From aabb3b82757b715876fafe4d7ffaced183c04fd6 Mon Sep 17 00:00:00 2001
From: Matthias Andreas Benkard <code@mail.matthias.benkard.de>
Date: Wed, 10 Jan 2018 20:46:29 +0100
Subject: Make Fiber.run stack-safe.

Previously, Fiber.run was implemented with non-tail recursion, which
would blow the stack after too many effects were invoked.  It is now a
stack-safe loop.
---
 core/lib/Fiber.scala | 71 +++++++++++++++++++++++++++++-----------------------
 1 file changed, 39 insertions(+), 32 deletions(-)

diff --git a/core/lib/Fiber.scala b/core/lib/Fiber.scala
index 0e2ef39..2d73f9e 100644
--- a/core/lib/Fiber.scala
+++ b/core/lib/Fiber.scala
@@ -131,39 +131,46 @@ object Fiber extends FiberConversions with FiberTypes {
     monix.reactive.Observable.create[Out](OverflowStrategy.Unbounded) { out ⇒
       val cancelable = SingleAssignmentCancelable()
 
-      def handle(more: (Effect[Out], Any ⇒ Any)): Unit = {
-        val (effect, continue) = more
-        try {
-          effect match {
-            case Effect.AwaitTask(task, scheduler) ⇒
-              task.asyncBoundary.runOnComplete({ result ⇒
-                val k = continue(result)
-                handle(k.asInstanceOf[(Effect[Out], Any ⇒ Any)])
-              })(scheduler)
-            case Effect.AwaitFuture(task, executionContext) ⇒
-              task.onComplete({ result ⇒
-                val k = continue(result)
-                handle(k.asInstanceOf[(Effect[Out], Any ⇒ Any)])
-              })(executionContext)
-            case Effect.GetFiberVar ⇒
-              val k = continue(state.fiberVar)
-              handle(k.asInstanceOf[(Effect[Out], Any ⇒ Any)])
-            case Effect.PutFiberVar(value) ⇒
-              state.fiberVar = value
-              val k = continue(())
-              handle(k.asInstanceOf[(Effect[Out], Any ⇒ Any)])
-            case Effect.Emit(returnValue) ⇒
-              out.onNext(returnValue.asInstanceOf[Out])
-              val k = continue(())
-              handle(k.asInstanceOf[(Effect[Out], Any ⇒ Any)])
-            case Effect.Fail(throwable) ⇒
-              out.onError(throwable)
-            case Effect.Finish ⇒
-              out.onComplete()
+      def handle(init: (Effect[Out], Any ⇒ Any)): Unit = {
+        var more = init
+        var done = false
+        while (!done) {
+          try {
+            val (effect, continue) = more
+            effect match {
+              case Effect.AwaitTask(task, scheduler) ⇒
+                task.asyncBoundary.runOnComplete({ result ⇒
+                  val k = continue(result)
+                  handle(k.asInstanceOf[(Effect[Out], Any ⇒ Any)])
+                })(scheduler)
+                done = true
+              case Effect.AwaitFuture(task, executionContext) ⇒
+                task.onComplete({ result ⇒
+                  val k = continue(result)
+                  handle(k.asInstanceOf[(Effect[Out], Any ⇒ Any)])
+                })(executionContext)
+                done = true
+              case Effect.GetFiberVar ⇒
+                more = continue(state.fiberVar)
+                  .asInstanceOf[(Effect[Out], Any ⇒ Any)]
+              case Effect.PutFiberVar(value) ⇒
+                state.fiberVar = value
+                more = continue(()).asInstanceOf[(Effect[Out], Any ⇒ Any)]
+              case Effect.Emit(returnValue) ⇒
+                out.onNext(returnValue.asInstanceOf[Out])
+                more = continue(()).asInstanceOf[(Effect[Out], Any ⇒ Any)]
+              case Effect.Fail(throwable) ⇒
+                out.onError(throwable)
+                done = true
+              case Effect.Finish ⇒
+                out.onComplete()
+                done = true
+            }
+          } catch {
+            case NonFatal(err) ⇒
+              out.onError(err)
+              done = true
           }
-        } catch {
-          case NonFatal(err) ⇒
-            out.onError(err)
         }
       }
 
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