Merge pull request 'sync/waitgroup: backport from master' (#320) from waitgroup into v3

Reviewed-on: #320

sync/waitgroup.go

@@ -0,0 +1,69 @@
+package sync
+
+import (
+	"context"
+	"sync"
+)
+
+type WaitGroup struct {
+	wg *sync.WaitGroup
+	c  int
+	mu sync.Mutex
+}
+
+func WrapWaitGroup(wg *sync.WaitGroup) *WaitGroup {
+	g := &WaitGroup{
+		wg: wg,
+	}
+	return g
+}
+
+func NewWaitGroup() *WaitGroup {
+	var wg sync.WaitGroup
+	return WrapWaitGroup(&wg)
+}
+
+func (g *WaitGroup) Add(n int) {
+	g.mu.Lock()
+	g.c += n
+	g.wg.Add(n)
+	g.mu.Unlock()
+}
+
+func (g *WaitGroup) Done() {
+	g.mu.Lock()
+	g.c += -1
+	g.wg.Add(-1)
+	g.mu.Unlock()
+}
+
+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.mu.Lock()
+		g.wg.Add(-g.c)
+		<-done
+		g.wg.Add(g.c)
+		g.mu.Unlock()
+		return
+	case <-done:
+		return
+	}
+}
+
+func (g *WaitGroup) Waiters() int {
+	g.mu.Lock()
+	c := g.c
+	g.mu.Unlock()
+	return c
+}

sync/waitgroup_test.go

@@ -0,0 +1,37 @@
+package sync
+
+import (
+	"context"
+	"testing"
+	"time"
+)
+
+func TestWaitGroupContext(t *testing.T) {
+	wg := NewWaitGroup()
+	_ = t
+	wg.Add(1)
+	ctx, cancel := context.WithTimeout(context.TODO(), 1*time.Second)
+	defer cancel()
+	wg.WaitContext(ctx)
+}
+
+func TestWaitGroupReuse(t *testing.T) {
+	wg := NewWaitGroup()
+	defer func() {
+		if wg.Waiters() != 0 {
+			t.Fatal("lost goroutines")
+		}
+	}()
+
+	wg.Add(1)
+	defer wg.Done()
+	ctx, cancel := context.WithTimeout(context.TODO(), 1*time.Second)
+	defer cancel()
+	wg.WaitContext(ctx)
+
+	wg.Add(1)
+	defer wg.Done()
+	ctx, cancel = context.WithTimeout(context.TODO(), 1*time.Second)
+	defer cancel()
+	wg.WaitContext(ctx)
+}