From 6c25dd3c0ddda2ce8f9e110c5f7a80825e05f314 Mon Sep 17 00:00:00 2001
From: Keith Zantow <kzantow@gmail.com>
Date: Tue, 20 May 2025 17:54:15 -0400
Subject: [PATCH] feat: Parallel function

Signed-off-by: Keith Zantow <kzantow@gmail.com>
---
 parallel.go      |  9 ++++++
 parallel_test.go | 75 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 84 insertions(+)
 create mode 100644 parallel.go
 create mode 100644 parallel_test.go

diff --git a/parallel.go b/parallel.go
new file mode 100644
index 0000000..d4c92ef
--- /dev/null
+++ b/parallel.go
@@ -0,0 +1,9 @@
+package sync
+
+import "context"
+
+func Parallel(ctx *context.Context, executorName string, funcs ...func() error) error {
+	return Collect[func() error, struct{}](ctx, executorName, ToSeq(funcs), func(f func() error) (struct{}, error) {
+		return struct{}{}, f()
+	}, nil)
+}
diff --git a/parallel_test.go b/parallel_test.go
new file mode 100644
index 0000000..c28ca1a
--- /dev/null
+++ b/parallel_test.go
@@ -0,0 +1,75 @@
+package sync
+
+import (
+	"context"
+	"fmt"
+	"sync"
+	"sync/atomic"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func Test_Parallel(t *testing.T) {
+	count := atomic.Int32{}
+	count.Store(0)
+
+	wg1 := sync.WaitGroup{}
+	wg1.Add(1)
+
+	wg2 := sync.WaitGroup{}
+	wg2.Add(1)
+
+	wg3 := sync.WaitGroup{}
+	wg3.Add(1)
+
+	err1 := fmt.Errorf("error-1")
+	err2 := fmt.Errorf("error-2")
+	err3 := fmt.Errorf("error-3")
+
+	order := ""
+
+	c := SetContextExecutor(context.TODO(), ExecutorDefault, NewExecutor(-1))
+
+	got := Parallel(
+		&c,
+		"",
+		func() error {
+			wg1.Wait()
+			count.Add(1)
+			order = order + "_0"
+			return nil
+		},
+		func() error {
+			wg3.Wait()
+			defer wg2.Done()
+			count.Add(10)
+			order = order + "_1"
+			return err1
+		},
+		func() error {
+			wg2.Wait()
+			defer wg1.Done()
+			count.Add(100)
+			order = order + "_2"
+			return err2
+		},
+		func() error {
+			defer wg3.Done()
+			count.Add(1000)
+			order = order + "_3"
+			return err3
+		},
+	)
+	require.Equal(t, int32(1111), count.Load())
+	require.Equal(t, "_3_1_2_0", order)
+
+	errs := got.(interface{ Unwrap() []error }).Unwrap()
+
+	// cannot check equality to a slice with err1,2,3 because the functions above are running in parallel, for example:
+	// after func()#4 returns and the `wg3.Done()` has executed, the thread could immediately pause
+	// and the remaining functions execute first and err3 becomes the last in the list instead of the first
+	require.Contains(t, errs, err1)
+	require.Contains(t, errs, err2)
+	require.Contains(t, errs, err3)
+}