libc: change tas/sleep locks to cas/semacquire/semrelease locks (from sources)

spinlocks have been changed to use the new semacquire/semrelease
syscalls in combination with atomic compare and swap operations.

1 files changed, 20 insertions, 28 deletions

diff --git a/sys/src/libc/port/lock.c b/sys/src/libc/port/lock.c
index af07b9cc7..213fcd778 100644
--- a/sys/src/libc/port/lock.c
+++ b/sys/src/libc/port/lock.c
@@ -2,40 +2,32 @@
 #include <libc.h>
 
 void
-lock(Lock *lk)
+lock(Lock *l)
 {
-	int i;
-
-	/* once fast */
-	if(!_tas(&lk->val))
-		return;
-	/* a thousand times pretty fast */
-	for(i=0; i<1000; i++){
-		if(!_tas(&lk->val))
-			return;
-		sleep(0);
-	}
-	/* now nice and slow */
-	for(i=0; i<1000; i++){
-		if(!_tas(&lk->val))
-			return;
-		sleep(100);
+	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 */
 	}
-	/* take your time */
-	while(_tas(&lk->val))
-		sleep(1000);
 }
 
-int
-canlock(Lock *lk)
+void
+unlock(Lock *l)
 {
-	if(_tas(&lk->val))
-		return 0;
-	return 1;
+	if(adec(&l->key) == 0)
+		return;	/* changed from 1 -> 0: no contention */
+	semrelease(&l->sem, 1);
 }
 
-void
-unlock(Lock *lk)
+int
+canlock(Lock *l)
 {
-	lk->val = 0;
+	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;
 }