err < 1e-2)
             }
             if (index == attempts.size - 1 && index < testArgs.maxAttempt - 1) {
                 /*