use stduse "mutex"use "condvar" pkg thread =	type queue(@a) = struct		hd	: qnode(@a)#		tl	: qnode(@a)#		mtx	: mutex		cv	: cond	;; 	type qnode(@a) = struct		v	: @a		next	: qnode(@a)#	;; 	generic qinit	: (q : queue(@a)# -> void)	generic qget	: (q : queue(@a)# -> @a)	generic qput	: (q : queue(@a)#, v : @a -> void);; generic Znode = (0 : qnode(@a)#) generic qinit = {q	q.hd = Znode	q.tl = Znode	q.mtx = mkmtx()	q.cv = mkcond(&q.mtx)}  generic qput = {q, v : @a	var n : qnode(@a)# 	n = std.mk([.next=Znode, .v=v])	mtxlock(&q.mtx)	if q.hd == Znode		q.hd = n		q.tl = n	else		q.tl.next = n		q.tl = n	;;	condsignal(&q.cv)	mtxunlock(&q.mtx)} generic qget = {q	var n, v 	mtxlock(&q.mtx):again	if q.hd == Znode		condwait(&q.cv)		goto again	else		n = q.hd		q.hd = q.hd.next	;;	mtxunlock(&q.mtx)	v = n.v	std.free(n)	-> v}