concurrency/joino (#139)

`Join` runs multiple Runners concurrently and waits for all of them to
complete. It returns a combined error if any of the Runners return an
error. It does not cancel the context if one of the Runners fails; all
Runners are allowed to complete.

Signed-off-by: joshvanl <[email protected]>

Author: JoshVanL

concurrency/join.go

@@ -0,0 +1,39 @@
+/*
+Copyright 2025 The Dapr Authors
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+    http://www.apache.org/licenses/LICENSE-2.0
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package concurrency
+
+import (
+	"context"
+	"errors"
+	"sync"
+)
+
+// Join runs multiple Runners concurrently and waits for all of them to
+// complete. It returns a combined error if any of the Runners return an error.
+// It does not cancel the context if one of the Runners fails; all Runners are
+// allowed to complete.
+func Join(ctx context.Context, runners ...Runner) error {
+	errs := make([]error, len(runners))
+	var wg sync.WaitGroup
+	wg.Add(len(runners))
+	for i := range runners {
+		go func(i int) {
+			errs[i] = runners[i](ctx)
+			wg.Done()
+		}(i)
+	}
+	wg.Wait()
+
+	return errors.Join(errs...)
+}