Added the ErrorGroup

errgroup.go

@@ -0,0 +1,73 @@
+package waitgroup
+
+import (
+	"context"
+	"sync"
+)
+
+// An ErrorGroup is a collection of goroutines working on subtasks that are part of
+// the same overall task.
+type ErrorGroup struct {
+	size int
+	pool chan byte
+
+	cancel func()
+
+	wg sync.WaitGroup
+
+	errOnce sync.Once
+	err     error
+}
+
+// NewErrorGroup returns a new ErrorGroup instance
+func NewErrorGroup(ctx context.Context, size int) (*ErrorGroup, context.Context) {
+	ctx, cancel := context.WithCancel(ctx)
+	wg := &ErrorGroup{
+		size:   size,
+		cancel: cancel,
+	}
+	if size > 0 {
+		wg.pool = make(chan byte, size)
+	}
+	return wg, ctx
+}
+
+// Wait blocks until all function calls from the Go method have returned, then
+// returns the first non-nil error (if any) from them.
+func (g *ErrorGroup) Wait() error {
+	g.wg.Wait()
+	if g.cancel != nil {
+		g.cancel()
+	}
+	return g.err
+}
+
+// Add calls the given function in a new goroutine.
+//
+// The first call to return a non-nil error cancels the group; its error will be
+// returned by Wait.
+func (g *ErrorGroup) Add(f func() error) {
+
+	if g.size > 0 {
+		g.pool <- 1
+	}
+	g.wg.Add(1)
+
+	go func() {
+		defer func() {
+			if g.size > 0 {
+				<-g.pool
+			}
+			g.wg.Done()
+		}()
+
+		if err := f(); err != nil {
+			g.errOnce.Do(func() {
+				g.err = err
+				if g.cancel != nil {
+					g.cancel()
+				}
+			})
+		}
+	}()
+}

errgroup_test.go

@@ -0,0 +1,46 @@
+package waitgroup_test
+
+import (
+	"context"
+	"testing"
+
+	"github.com/pkg/errors"
+	"github.com/stretchr/testify/assert"
+
+	"github.com/pieterclaerhout/go-waitgroup"
+)
+
+func Test_ErrorGroup_Add(t *testing.T) {
+
+	type test struct {
+		name string
+		size int
+	}
+
+	var tests = []test{
+		{"single", 1},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+
+			ctx := context.Background()
+
+			wg, _ := waitgroup.NewErrorGroup(ctx, tc.size)
+			assert.NotNil(t, wg)
+
+			wg.Add(func() error {
+				return nil
+			})
+
+			wg.Add(func() error {
+				return errors.New("An error occurred")
+			})
+
+			err := wg.Wait()
+			assert.Error(t, err)
+
+		})
+	}
+
+}

go.mod

@@ -2,4 +2,8 @@ module github.com/pieterclaerhout/go-waitgroup
 
 go 1.12
 
-require github.com/stretchr/testify v1.4.0
+require (
+	github.com/pkg/errors v0.8.1
+	github.com/stretchr/testify v1.4.0
+	golang.org/x/sync v0.0.0-20190911185100-cd5d95a43a6e
+)

go.sum

@@ -1,11 +1,15 @@
 github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pkg/errors v0.8.1 h1:iURUrRGxPUNPdy5/HRSm+Yj6okJ6UtLINN0Q9M4+h3I=
+github.com/pkg/errors v0.8.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/stretchr/objx v0.1.0 h1:4G4v2dO3VZwixGIRoQ5Lfboy6nUhCyYzaqnIAPPhYs4=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v1.4.0 h1:2E4SXV/wtOkTonXsotYi4li6zVWxYlZuYNCXe9XRJyk=
 github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
+golang.org/x/sync v0.0.0-20190911185100-cd5d95a43a6e h1:vcxGaoTs7kV8m5Np9uUNQin4BrLOthgV7252N8V+FwY=
+golang.org/x/sync v0.0.0-20190911185100-cd5d95a43a6e/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v2 v2.2.2 h1:ZCJp+EgiOT7lHqUV2J862kp8Qj64Jo6az82+3Td9dZw=
 gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=

waitgroup.go

@@ -2,7 +2,6 @@ package waitgroup
 
 import (
 	"sync"
-	// "sync/atomic"
 )
 
 // WaitGroup implements a simple goruntine pool.

waitgroup_test.go

@@ -8,7 +8,7 @@ import (
 	"github.com/pieterclaerhout/go-waitgroup"
 )
 
-func Test_Waitgroup(t *testing.T) {
+func Test_WaitGroup(t *testing.T) {
 
 	type test struct {
 		name string
@@ -24,6 +24,7 @@ func Test_Waitgroup(t *testing.T) {
 
 			wg := waitgroup.NewWaitGroup(tc.size)
 			assert.NotNil(t, wg)
+
 			assert.Zero(t, wg.PendingCount(), "pending-before")
 
 			wg.BlockAdd()
@@ -41,3 +42,29 @@ func Test_Waitgroup(t *testing.T) {
 	}
 
 }
+
+func Test_WaitGroup_Add(t *testing.T) {
+
+	type test struct {
+		name string
+		size int
+	}
+
+	var tests = []test{
+		{"single", 1},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+
+			wg := waitgroup.NewWaitGroup(tc.size)
+			assert.NotNil(t, wg)
+
+			wg.Add(func() {})
+
+			wg.Wait()
+
+		})
+	}
+
+}