From b2cfc4e2e71d0f0a5113ddfbd93c8285cc4d74e4 Mon Sep 17 00:00:00 2001
From: rsc <devnull@localhost>
Date: Tue, 30 Sep 2003 17:47:41 +0000
Subject: Initial revision

---
 src/lib9/lock.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)
 create mode 100644 src/lib9/lock.c

(limited to 'src/lib9/lock.c')

diff --git a/src/lib9/lock.c b/src/lib9/lock.c
new file mode 100644
index 00000000..2da73626
--- /dev/null
+++ b/src/lib9/lock.c
@@ -0,0 +1,54 @@
+#include <unistd.h>
+#include <sched.h>
+#include <lib9.h>
+
+int _ntas;
+static int
+_xtas(void *v)
+{
+	int x;
+
+_ntas++;
+	x = _tas(v);
+	if(x == 0 || x == 0xCAFEBABE)
+		return x;
+	fprint(2, "%d: tas %p got %ux\n", getpid(), v, x);
+	abort();
+}
+
+int
+canlock(Lock *l)
+{
+	return !_xtas(&l->val);
+}
+
+void
+unlock(Lock *l)
+{
+	l->val = 0;
+}
+
+void
+lock(Lock *lk)
+{
+	int i;
+
+	/* once fast */
+	if(!_xtas(&lk->val))
+		return;
+	/* a thousand times pretty fast */
+	for(i=0; i<1000; i++){
+		if(!_xtas(&lk->val))
+			return;
+		sched_yield();
+	}
+	/* now nice and slow */
+	for(i=0; i<1000; i++){
+		if(!_xtas(&lk->val))
+			return;
+		usleep(100*1000);
+	}
+	/* take your time */
+	while(_xtas(&lk->val))
+		usleep(1000*1000);
+}
-- 
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