ParAff applicative should abort on uncaught exception (#135)

* ParAff applicative should abort on uncaught exception

* Test parallel/throw with never

Author: natefaubion

src/Control/Monad/Aff.js

@@ -19,7 +19,7 @@ var Aff = function () {
     | Async ((Either Error a -> Eff eff Unit) -> Eff eff (Canceler eff))
     | forall b. Bind (Aff eff b) (b -> Aff eff a)
     | forall b. Bracket (Aff eff b) (BracketConditions eff b) (b -> Aff eff a)
-    | forall b. Fork Boolean (Aff eff b) ?(Thread eff b -> a)
+    | forall b. Fork Boolean (Aff eff b) ?(Fiber eff b -> a)
     | Sequential (ParAff aff a)
 
   */
@@ -762,26 +762,33 @@ var Aff = function () {
         case APPLY:
           lhs = head._1._3;
           rhs = head._2._3;
-          // We can only proceed if both sides have resolved.
-          if (lhs === EMPTY || rhs === EMPTY) {
-            return;
-          }
-          // If either side resolve with an error, we should continue with
-          // the first error.
-          if (util.isLeft(lhs)) {
-            if (util.isLeft(rhs)) {
-              if (fail === lhs) {
-                fail = rhs;
-              }
-            } else {
-              fail = lhs;
-            }
-            step    = null;
-            head._3 = fail;
-          } else if (util.isLeft(rhs)) {
-            step    = null;
-            fail    = rhs;
+          // If we have a failure we should kill the other side because we
+          // can't possible yield a result anymore.
+          if (fail) {
             head._3 = fail;
+            tmp     = true;
+            kid     = killId++;
+
+            kills[kid] = kill(early, fail === lhs ? head._2 : head._1, function (/* unused */) {
+              return function () {
+                delete kills[kid];
+                if (tmp) {
+                  tmp = false;
+                } else if (tail === null) {
+                  join(step, null, null);
+                } else {
+                  join(step, tail._1, tail._2);
+                }
+              };
+            });
+
+            if (tmp) {
+              tmp = false;
+              return;
+            }
+          } else if (lhs === EMPTY || rhs === EMPTY) {
+            // We can only proceed if both sides have resolved.
+            return;
           } else {
             step    = util.right(util.fromRight(lhs)(util.fromRight(rhs)));
             head._3 = step;

test/Test/Main.purs

@@ -19,7 +19,7 @@ import Control.Monad.Error.Class (throwError, catchError)
 import Control.Parallel (parallel, sequential, parTraverse_)
 import Data.Array as Array
 import Data.Bifunctor (lmap)
-import Data.Either (Either(..), isLeft, isRight)
+import Data.Either (Either(..), either, isLeft, isRight)
 import Data.Foldable (sum)
 import Data.Maybe (Maybe(..))
 import Data.Monoid (mempty)
@@ -64,6 +64,11 @@ assertEq s a aff = liftEff <<< assertEff s <<< map (eq a) =<< try aff
 assert ∷ ∀ eff. String → TestAff eff Boolean → TestAff eff Unit
 assert s aff = liftEff <<< assertEff s =<< try aff
 
+withTimeout ∷ ∀ eff a. Milliseconds → TestAff eff a → TestAff eff a
+withTimeout ms aff =
+  either throwError pure =<< sequential do
+    parallel (try aff) <|> parallel (delay ms $> Left (error "Timed out"))
+
 test_pure ∷ ∀ eff. TestEff eff Unit
 test_pure = runAssertEq "pure" 42 (pure 42)
 
@@ -411,6 +416,21 @@ test_parallel = assert "parallel" do
   r2 ← joinFiber f1
   pure (r1 == "foobar" && r2.a == "foo" && r2.b == "bar")
 
+test_parallel_throw ∷ ∀ eff. TestAff eff Unit
+test_parallel_throw = assert "parallel/throw" $ withTimeout (Milliseconds 100.0) do
+  ref ← newRef ""
+  let
+    action n s = do
+      delay (Milliseconds n)
+      modifyRef ref (_ <> s)
+      pure s
+  r1 ← try $ sequential $
+    { a: _, b: _ }
+      <$> parallel (action 10.0 "foo" *> throwError (error "Nope"))
+      <*> parallel never
+  r2 ← readRef ref
+  pure (isLeft r1 && r2 == "foo")
+
 test_kill_parallel ∷ ∀ eff. TestAff eff Unit
 test_kill_parallel = assert "kill/parallel" do
   ref ← newRef ""
@@ -641,6 +661,7 @@ main = do
     test_kill_finalizer_catch
     test_kill_finalizer_bracket
     test_parallel
+    test_parallel_throw
     test_kill_parallel
     test_parallel_alt
     test_parallel_alt_throw