shithub: mc

ref: beab0276a94c684f938ae5ea3d2c29c3dc331386
dir: /lib/thread/mutex+plan9.myr/

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use std
use sys


use "atomic"
use "common"

pkg thread =
	type mutex = struct
		_state	: int32
		_sem	: int32
	;;	

	const mkmtx	: (-> mutex)
	const mtxlock	: (mtx : mutex# -> void)
	const mtxtrylock	: (mtx : mutex# -> bool)
	const mtxunlock	: (mtx : mutex# -> void)
;;

const mkmtx = {
	-> [._state = 0, ._sem=0]
}

const mtxlock = {mtx
	/* if the old value was 0, we aren't contended */
	if xadd(&mtx._state, 1) == 0
		-> void
	;;
	
	while sys.semacquire(&mtx._sem, 1) < 0
		/* interrupted; retry */
	;;
}

const mtxtrylock = {mtx
	-> xcas(&mtx._state, 0, 1) == 0
}

	
const mtxunlock = {mtx
	/* if we were the only thread waiting on the lock, there was no contention */
	if xadd(&mtx._state, -1) == 1
		-> void
	;;

	sys.semrelease(&mtx._sem, 1)
}