Replace FilesInParallel with an errgroup.Group

internal/repository/worker_group.go

@@ -0,0 +1,35 @@
+package repository
+
+import (
+	"context"
+
+	"golang.org/x/sync/errgroup"
+)
+
+// RunWorkers runs count instances of workerFunc using an errgroup.Group.
+// After all workers have terminated, finalFunc is run. If an error occurs in
+// one of the workers, it is returned. FinalFunc is always run, regardless of
+// any other previous errors.
+func RunWorkers(ctx context.Context, count int, workerFunc, finalFunc func() error) error {
+	wg, ctx := errgroup.WithContext(ctx)
+
+	// run workers
+	for i := 0; i < count; i++ {
+		wg.Go(workerFunc)
+	}
+
+	// wait for termination
+	err := wg.Wait()
+
+	// make sure finalFunc is run
+	finalErr := finalFunc()
+
+	// if the workers returned an error, return it to the caller (disregarding
+	// any error from finalFunc)
+	if err != nil {
+		return err
+	}
+
+	// if not, return the value finalFunc returned
+	return finalErr
+}