Merge pull request #40 from alitto/bug/context-error

Return Context error if it is canceled before at least 1 task failed

.github/workflows/main.yml

@@ -34,7 +34,7 @@ jobs:
       uses: actions/checkout@v2
     - name: Test
       run: make coverage
-    - uses: codecov/codecov-action@v2
+    - uses: codecov/codecov-action@v3
       with:
         files: coverage.out
         fail_ci_if_error: true

group.go

@@ -50,26 +50,16 @@ func (g *TaskGroupWithContext) Submit(task func() error) {
 		defer g.waitGroup.Done()
 
 		// If context has already been cancelled, skip task execution
-		if g.ctx != nil {
-			select {
-			case <-g.ctx.Done():
-				return
-			default:
-			}
+		select {
+		case <-g.ctx.Done():
+			return
+		default:
 		}
 
 		// don't actually ignore errors
 		err := task()
 		if err != nil {
-			g.errSync.once.Do(func() {
-				g.errSync.guard.Lock()
-				g.err = err
-				g.errSync.guard.Unlock()
-
-				if g.cancel != nil {
-					g.cancel()
-				}
-			})
+			g.setError(err)
 		}
 	})
 }
@@ -91,11 +81,26 @@ func (g *TaskGroupWithContext) Wait() error {
 		// If context was provided, cancel it to signal all running tasks to stop
 		g.cancel()
 	case <-g.ctx.Done():
+		g.setError(g.ctx.Err())
 	}
 
+	return g.getError()
+}
+
+func (g *TaskGroupWithContext) getError() error {
 	g.errSync.guard.RLock()
 	err := g.err
 	g.errSync.guard.RUnlock()
-
 	return err
 }
+
+func (g *TaskGroupWithContext) setError(err error) {
+	g.errSync.once.Do(func() {
+		g.errSync.guard.Lock()
+		g.err = err
+		g.errSync.guard.Unlock()
+
+		// Cancel execution of any pending task in this group
+		g.cancel()
+	})
+}

group_blackbox_test.go

@@ -120,3 +120,34 @@ func TestGroupContextWithNilContext(t *testing.T) {
 
 	assertEqual(t, "a non-nil context needs to be specified when using GroupContext", thrownPanic)
 }
+
+func TestGroupContextWithCanceledContext(t *testing.T) {
+
+	pool := pond.New(3, 100)
+	assertEqual(t, 0, pool.RunningWorkers())
+
+	// Submit a group of tasks
+	var doneCount, startedCount int32
+	userCtx, cancel := context.WithCancel(context.Background())
+	group, ctx := pool.GroupContext(userCtx)
+	for i := 0; i < 10; i++ {
+		group.Submit(func() error {
+			atomic.AddInt32(&startedCount, 1)
+
+			select {
+			case <-time.After(10 * time.Millisecond):
+				atomic.AddInt32(&doneCount, 1)
+			case <-ctx.Done():
+			}
+
+			return nil
+		})
+	}
+
+	// Cancel context right after submitting tasks
+	cancel()
+
+	err := group.Wait()
+	assertEqual(t, context.Canceled, err)
+	assertEqual(t, int32(0), atomic.LoadInt32(&doneCount))
+}