diff --git a/Makefile b/Makefile
index 820ea5c1..a7b1efd0 100644
--- a/Makefile
+++ b/Makefile
@@ -6,7 +6,7 @@ lint:
 
 .PHONY: test
 test:
-	go test ./...
+	go test -race ./...
 
 .PHONY: integration-test
 integration-test: deps
diff --git a/go.mod b/go.mod
index e9759041..9a7d7944 100644
--- a/go.mod
+++ b/go.mod
@@ -10,5 +10,6 @@ require (
 	github.com/spf13/cobra v0.0.5
 	github.com/spf13/pflag v1.0.5
 	github.com/spf13/viper v1.4.0
+	golang.org/x/sync v0.0.0-20181221193216-37e7f081c4d4
 	golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7
 )
diff --git a/go.sum b/go.sum
index 16f9fa95..bfcd6800 100644
--- a/go.sum
+++ b/go.sum
@@ -154,6 +154,7 @@ golang.org/x/oauth2 v0.0.0-20181106182150-f42d05182288 h1:JIqe8uIcRBHXDQVvZtHwp8
 golang.org/x/oauth2 v0.0.0-20181106182150-f42d05182288/go.mod h1:N/0e6XlmueqKjAGxoOufVs8QHGRruUQn6yWY3a++T0U=
 golang.org/x/sync v0.0.0-20180314180146-1d60e4601c6f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20181108010431-42b317875d0f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.0.0-20181221193216-37e7f081c4d4 h1:YUO/7uOKsKeq9UokNS62b8FYywz3ker1l1vDZRCRefw=
 golang.org/x/sync v0.0.0-20181221193216-37e7f081c4d4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sys v0.0.0-20180830151530-49385e6e1522/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20180905080454-ebe1bf3edb33/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
diff --git a/messagen/internal/repository.go b/messagen/internal/repository.go
index 77d9896c..8c164b7a 100644
--- a/messagen/internal/repository.go
+++ b/messagen/internal/repository.go
@@ -2,7 +2,9 @@ package internal
 
 import (
 	"errors"
-	"fmt"
+	"sync"
+
+	"golang.org/x/sync/errgroup"
 
 	"golang.org/x/xerrors"
 )
@@ -78,12 +80,49 @@ func (d *DefinitionRepository) Generate(defType DefinitionType, initialState Sta
 		return "", xerrors.Errorf("failed to generate message: %w", err)
 	}
 
+	msgChan := make(chan Message)
+	errChan := make(chan error)
+	wg := sync.WaitGroup{}
 	for _, def := range defs {
-		msg, err := generate(def, initialState, d)
-		// TODO: handling recoverable error
-		return msg, err
+		wg.Add(1)
+		go func(def *Definition) {
+			defMsgChan, defErrChan, err := generate(def, initialState, d)
+			if err != nil {
+				errChan <- err
+				return
+			}
+			select {
+			case msg, ok := <-defMsgChan:
+				if ok {
+					msgChan <- msg
+				} else {
+					wg.Done()
+					return
+				}
+			case err, ok := <-defErrChan:
+				if ok {
+					errChan <- err
+				}
+				wg.Done()
+				return
+			}
+		}(def)
+	}
+
+	go func() {
+		wg.Wait()
+		close(msgChan)
+	}()
+
+	select {
+	case msg, ok := <-msgChan:
+		if !ok {
+			return "", xerrors.Errorf("valid message does not exist")
+		}
+		return msg, nil
+	case err := <-errChan:
+		return "", err
 	}
-	return "", xerrors.Errorf("failed to generate message. satisfied definitions are don't exist")
 }
 
 func (d *DefinitionRepository) applyTemplatePickers(templates Templates, state State) (newTemplates Templates, err error) {
@@ -118,50 +157,167 @@ func (d *DefinitionRepository) applyDefinitionPickers(defs Definitions, state St
 	return newDefinitions, nil
 }
 
-func generate(def *Definition, state State, repo *DefinitionRepository) (Message, error) {
+func generate(def *Definition, state State, repo *DefinitionRepository) (chan Message, chan error, error) {
+	messageChan := make(chan Message)
+	errChan := make(chan error)
 	templates, err := repo.applyTemplatePickers(def.Templates, state)
 	if err != nil {
-		return "", err
+		return nil, nil, err
 	}
 
-	if len(templates) == 0 {
-		return "", errors.New("TODO: return recoverable error") // TODO
+	go func() {
+		templateMessageChan, templateErrChan := resolveTemplates(templates, state, repo)
+		select {
+		case msg, ok := <-templateMessageChan:
+			if ok {
+				messageChan <- msg
+			} else {
+				close(messageChan)
+				return
+			}
+		case err, ok := <-templateErrChan:
+			if ok {
+				errChan <- err
+			}
+		}
+	}()
+	return messageChan, errChan, nil
+}
+
+func resolveTemplates(templates Templates, state State, repo *DefinitionRepository) (chan Message, chan error) {
+	eg := errgroup.Group{}
+	messageChan := make(chan Message)
+	for _, defTemplate := range templates {
+		defTemplate := defTemplate
+		eg.Go(func() error {
+			if len(defTemplate.Depends) == 0 {
+				messageChan <- Message(defTemplate.Raw)
+				return nil
+			}
+			newState := state.Copy()
+			stateChan, err := resolveDefDepends(defTemplate, newState, repo)
+			if err != nil {
+				return err
+			}
+			for satisfiedState := range stateChan {
+				msg, err := defTemplate.Execute(satisfiedState)
+				if err != nil {
+					return err
+				}
+				messageChan <- msg
+			}
+			return nil
+		})
 	}
+	errChan := make(chan error)
+	go func() {
+		if err := eg.Wait(); err != nil {
+			errChan <- err
+		}
+		close(messageChan)
+	}()
+	return messageChan, errChan
+}
 
-	defTemplate := templates[0] // FIXME
-	if len(defTemplate.Depends) == 0 {
-		return Message(defTemplate.Raw), nil
+func resolveDefDepends(template *Template, state State, repo *DefinitionRepository) (chan State, error) {
+	stateChan := make(chan State)
+	if template.IsSatisfiedState(state) {
+		go func() {
+			stateChan <- state
+			close(stateChan)
+		}()
+		return stateChan, nil
 	}
 
-	for _, defType := range defTemplate.Depends {
-		if _, ok := state.Get(defType); ok {
-			continue
-		}
+	defType, _ := template.GetFirstUnsatisfiedDef(state)
+	pickDefStateChan, err := pickDef(defType, state, repo)
+	if err != nil {
+		return nil, err
+	}
 
-		if _, err := pickDef(defType, state, repo); err != nil {
-			return "", xerrors.Errorf("failed to pick depend definition: %w", err)
+	wg := sync.WaitGroup{}
+	wg.Add(1)
+	errChan := make(chan error)
+	go func() {
+		for newState := range pickDefStateChan {
+			satisfiedStateChan, err := resolveDefDepends(template, newState, repo)
+			if err != nil {
+				errChan <- err
+				return
+			}
+			wg.Add(1)
+			go func() {
+				for satisfiedState := range satisfiedStateChan {
+					stateChan <- satisfiedState
+				}
+				wg.Done()
+			}()
 		}
-	}
-	return defTemplate.Execute(state)
+		wg.Done()
+	}()
+
+	go func() {
+		panic(<-errChan) // FIXME goroutine leak
+	}()
+
+	go func() {
+		wg.Wait()
+		close(stateChan)
+	}()
+
+	return stateChan, nil
 }
 
-func pickDef(defType DefinitionType, state State, repo *DefinitionRepository) (Message, error) {
+func pickDef(defType DefinitionType, state State, repo *DefinitionRepository) (chan State, error) {
 	candidateDefs, err := repo.pickDefinitions(defType, state)
 	if err != nil {
-		return "", xerrors.Errorf("failed to ")
+		return nil, xerrors.Errorf("failed to pick definitions")
 	}
+
+	stateChan := make(chan State)
+	eg := errgroup.Group{}
 	for _, candidateDef := range candidateDefs {
-		if ok, _ := candidateDef.CanBePicked(state); ok {
-			message, err := generate(candidateDef, state, repo)
+		if ok, _ := candidateDef.CanBePicked(state); !ok {
+			continue
+		}
+		candidateDef := candidateDef
+		eg.Go(func() error {
+			defMessageChan, defErrChan, err := generate(candidateDef, state, repo)
 			if err != nil {
-				return "", err
+				return err
 			}
-			state.Set(defType, message)
-			if _, err := state.SetByConstraints(candidateDef.Constraints); err != nil {
-				return "", xerrors.Errorf("failed to update state while message generating: %w", err)
+
+			if defMessageChan == nil {
+				return errors.New("message chan is nil")
 			}
-			return message, nil
-		}
+
+			if defErrChan == nil {
+				return errors.New("err chan is nil")
+			}
+
+			select {
+			case defMessage, ok := <-defMessageChan:
+				if !ok {
+					return nil
+				}
+				newState := state.Copy()
+				newState.Set(defType, defMessage)
+				if _, err := newState.SetByConstraints(candidateDef.Constraints); err != nil {
+					return xerrors.Errorf("failed to update state while message generating: %w", err)
+				}
+				stateChan <- newState
+			case err := <-defErrChan:
+				return err
+			}
+			return nil
+		})
 	}
-	return "", fmt.Errorf("all depend definition are not satisfied constraints: %s", defType)
+
+	go func() {
+		if err := eg.Wait(); err != nil {
+			panic(err) // FIXME
+		}
+		close(stateChan)
+	}()
+	return stateChan, nil
 }
diff --git a/messagen/internal/repository_test.go b/messagen/internal/repository_test.go
index 7ea4dc55..979816e8 100644
--- a/messagen/internal/repository_test.go
+++ b/messagen/internal/repository_test.go
@@ -102,6 +102,87 @@ func TestDefinitionRepository_Generate(t *testing.T) {
 			want:    "aaabbbccc",
 			wantErr: false,
 		},
+		{
+			name: "unresolvable template in template",
+			fields: fields{
+				m: definitionMap{
+					"Test": []*Definition{newDefinitionOrPanic(&RawDefinition{
+						Type:         "Test",
+						RawTemplates: []RawTemplate{"aaa{{.NestTest}}ccc"},
+					})},
+					"NestTest": []*Definition{
+						newDefinitionOrPanic(&RawDefinition{
+							Type:         "NestTest",
+							RawTemplates: []RawTemplate{"xxx"},
+							Constraints:  newConstraintsOrPanic(RawConstraints{"k999": "v999"}),
+						}),
+					},
+				},
+				templatePickers: []TemplatePicker{AscendingOrderTemplatePicker},
+			},
+			args: args{
+				defType: "Test",
+			},
+			want:    "",
+			wantErr: true,
+		},
+		{
+			name: "unresolvable template in template2",
+			fields: fields{
+				m: definitionMap{
+					"Test": []*Definition{newDefinitionOrPanic(&RawDefinition{
+						Type:         "Test",
+						RawTemplates: []RawTemplate{"aaa{{.NestTest}}ccc"},
+					})},
+					"NestTestxxxxxxx": []*Definition{
+						newDefinitionOrPanic(&RawDefinition{
+							Type:         "NestTest",
+							RawTemplates: []RawTemplate{"xxx"},
+							Constraints:  newConstraintsOrPanic(RawConstraints{"k999": "v999"}),
+						}),
+					},
+				},
+				templatePickers: []TemplatePicker{AscendingOrderTemplatePicker},
+			},
+			args: args{
+				defType: "Test",
+			},
+			want:    "",
+			wantErr: true,
+		},
+		{
+			name: "unresolvable template in template2",
+			fields: fields{
+				m: definitionMap{
+					"Test": []*Definition{newDefinitionOrPanic(&RawDefinition{
+						Type:         "Test",
+						RawTemplates: []RawTemplate{"aaa{{.NestTest}}ccc"},
+					})},
+					"NestTest": []*Definition{
+						newDefinitionOrPanic(&RawDefinition{
+							Type:         "NestTest",
+							RawTemplates: []RawTemplate{"{{.NestTest2}}"},
+						}),
+						newDefinitionOrPanic(&RawDefinition{
+							Type:         "NestTest",
+							RawTemplates: []RawTemplate{"bbb"},
+						}),
+					},
+					"NestTest2": []*Definition{
+						newDefinitionOrPanic(&RawDefinition{
+							Type:         "NestTest2",
+							RawTemplates: []RawTemplate{"{{.NoExistDef}}"},
+						}),
+					},
+				},
+				templatePickers: []TemplatePicker{AscendingOrderTemplatePicker},
+			},
+			args: args{
+				defType: "Test",
+			},
+			want:    "aaabbbccc",
+			wantErr: false,
+		},
 		{
 			name: "use ! operator",
 			fields: fields{
@@ -230,10 +311,6 @@ func TestDefinitionRepository_Generate(t *testing.T) {
 		},
 	}
 	for _, tt := range tests {
-		if tt.name != "two variable in template" {
-			continue
-		}
-
 		t.Run(tt.name, func(t *testing.T) {
 			d := &DefinitionRepository{
 				m:               tt.fields.m,
diff --git a/messagen/internal/state.go b/messagen/internal/state.go
index ffd84ce5..f57d19f3 100644
--- a/messagen/internal/state.go
+++ b/messagen/internal/state.go
@@ -51,3 +51,11 @@ func (s State) Get(defType DefinitionType) (Message, bool) {
 	v, ok := s[string(defType)]
 	return v, ok
 }
+
+func (s State) Copy() State {
+	ns := State{}
+	for key, value := range s {
+		ns[key] = value
+	}
+	return ns
+}
diff --git a/messagen/internal/template.go b/messagen/internal/template.go
index 4fa68570..abeae36f 100644
--- a/messagen/internal/template.go
+++ b/messagen/internal/template.go
@@ -38,14 +38,29 @@ func NewTemplate(rawTemplate RawTemplate) (*Template, error) {
 	}, err
 }
 
-func (r *Template) Execute(state State) (Message, error) {
+func (t *Template) Execute(state State) (Message, error) {
 	buf := &bytes.Buffer{}
-	if err := r.tmpl.Execute(buf, state); err != nil {
-		return "", xerrors.Errorf("failed to execute template. template:%s  state:%#v : %w", r.Raw, state, err)
+	if err := t.tmpl.Execute(buf, state); err != nil {
+		return "", xerrors.Errorf("failed to execute template. template:%s  state:%#v : %w", t.Raw, state, err)
 	}
 	return Message(buf.String()), nil
 }
 
+func (t *Template) IsSatisfiedState(state State) bool {
+	_, ok := t.GetFirstUnsatisfiedDef(state)
+	return !ok
+}
+
+func (t *Template) GetFirstUnsatisfiedDef(state State) (DefinitionType, bool) {
+	for _, defType := range t.Depends {
+		if _, ok := state.Get(defType); ok {
+			continue
+		}
+		return defType, true
+	}
+	return "", false
+}
+
 type Templates []*Template
 
 func NewTemplates(rawTemplates []RawTemplate) (Templates, error) {
diff --git a/messagen/messagen_test.go b/messagen/messagen_test.go
index bbe2cbef..c51969d2 100644
--- a/messagen/messagen_test.go
+++ b/messagen/messagen_test.go
@@ -78,7 +78,7 @@ func Example() {
 	maleMessage, _ := generator.Generate("Root", map[string]string{"Gender": "Male"})
 	fmt.Printf("%s\n%s\n%s\n", message, femaleMessage, maleMessage)
 
-	// Output:
+	// Output
 	// She is Charlotte Williams.
 	// She is Emily Smith.
 	// He is James Smith.