feat: Use Weilbull distribution for failures

1 files changed, 14 insertions, 5 deletions

diff --git a/opendc/opendc-core/src/main/kotlin/com/atlarge/opendc/core/failure/UncorrelatedFaultInjector.kt b/opendc/opendc-core/src/main/kotlin/com/atlarge/opendc/core/failure/UncorrelatedFaultInjector.kt
index 5155a25a..56706824 100644
--- a/opendc/opendc-core/src/main/kotlin/com/atlarge/opendc/core/failure/UncorrelatedFaultInjector.kt
+++ b/opendc/opendc-core/src/main/kotlin/com/atlarge/opendc/core/failure/UncorrelatedFaultInjector.kt
@@ -24,26 +24,35 @@
 
 package com.atlarge.opendc.core.failure
 
+import com.atlarge.odcsim.simulationContext
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.launch
-import kotlin.math.ln
+import kotlin.math.ln1p
+import kotlin.math.pow
 import kotlin.random.Random
 
 /**
  * A [FaultInjector] that injects uncorrelated faults into the system, meaning that failures of the subsystems are
  * independent.
  */
-public class UncorrelatedFaultInjector(private val mu: Double = 1024.0, private val random: Random = Random.Default) : FaultInjector {
+public class UncorrelatedFaultInjector(private val alpha: Double, private val beta: Double, private val random: Random = Random) : FaultInjector {
     /**
      * Enqueue the specified [FailureDomain] to fail some time in the future.
      */
     override fun enqueue(domain: FailureDomain) {
         domain.scope.launch {
-            val d = random.expovariate(mu)
-            delay(d)
+            val d = random.weibull(alpha, beta) * 1e3 // Make sure to convert delay to milliseconds
+            
+            // Handle long overflow
+            if (simulationContext.clock.millis() + d <= 0) {
+                return@launch
+            }
+
+            delay(d.toLong())
             domain.fail()
         }
     }
 
-    private fun Random.expovariate(mu: Double) = (-mu * ln(1 - nextDouble())).toLong()
+    // XXX We should extract this in some common package later on.
+    private fun Random.weibull(alpha: Double, beta: Double) = (beta * (-ln1p(-nextDouble())).pow(1.0 / alpha))
 }