From d112f7148eae9666fecbcd14d8dfdce1c3071121 Mon Sep 17 00:00:00 2001
From: Vasiliy Tolstov <v.tolstov@unistack.org>
Date: Sat, 9 Mar 2024 20:00:12 +0300
Subject: [PATCH] sync/waitgroup: initial implementation

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>
---
 sync/waitgroup.go      | 73 ++++++++++++++++++++++++++++++++++++++++++
 sync/waitgroup_test.go | 16 +++++++++
 2 files changed, 89 insertions(+)
 create mode 100644 sync/waitgroup.go
 create mode 100644 sync/waitgroup_test.go

diff --git a/sync/waitgroup.go b/sync/waitgroup.go
new file mode 100644
index 00000000..c417104e
--- /dev/null
+++ b/sync/waitgroup.go
@@ -0,0 +1,73 @@
+package sync
+
+import (
+	"context"
+	"sync"
+	"sync/atomic"
+)
+
+type WaitGroup struct {
+	wg    *sync.WaitGroup
+	drain *atomic.Bool
+	c     *atomic.Int64
+}
+
+func WrapWaitGroup(wg *sync.WaitGroup) *WaitGroup {
+	g := &WaitGroup{
+		wg:    wg,
+		c:     &(atomic.Int64{}),
+		drain: &(atomic.Bool{}),
+	}
+	return g
+}
+
+func NewWaitGroup() *WaitGroup {
+	var wg sync.WaitGroup
+	g := &WaitGroup{
+		wg:    &wg,
+		c:     &(atomic.Int64{}),
+		drain: &(atomic.Bool{}),
+	}
+	return g
+}
+
+func (g *WaitGroup) Add(n int) {
+	g.c.Add(int64(n))
+	g.wg.Add(n)
+}
+
+func (g *WaitGroup) Done() {
+	if g.drain.Load() {
+		return
+	}
+	g.c.Add(int64(-1))
+	g.wg.Done()
+}
+
+func (g *WaitGroup) Wait() {
+	g.wg.Wait()
+}
+
+func (g *WaitGroup) WaitContext(ctx context.Context) {
+	done := make(chan struct{})
+	go func() {
+		g.wg.Wait()
+		close(done)
+	}()
+
+	select {
+	case <-ctx.Done():
+		g.drain.Swap(true)
+		for g.c.Load() > 0 {
+			select {
+			case <-done:
+				g.drain.Swap(false)
+				return
+			default:
+				g.wg.Done()
+			}
+		}
+	case <-done:
+		return
+	}
+}
diff --git a/sync/waitgroup_test.go b/sync/waitgroup_test.go
new file mode 100644
index 00000000..67b1ca5b
--- /dev/null
+++ b/sync/waitgroup_test.go
@@ -0,0 +1,16 @@
+package sync
+
+import (
+	"context"
+	"testing"
+	"time"
+)
+
+func TestWaitGroup(t *testing.T) {
+	wg := NewWaitGroup()
+	_ = t
+	wg.Add(1)
+	ctx, cancel := context.WithTimeout(context.TODO(), 1*time.Second)
+	defer cancel()
+	wg.WaitContext(ctx)
+}