Stream: post first read events from client and upstream. The main proxy function ngx_stream_proxy_process() can terminate the stream session. The code, following it, should check its return code to make sure the session still exists. This happens in client and upstream initialization functions. Swapping ngx_stream_proxy_process() call with the code, that follows it, leaves the same problem vice versa. In future ngx_stream_proxy_process() will call ngx_stream_proxy_next_upstream() making it too complicated to know if stream session still exists after this call. Now ngx_stream_proxy_process() is called from posted event handlers in both places with no code following it. The posted event is automatically removed once session is terminated.