revid: using mutex to synchronise usage of Start and Stop

revid/revid.go

@@ -101,8 +101,11 @@ type Revid struct {
 	// encoders will hold the multiWriteCloser that writes to encoders from the lexer.
 	encoders io.WriteCloser
 
-	// isRunning is used to keep track of revid's running state between methods.
-	isRunning bool
+	// running is used to keep track of revid's running state between methods.
+	running bool
+
+	// mu is used to protect isRunning during concurrent use.
+	mu sync.Mutex
 
 	// wg will be used to wait for any processing routines to finish.
 	wg sync.WaitGroup
@@ -321,14 +324,17 @@ func (r *Revid) setupPipeline(mtsEnc func(dst io.WriteCloser, rate float64) (io.
 // Start invokes a Revid to start processing video from a defined input
 // and packetising (if theres packetization) to a defined output.
 //
-// Start is not safe for concurrent use.
+// Start is safe for concurrent use.
 func (r *Revid) Start() error {
-	if r.isRunning {
+	if r.IsRunning() {
 		r.config.Logger.Log(logger.Warning, pkg+"start called, but revid already running")
 		return nil
 	}
+
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
 	r.config.Logger.Log(logger.Info, pkg+"starting Revid")
-	r.isRunning = true
 	err := r.reset(r.config)
 	if err != nil {
 		r.Stop()
@@ -339,19 +345,23 @@ func (r *Revid) Start() error {
 		r.Stop()
 		return err
 	}
+	r.running = true
 	return nil
 }
 
 // Stop closes down the pipeline. This closes encoders and sender output routines,
 // connections, and/or files.
 //
-// Stop is not safe for concurrent use.
+// Stop is safe for concurrent use.
 func (r *Revid) Stop() {
-	if !r.isRunning {
+	if !r.IsRunning() {
 		r.config.Logger.Log(logger.Warning, pkg+"stop called but revid isn't running")
 		return
 	}
 
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
 	if r.closeInput != nil {
 		err := r.closeInput()
 		if err != nil {
@@ -370,18 +380,26 @@ func (r *Revid) Stop() {
 		r.cmd.Process.Kill()
 	}
 	r.wg.Wait()
-	r.isRunning = false
+	r.running = false
+}
+
+func (r *Revid) IsRunning() bool {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	return r.running
 }
 
 // Update takes a map of variables and their values and edits the current config
 // if the variables are recognised as valid parameters.
 //
-// Update is not safe for concurrent use.
+// Update is safe for concurrent use.
 func (r *Revid) Update(vars map[string]string) error {
-	if r.isRunning {
+	if r.IsRunning() {
 		r.Stop()
 	}
 
+	r.mu.Lock()
+	defer r.mu.Unlock()
 	//look through the vars and update revid where needed
 	for key, value := range vars {
 		switch key {