fix memory leak when creating streams that already exist (#3)

[jzbyers]

Bug Description

When creating a stream via CreateStream(), a new stream is always created even if a stream with the same id already exists, causing a memory leak where goroutines are created via str.run() but never closed.

How to Read This PR

This PR fixes that bug by closing the newly created stream if the stream id is found in the server's map of streams.

How to Test This PR

These changes are reflected in the tests, but there is a potential race condition where the newly created stream might not have been closed by the time the test checks whether runtime.NumGoroutine() is equal to numGoRoutines.

At the moment I can't think of a better, simple way to test this so if you'd prefer to not have an imperfect test in server_test.go, let me know and I will remove it. Thanks!

make test

[purehyperbole]

Thanks for the PR!

I think this can be avoided altogether, by reordering this function so that we create a stream after checking if it already exists. Something like:

func (s *Server) CreateStream(id string) *Stream {
	s.mu.Lock()
	defer s.mu.Unlock()

	if s.Streams[id] != nil {
		return s.Streams[id]
	}

	str := newStream(s.BufferSize, s.AutoReplay)
	str.run()

	s.Streams[id] = str

	return str
}

That should avoid the race condition you mentioned. What do you think?

[jzbyers]

Nice! That's simpler to understand. Changing now.