reverting semaphore lock changes from sources (r41ccd6d221da, rb28756e5ba29)

semaphore locks have much higher overhead than initially presented
in the "Semaphores in Plan9" paper. until the reason for it has been
found out i will revert the changes.

1 files changed, 14 insertions, 23 deletions

diff --git a/sys/src/ape/lib/ap/arm/lock.c b/sys/src/ape/lib/ap/arm/lock.c
index 65a65df7b..91c0ba233 100644
--- a/sys/src/ape/lib/ap/arm/lock.c
+++ b/sys/src/ape/lib/ap/arm/lock.c
@@ -1,35 +1,26 @@
-#include "../plan9/lib.h"
-#include "../plan9/sys9.h"
 #define _LOCK_EXTENSION
+#include "../plan9/sys9.h"
 #include <lock.h>
 
+int	tas(int*);
+
 void
-lock(Lock *l)
+lock(Lock *lk)
 {
-	if(ainc(&l->key) == 1)
-		return;	/* changed from 0 -> 1: we hold lock */
-	/* otherwise wait in kernel */
-	while(_SEMACQUIRE(&l->sem, 1) < 0){
-		/* interrupted; try again */
-	}
+	while(tas(&lk->val))
+		_SLEEP(0);
 }
 
-void
-unlock(Lock *l)
+int
+canlock(Lock *lk)
 {
-	if(adec(&l->key) == 0)
-		return;	/* changed from 1 -> 0: no contention */
-	_SEMRELEASE(&l->sem, 1);
+	if(tas(&lk->val))
+		return 0;
+	return 1;
 }
 
-int
-canlock(Lock *l)
+void
+unlock(Lock *lk)
 {
-	if(ainc(&l->key) == 1)
-		return 1;	/* changed from 0 -> 1: success */
-	/* Undo increment (but don't miss wakeup) */
-	if(adec(&l->key) == 0)
-		return 0;	/* changed from 1 -> 0: no contention */
-	_SEMRELEASE(&l->sem, 1);
-	return 0;
+	lk->val = 0;
 }