Fix race in reload action

Fix #4070

Author: junegunn

src/core.go

@@ -299,7 +299,7 @@ func Run(opts *Options) (int, error) {
 		itemIndex = 0
 		inputRevision.bumpMajor()
 		header = make([]string, 0, opts.HeaderLines)
-		go reader.restart(command, environ)
+		reader.restart(command, environ)
 	}
 
 	exitCode := ExitOk

src/reader.go

@@ -25,16 +25,24 @@ type Reader struct {
 	event    int32
 	finChan  chan bool
 	mutex    sync.Mutex
-	exec     *exec.Cmd
-	execOut  io.ReadCloser
+	termFunc func()
 	command  *string
-	killed   bool
 	wait     bool
 }
 
 // NewReader returns new Reader object
 func NewReader(pusher func([]byte) bool, eventBox *util.EventBox, executor *util.Executor, delimNil bool, wait bool) *Reader {
-	return &Reader{pusher, executor, eventBox, delimNil, int32(EvtReady), make(chan bool, 1), sync.Mutex{}, nil, nil, nil, false, wait}
+	return &Reader{
+		pusher,
+		executor,
+		eventBox,
+		delimNil,
+		int32(EvtReady),
+		make(chan bool, 1),
+		sync.Mutex{},
+		func() { os.Stdin.Close() },
+		nil,
+		wait}
 }
 
 func (r *Reader) startEventPoller() {
@@ -61,6 +69,10 @@ func (r *Reader) startEventPoller() {
 	}()
 }
 
+func (r *Reader) wasKilled() bool {
+	return r.termFunc == nil
+}
+
 func (r *Reader) fin(success bool) {
 	atomic.StoreInt32(&r.event, int32(EvtReadFin))
 	if r.wait {
@@ -69,7 +81,7 @@ func (r *Reader) fin(success bool) {
 
 	r.mutex.Lock()
 	ret := r.command
-	if success || r.killed {
+	if success || r.wasKilled() {
 		ret = nil
 	}
 	r.mutex.Unlock()
@@ -79,22 +91,27 @@ func (r *Reader) fin(success bool) {
 
 func (r *Reader) terminate() {
 	r.mutex.Lock()
-	r.killed = true
-	if r.exec != nil && r.exec.Process != nil {
-		r.execOut.Close()
-		util.KillCommand(r.exec)
-	} else {
-		os.Stdin.Close()
+	if r.termFunc != nil {
+		r.termFunc()
+		r.termFunc = nil
 	}
 	r.mutex.Unlock()
 }
 
 func (r *Reader) restart(command commandSpec, environ []string) {
 	r.event = int32(EvtReady)
 	r.startEventPoller()
-	success := r.readFromCommand(command.command, environ)
-	r.fin(success)
-	removeFiles(command.tempFiles)
+
+	r.mutex.Lock()
+	defer r.mutex.Unlock()
+
+	if exec, execOut := r.startCommand(command.command, environ); exec != nil {
+		go func() {
+			success := r.feedCommandOutput(exec, execOut)
+			r.fin(success)
+			removeFiles(command.tempFiles)
+		}()
+	}
 }
 
 func (r *Reader) readChannel(inputChan chan string) bool {
@@ -249,7 +266,6 @@ func trimPath(path string) string {
 }
 
 func (r *Reader) readFiles(root string, opts walkerOpts, ignores []string) bool {
-	r.killed = false
 	conf := fastwalk.Config{
 		Follow: opts.follow,
 		// Use forward slashes when running a Windows binary under WSL or MSYS
@@ -280,39 +296,47 @@ func (r *Reader) readFiles(root string, opts walkerOpts, ignores []string) bool
 		}
 		r.mutex.Lock()
 		defer r.mutex.Unlock()
-		if r.killed {
+		if r.wasKilled() {
 			return context.Canceled
 		}
 		return nil
 	}
 	return fastwalk.Walk(&conf, root, fn) == nil
 }
 
-func (r *Reader) readFromCommand(command string, environ []string) bool {
-	r.mutex.Lock()
-	r.killed = false
+// Should be called with the mutex held
+func (r *Reader) startCommand(command string, environ []string) (*exec.Cmd, io.ReadCloser) {
+	r.termFunc = nil
 	r.command = &command
-	r.exec = r.executor.ExecCommand(command, true)
+	exec := r.executor.ExecCommand(command, true)
 	if environ != nil {
-		r.exec.Env = environ
+		exec.Env = environ
 	}
-
-	var err error
-	r.execOut, err = r.exec.StdoutPipe()
-	if err != nil {
-		r.exec = nil
-		r.mutex.Unlock()
-		return false
+	execOut, err := exec.StdoutPipe()
+	if err != nil || exec.Start() != nil {
+		return nil, nil
 	}
 
-	err = r.exec.Start()
-	if err != nil {
-		r.exec = nil
-		r.mutex.Unlock()
-		return false
+	// Function to call to terminate the running command
+	r.termFunc = func() {
+		execOut.Close()
+		util.KillCommand(exec)
 	}
 
+	return exec, execOut
+}
+
+func (r *Reader) feedCommandOutput(exec *exec.Cmd, execOut io.ReadCloser) bool {
+	r.feed(execOut)
+	return exec.Wait() == nil
+}
+
+func (r *Reader) readFromCommand(command string, environ []string) bool {
+	r.mutex.Lock()
+	exec, execOut := r.startCommand(command, environ)
 	r.mutex.Unlock()
-	r.feed(r.execOut)
-	return r.exec.Wait() == nil
+	if exec == nil {
+		return false
+	}
+	return r.feedCommandOutput(exec, execOut)
 }