Swift's print is block-buffered when stdout is not connected to a TTY. Consumer
binaries will connect and receive messages correctly but produce no visible output.
To work around this, set NSUnbufferedIO=YES before running
any compiled tutorial binary, like so:
NSUnbufferedIO=YES .build/debug/Receive &
NSUnbufferedIO=YES .build/debug/Worker &
NSUnbufferedIO=YES .build/debug/RPCServer &This applies to all binaries, including producers, though producers are less affected since they exit promptly after sending.