shithub: mc

ref: cf50193c7dc0c13d373d60982e7cb95168e0167e
dir: /lib/thread/sem.myr/

use std

use "atomic"

pkg thread =
	type sem = struct
		_val : uint32
	;;

	const mksem : (v : uint32 -> sem)
	const semwait : (s : sem# -> void)
	const semtrywait : (s : sem# -> bool)
	const sempost : (s : sem# -> void)
;;

const mksem = {v
	-> [._val = v]
}

const semwait = {s
	var v = 0

	for var i = 0; i < 1000; i++
		if (v = xget(&s._val)) != 0 && xcas(&s._val, v, v - 1) == v
			-> void
		;;
	;;

	for var i = 0; i < 1000; i++
		if (v = xget(&s._val)) != 0 && xcas(&s._val, v, v - 1) == v
			-> void
		;;
		std.nanosleep(10_000)
	;;

	for var i = 0; i < 1000; i++
		if (v = xget(&s._val)) != 0 && xcas(&s._val, v, v - 1) == v
			-> void
		;;
		std.nanosleep(100_000)
	;;

	for ; ;
		if (v = xget(&s._val)) != 0 && xcas(&s._val, v, v - 1) == v
			-> void
		;;
		std.nanosleep(1_000_000)
	;;
}

const semtrywait = {s
	for ; ;
		var v = xget(&s._val)
		if v == 0
			-> false
		;;
		if xcas(&s._val, v, v - 1) == v
			-> true
		;;
	;;
	-> false /* Unreachable */
}

const sempost = {s
	std.assert(xadd(&s._val, 1) != ~0x0, "error: semaphore overflowed\n")
}