git: 9front

Info  •  Files  •  Log  •  Branches

cwfs: use atomic compare and swap to avoid semacquire() syscalls in new queue implementation

--- a/sys/src/cmd/cwfs/sub.c

+++ b/sys/src/cmd/cwfs/sub.c

@@ -917,12 +917,17 @@

 		fprint(2, "%s\n", s1);

 }

+extern int cas(long *p, long ov, long nv);

+

 void*

 fs_recv(Queue *q, int)

 {

 	void *a;

+	long v;

-	semacquire(&q->count, 1);

+	v = q->count;

+	if(v == 0 || cas(&q->count, v, v-1) == 0)

+		semacquire(&q->count, 1);

 	lock(&q->rl);

 	a = *q->rp;

 	if(++q->rp >= &q->args[q->size])

@@ -935,7 +940,11 @@

 void

 fs_send(Queue *q, void *a)

 {

-	semacquire(&q->avail, 1);

+	long v;

+

+	v = q->avail;

+	if(v == 0 || cas(&q->avail, v, v-1) == 0)

+		semacquire(&q->avail, 1);

 	lock(&q->wl);

 	*q->wp = a;

 	if(++q->wp >= &q->args[q->size])

-- 

⑨