Fix data race in prompt and select

ref: manifoldco#185

prompt.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"io"
 	"strings"
+	"sync"
 	"text/template"
 
 	"github.com/chzyer/readline"
@@ -157,8 +158,11 @@ func (p *Prompt) Run() (string, error) {
 	}
 	eraseDefault := input != "" && !p.AllowEdit
 	cur := NewCursor(input, p.Pointer, eraseDefault)
+	var curLock sync.Mutex
 
 	listen := func(input []rune, pos int, key rune) ([]rune, int, bool) {
+		defer curLock.Unlock()
+		curLock.Lock()
 		_, _, keepOn := cur.Listen(input, pos, key)
 		err := validFn(cur.Get())
 		var prompt []byte
@@ -193,7 +197,10 @@ func (p *Prompt) Run() (string, error) {
 
 	for {
 		_, err = rl.Readline()
+		curLock.Lock()
 		inputErr = validFn(cur.Get())
+		curLock.Unlock()
+
 		if inputErr == nil {
 			break
 		}
@@ -203,6 +210,9 @@ func (p *Prompt) Run() (string, error) {
 		}
 	}
 
+	defer curLock.Unlock()
+	curLock.Lock()
+
 	if err != nil {
 		switch err {
 		case readline.ErrInterrupt:

select.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"sync"
 	"text/tabwriter"
 	"text/template"
 
@@ -246,6 +247,7 @@ func (s *Select) innerRun(cursorPos, scroll int, top rune) (int, string, error)
 	rl.Write([]byte(hideCursor))
 	sb := screenbuf.New(rl)
 
+	var curLock sync.Mutex
 	cur := NewCursor("", s.Pointer, false)
 
 	canSearch := s.Searcher != nil
@@ -254,6 +256,9 @@ func (s *Select) innerRun(cursorPos, scroll int, top rune) (int, string, error)
 	s.list.SetStart(scroll)
 
 	c.SetListener(func(line []rune, pos int, key rune) ([]rune, int, bool) {
+		defer curLock.Unlock()
+		curLock.Lock()
+
 		switch {
 		case key == KeyEnter:
 			return nil, 0, true
@@ -373,6 +378,9 @@ func (s *Select) innerRun(cursorPos, scroll int, top rune) (int, string, error)
 
 	}
 
+	defer curLock.Unlock()
+	curLock.Lock()
+
 	if err != nil {
 		if err.Error() == "Interrupt" {
 			err = ErrInterrupt