Fix a bug that could leave the coroutine scheduler's PRNG in an inval…

…id state (Kotlin#4052)

A potential bug is fixed, where `nextInt` would always return zero due to incorrect initialization of rngState with zero.
This could happen during the creation of a worker with thread id = `1595972770` (JDK >=8), or unpredictable if fallback thread-local random is used (android SDK <34 or JDK <7), approximate probability is 2.4E-10

Also, this slightly optimizes the performance of coroutines initialization. During the creation of `CoroutineScheduler.Worker`, we need to initialize its embedded random number generator.
To avoid additional class-loading costs (Kotlin#4051), `rngState` is now directly initialized from the current nanoTime (that is used as seed).

Fixes Kotlin#4051

Co-authored-by: Vsevolod Tolstopyatov <[email protected]>

kotlinx-coroutines-core/jvm/src/scheduling/CoroutineScheduler.kt

@@ -8,7 +8,6 @@ import java.util.concurrent.*
 import java.util.concurrent.locks.*
 import kotlin.jvm.internal.Ref.ObjectRef
 import kotlin.math.*
-import kotlin.random.*
 
 /**
  * Coroutine scheduler (pool of shared threads) which primary target is to distribute dispatched coroutines
@@ -658,11 +657,21 @@ internal class CoroutineScheduler(
         var nextParkedWorker: Any? = NOT_IN_STACK
 
         /*
-         * The delay until at least one task in other worker queues will  become stealable.
+         * The delay until at least one task in other worker queues will become stealable.
          */
         private var minDelayUntilStealableTaskNs = 0L
 
-        private var rngState = Random.nextInt()
+        /**
+         * The state of embedded Marsaglia xorshift random number generator, used for work-stealing purposes.
+         * It is initialized with a seed.
+         */
+        private var rngState: Int = run {
+            // This could've been Random.nextInt(), but we are shaving an extra initialization cost, see #4051
+            val seed = System.nanoTime().toInt()
+            // rngState shouldn't be zero, as required for the xorshift algorithm
+            if (seed != 0) return@run seed
+            42
+        }
 
         /**
          * Tries to acquire CPU token if worker doesn't have one