From e075e4026df491b68648c262c9a43eef3974b5bc Mon Sep 17 00:00:00 2001
From: Roger Schildmeijer <roger@spotify.com>
Date: Thu, 5 Nov 2020 11:46:16 +0100
Subject: [PATCH] Add support for CompletionStage<Void> tasks in the
 ConcurrencyReducer

---
 .../java/com/spotify/futures/ConcurrencyReducer.java   |  6 +++---
 .../com/spotify/futures/ConcurrencyReducerTest.java    | 10 ++++++++++
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/src/main/java/com/spotify/futures/ConcurrencyReducer.java b/src/main/java/com/spotify/futures/ConcurrencyReducer.java
index 81d3189..e8383a7 100644
--- a/src/main/java/com/spotify/futures/ConcurrencyReducer.java
+++ b/src/main/java/com/spotify/futures/ConcurrencyReducer.java
@@ -164,13 +164,13 @@ private void invoke(final CompletableFuture<T> response,
 
     future.whenComplete(
         (result, t) -> {
-          if (result != null) {
+          if (t != null) {
             limit.release();
-            response.complete(result);
+            response.completeExceptionally(t);
             pump();
           } else {
             limit.release();
-            response.completeExceptionally(t);
+            response.complete(result);
             pump();
           }
         });
diff --git a/src/test/java/com/spotify/futures/ConcurrencyReducerTest.java b/src/test/java/com/spotify/futures/ConcurrencyReducerTest.java
index 3219725..db11b83 100644
--- a/src/test/java/com/spotify/futures/ConcurrencyReducerTest.java
+++ b/src/test/java/com/spotify/futures/ConcurrencyReducerTest.java
@@ -54,6 +54,16 @@ public void testNullJob() throws Exception {
     limiter.add(null);
   }
 
+  @Test()
+  public void testVoidJob() {
+    final ConcurrencyReducer<Void> limiter = ConcurrencyReducer.create(1, 10);
+    final CompletionStage<Void> task = CompletableFuture.completedFuture(null);
+    assertTrue(task.toCompletableFuture().isDone());
+
+    final CompletableFuture<Void> stage = limiter.add(() -> task);
+    assertTrue(stage.isDone());
+  }
+
   @Test
   public void testJobReturnsNull() throws Exception {
     final ConcurrencyReducer<String> limiter = ConcurrencyReducer.create(1, 10);