SystemStreams

Used to check whether the system streams are all "original", i,e. they have not been overridden. Used for code paths that need to work differently if they have been overridden (e.g. handling subprocess stdout/stderr)

Assumes that the application only uses withStreams to override stdout/stderr/stdin.

The original non-override stderr, used for debugging purposes e.g. if you want to print stuff while the system streams override are messed up

Manages the global override of System.{in,out,err}. Overrides of those streams are global, so we cannot just override them per-use-site in a multithreaded environment because different threads may interleave and stomp over each other's over-writes. Instead, we over-write them globally with a set of streams that does nothing but forward to the per-thread ThreadLocalStreams.current streams, allowing callers to each reach their own thread-local streams without clashing across multiple threads

The original system streams of this process, before any redirection.

NOTE: you should not use this! They do not get captured properly by Mill's stdout/err redirection, and thus only get picked up from the Mill server log files asynchronously. That means that the logs may appear out of order, jumbling your logs and screwing up your terminal