From b6031ad05d9e766d5a29520ca0ecb1f38281a084 Mon Sep 17 00:00:00 2001
From: Isaac Levy <isaac.r.levy@gmail.com>
Date: Thu, 12 Sep 2024 14:26:09 -0400
Subject: [PATCH] Fix ThreadLocalRandom

Current impl was not creating thread local randoms!
---
 lila/src/main/scala/Random.scala     |  7 ++++++-
 lila/src/test/scala/RandomTest.scala | 12 ++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)
 create mode 100644 lila/src/test/scala/RandomTest.scala

diff --git a/lila/src/main/scala/Random.scala b/lila/src/main/scala/Random.scala
index 3ca0cea..dd61d60 100644
--- a/lila/src/main/scala/Random.scala
+++ b/lila/src/main/scala/Random.scala
@@ -2,7 +2,12 @@ package scalalib
 
 import scala.collection.mutable.StringBuilder
 
-val ThreadLocalRandom = RandomApi(java.util.concurrent.ThreadLocalRandom.current)
+import scala.collection.mutable.StringBuilder
+
+private final val store =
+  java.lang.ThreadLocal.withInitial(() => RandomApi(java.util.concurrent.ThreadLocalRandom.current))
+
+def ThreadLocalRandom = store.get
 
 val SecureRandom = RandomApi(java.security.SecureRandom())
 
diff --git a/lila/src/test/scala/RandomTest.scala b/lila/src/test/scala/RandomTest.scala
new file mode 100644
index 0000000..2b2095d
--- /dev/null
+++ b/lila/src/test/scala/RandomTest.scala
@@ -0,0 +1,12 @@
+package scalalib
+
+class RandomTest extends munit.FunSuite:
+
+  test("different threads get different randoms"):
+    val r1 = ThreadLocalRandom
+
+    @volatile var r2: RandomApi = null
+    val thread2                 = new Thread(() => r2 = ThreadLocalRandom)
+    thread2.start()
+    thread2.join()
+    assertNotEquals(r1, r2)