Initiates an orderly shutdown in which preexisting calls continue but new calls are rejected. After this call returns, this server has released the listening socket(s) and may be reused by another server.
Note that this method will not wait for preexisting calls to finish before returning. awaitTermination needs to be called to wait for existing calls to finish.
Calling this method before start will shut down and terminate the server like normal, but prevents starting the server in the future.
Return
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