module Runtime_blockout_detector:sig..end
Runtime_blockout_detector is used detect bugs in C libraries that fail
    to release the OCaml runtime lock before making blocking calls.val start : ?callback:(elapsed:Core.Std.Time.Span.t -> unit) -> unit -> unitstart starts a thread that watches for blockouts where the OCaml
    lock isn't released.  By default, it prints a message to stderr.