shithub: mc

ref: d8bd5599e0e4b7919e3987ad80cb39f4a8aff63d
dir: /lib/thread/future+linux.myr/

use std
use sys

use "atomic.use"
use "common.use"

pkg thread =
	type future(@a) = struct
		_state	: int32
		_val	: @a
	;;

	generic mkfut	: (-> future(@a))
	generic futset	: (fut : future(@a)#, val : @a -> bool)
	generic futget	: (fut : future(@a)# -> @a)
	generic futtryget	: (fut : future(@a)# -> std.option(@a))
;;

const Clear = 0
const Setting = 1
const Set = 2

generic mkfut = {
	-> [._state = Clear ]
}

generic futset = {fut, val
	/* If we don't get a clear, we failed to set the value */
	if xcas(&fut._state, Clear, Setting) != Clear
		-> false
	;;
	fut._val = val
	fut._state = Set
	sys.futex(&fut._state, sys.Futexwake | sys.Futexpriv, 0x7fffffff, Zptr, Zptr, 0)
	-> true
}

generic futget = {fut
	var st

	/* we can transition from Set to Setting. */
	st = fut._state
	while st != Set
		sys.futex(&fut._state, sys.Futexwait | sys.Futexpriv, st, Zptr, Zptr, 0)
		st = fut._state
	;;
	-> fut._val
}