shithub: mc

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Remove spin on unlock.

    It doesn't seem to help, so let's just drop it.

--- a/lib/thread/mutex+linux.myr

+++ b/lib/thread/mutex+linux.myr

@@ -12,13 +12,14 @@

 	const mtxlock	: (mtx : mutex# -> void)

 	const mtxtrylock	: (mtx : mutex# -> bool)

 	const mtxunlock	: (mtx : mutex# -> void)

+

+	pkglocal const Unlocked = 0

+	pkglocal const Locked = 1

+	pkglocal const Contended = 2

 ;;

-const Unlocked = 0

-const Locked = 1

-const Contended = 2

 generic Zptr = 0 castto(@a#)

-var nspin = 1	/* FIXME: pick a sane number, based on CPU count */

+var nspin = 10	/* FIXME: pick a sane number, based on CPU count */

 const mkmtx = {

 	-> [._state = Unlocked]

@@ -35,7 +36,6 @@

 		if c == Unlocked

 			->

 		;;

-		relax()

 	;;

 	/*

@@ -69,29 +69,6 @@

 		->

 	;;

-	/*

-	Contended case: Now we unlock, and wait a little bit to see if anyone

-	takes the lock. If someone takes the lock, we can avoid waking entering

-	the kernel to wake processes. However, we need to set the lock to contended

-	so that if there are still waiters, the thread that took the lock takes

-	responsibility for unlocking.

-	*/

-	for var i = 0; i < nspin; i++

-		if mtx._state != Unlocked

-			/*

-			If we're locked, set the state to contended to avoid

-			missed wakes.

-			*/

-			if xcas(&mtx._state, Locked, Contended) == Contended

-				->

-			;;

-		;;

-		relax()

-	;;

-

 	sys.futex(&mtx._state, sys.Futexwake | sys.Futexpriv, 1, Zptr, Zptr, 0)

 }

-const relax = {

-	/* FIXME: what is an appropriate way to kill CPU time without entering kernel? */

-}