shithub: mc

ref: 4fd18f1c27d3f1eba10c849a3c9cdb7d9dc33abc
dir: /lib/thread/condvar+freebsd.myr/

use std
use sys

use "atomic"
use "common"
use "mutex"

pkg thread =
	type cond = struct
		_mtx	: mutex#
		_seq	: uint32
	;;

	const mkcond	: (mtx : mutex# -> cond)
	const condwait	: (cond : cond# -> void)
	const condsignal	: (cond : cond# -> void)
	const condbroadcast	: (cond : cond# -> void)
;;

const mkcond = {mtx
	-> [._mtx = mtx, ._seq = 0]
}

const condwait = {cond
	var seq
	var mtx

	mtx = cond._mtx
	seq = cond._seq

	mtxunlock(mtx)
	sys.umtx_op((&cond._seq : void#), \
		sys.Umtxwaituintpriv, \
		(seq : uint64), \
		Zptr, Zptr)

	/*
	We need to atomically set the mutex to contended. This allows us to
	pass responsibility for waking up the potential other waiters on to the
	unlocker of the mutex.
	*/
	while xchg(&mtx._state, Contended) != Unlocked
		sys.umtx_op((&mtx._state : void#), \
			sys.Umtxwaituintpriv, \
			(Contended : uint64), \
			Zptr, Zptr)
	;;
}

const condsignal = {cond : cond#
	xadd(&cond._seq, 1)
	sys.umtx_op((&cond._seq : void#), sys.Umtxwakepriv, 1, Zptr, Zptr)
}

const condbroadcast = {cond : cond#
	xadd(&cond._seq, 1)
	sys.umtx_op((&cond._seq : void#), sys.Umtxwakepriv, 0x7ffffff, Zptr, Zptr)
}