Goroutines and mutex

Question

func (s *Server) start() {
         s.Lock()
         defer s.Unlock()
        if !s.isClosed{
           go s.processing()
        }
        go s.start()
 }

func (s *Server) processing() {
  s.Lock()
  // do stuff
  s.Unlock()
}

I have a working Golang project that has a block of code following the logic shown above.

I don't understand why this logic works as I would've expected a deadlock.

Answer 1

We'll call the initial goroutine that's running when start is entered G1.

1. start (in G1) locks the mutex and defers the unlock until start returns.
2. start calls s.processing in a new goroutine (G2)
3. start calls itself in a new goroutine (G3)
4. start (G1) unlocks the mutex and returns.

None of those calls except the lock at Step 1 is a blocking call. Concurrently, in G2, s.processing waits for start to unlock the mutex (which will happen pretty quickly because all start does is start a couple goroutines before unlocking the mutex). Also concurrently, in G3, the above 4 steps are performed all over again (on an apparently infinite loop).

There is no point in that logic that could cause a deadlock.