a

libc/lock.c

@@ -0,0 +1,64 @@
+#include <u.h>
+#include <libc.h>
+
+int
+canlock(Lock *lk)
+{
+	return !tas(&lk->key);
+}
+
+void
+lock(Lock *lk)
+{
+	int i;
+
+	/* easy case */
+	if(canlock(lk))
+		return;
+
+	/* for multi processor machines */
+	for(i=0; i<100; i++)
+		if(canlock(lk))
+			return;
+
+	for(i=0; i<100; i++) {
+		osyield(0);
+		if(canlock(lk))
+			return;
+	}
+
+	/* looking bad - make sure it is not a priority problem */
+	for(i=0; i<12; i++) {
+		osmsleep(1<<i);
+		if(canlock(lk))
+			return;
+	}
+
+	/* we are in trouble */
+	for(;;) {
+		if(canlock(lk))
+			return;
+		iprint("lock loop %ld: val=%d &lock=%ux pc=%ux\n", getpid(), lk->key, lk, getcallerpc(&lk));
+		osmsleep(1000);
+	}
+}
+
+void
+unlock(Lock *lk)
+{
+	assert(lk->key);
+	lk->key = 0;
+}
+
+void
+ilock(Lock *lk)
+{
+	lock(lk);
+}
+
+void
+iunlock(Lock *lk)
+{
+	unlock(lk);
+}
+