# Join this thread to the calling thread
	#
	# Blocks until the method `main` returns or the target thread calls
	# `Sys::thread_exit`. Returns the object returned from the other thread.
	#
	# Stats the thread if now already done by a call to `start`.
	fun join: E
	do
		if native == null then start
		var r = native.join
		native = null
		return r.as(E)
	end