Merge pull request #4214 from djspiewak/bug/broken-arm-block-detection

Fixed off-by-one error in other index selection
typelevel · Dec 27, 2024 · ead4b58 · ead4b58
2 parents 5e470b1 + bf77077
commit ead4b58
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diff --git a/core/jvm/src/main/scala/cats/effect/unsafe/WorkerThread.scala b/core/jvm/src/main/scala/cats/effect/unsafe/WorkerThread.scala
@@ -563,7 +563,7 @@ private[effect] final class WorkerThread[P <: AnyRef](
             // TODO check that branch elimination makes it free when off
             val idx = index
             val threadCount = pool.getWorkerThreadCount()
-            val otherIdx = (idx + random.nextInt(threadCount - 1)) % threadCount
+            val otherIdx = (idx + random.nextInt(threadCount - 1) + 1) % threadCount
             val thread = pool.getWorkerThread(otherIdx)
             val state = thread.getState()
             val parked = thread.parked

diff --git a/tests/jvm/src/main/scala/catseffect/examplesplatform.scala b/tests/jvm/src/main/scala/catseffect/examplesplatform.scala
@@ -76,8 +76,8 @@ package examples {
     override protected def blockedThreadDetectionEnabled = true
 
     // Loop prevents other worker threads from being parked and hence not
-    // performing the blocked check
+    // performing the blocked check. Cedeing makes the test more deterministic
     val run =
-      IO.unit.foreverM.start >> IO(Thread.sleep(2.seconds.toMillis))
+      IO.cede.foreverM.start >> IO(Thread.sleep(2.seconds.toMillis))
   }
 }