Async.UnixBasic abstraction for a worker.
val outcome_t : outcome Irmin.Type.tval status_t : status Irmin.Type.tval async : (unit -> unit) -> tStart a task.
If running, wait for a task to finish and return its outcome.
If not running, return the oucome of the task.
If running, refresh the status of the task, without blocking.
If not running, return the oucome of the task.
val cancel : t -> boolIf running, cancel the task and return true.
If not running, do nothing and return false.