suspend effects (#3444)

core-tests/shared/src/test/scala/zio/ZIOSpec.scala

@@ -256,6 +256,15 @@ object ZIOSpec extends ZIOBaseSpec {
         val list = List(1, 2, 3).map(IO.effectTotal[Int](_))
         val res  = IO.collectAllPar(list)
         assertM(res)(equalTo(List(1, 2, 3)))
+      },
+      testM("is referentially transparent") {
+        for {
+          counter <- Ref.make(0)
+          op      = counter.getAndUpdate(_ + 1)
+          ops3    = ZIO.collectAllPar(List(op, op, op))
+          ops6    = ops3.zipPar(ops3)
+          res     <- ops6
+        } yield assert(res._1)(not(equalTo(res._2)))
       }
     ),
     suite("collectAllParN")(

core/shared/src/main/scala/zio/ZIO.scala

@@ -16,8 +16,6 @@
 
 package zio
 
-import java.util.concurrent.atomic.AtomicReferenceArray
-
 import scala.concurrent.ExecutionContext
 import scala.reflect.ClassTag
 import scala.util.{ Failure, Success }
@@ -2588,17 +2586,17 @@ object ZIO extends ZIOCompanionPlatformSpecific {
    *
    * For a sequential version of this method, see `foreach`.
    */
-  def foreachPar[R, E, A, B](as: Iterable[A])(fn: A => ZIO[R, E, B]): ZIO[R, E, List[B]] = {
-    val size      = as.size
-    val resultArr = new AtomicReferenceArray[B](size)
-
-    val wrappedFn: ZIOFn1[(A, Int), ZIO[R, E, Any]] = ZIOFn(fn) {
-      case (a, i) => fn(a).tap(b => ZIO.effectTotal(resultArr.set(i, b)))
+  def foreachPar[R, E, A, B](as: Iterable[A])(f: A => ZIO[R, E, B]): ZIO[R, E, List[B]] = {
+    val size = as.size
+    effectTotal(Array.ofDim[AnyRef](size)).flatMap { array =>
+      val zioFunction: ZIOFn1[(A, Int), ZIO[R, E, Any]] =
+        ZIOFn(f) {
+          case (a, i) =>
+            f(a).flatMap(b => effectTotal(array(i) = b.asInstanceOf[AnyRef]))
+        }
+      foreachPar_(as.zipWithIndex)(zioFunction) *>
+        effectTotal(array.asInstanceOf[Array[B]].toList)
     }
-
-    foreachPar_(as.zipWithIndex)(wrappedFn).as(
-      (0 until size).reverse.foldLeft[List[B]](Nil)((acc, i) => resultArr.get(i) :: acc)
-    )
   }
 
   /**