From: Kirk McKusick <mckusick@ucbvax.Berkeley.EDU>
Date: Sun, 14 May 1995 02:26:04 +0000 (-0800)
Subject: add simple locking primitives
X-Git-Url: https://git.subgeniuskitty.com/unix-history/.git/commitdiff_plain/702e05af62eec122ec1dbc4dda257e49f8e1bf6a

add simple locking primitives

SCCS-vsn: sys/hp300/include/param.h 8.3
---

diff --git a/usr/src/sys/hp300/include/param.h b/usr/src/sys/hp300/include/param.h
index d1a632276e..781cfac02c 100644
--- a/usr/src/sys/hp300/include/param.h
+++ b/usr/src/sys/hp300/include/param.h
@@ -18,6 +18,7 @@
  * Machine dependent constants for HP9000 series 300.
  */
 #define	MACHINE "hp300"
+#define NCPUS	1
 
 /*
  * Round p (pointer or byte index) up to a correctly-aligned value for all
@@ -173,3 +174,59 @@ int	cpuspeed;
 #define HPMMBASEADDR(v) \
 	((unsigned)(v) & ~HPMMMASK)
 #endif
+
+/*
+ * A simple spin lock.
+ *
+ * This structure only sets one bit of data, but is sized based on the
+ * minimum word size that can be operated on by the hardware test-and-set
+ * instruction. It is only needed for multiprocessors, as uniprocessors
+ * will always run to completion or a sleep. It is an error to hold one
+ * of these locks while a process is sleeping.
+ */
+struct simplelock {
+	int	lock_data;
+};
+
+#if !defined(DEBUG) && NCPUS > 1
+/*
+ * The simple-lock routines are the primitives out of which the lock
+ * package is built. The machine-dependent code must implement an
+ * atomic test_and_set operation that indivisibly sets the simple lock
+ * to non-zero and returns its old value. It also assumes that the
+ * setting of the lock to zero below is indivisible. Simple locks may
+ * only be used for exclusive locks.
+ */
+static __inline void
+simple_lock_init(lkp)
+	struct simplelock *lkp;
+{
+
+	lkp->lock_data = 0;
+}
+
+static __inline void
+simple_lock(lkp)
+	__volatile struct simplelock *lkp;
+{
+
+	while (test_and_set(&lkp->lock_data))
+		continue;
+}
+
+static __inline int
+simple_lock_try(lkp)
+	__volatile struct simplelock *lkp;
+{
+
+	return (!test_and_set(&lkp->lock_data))
+}
+
+static __inline void
+simple_unlock(lkp)
+	__volatile struct simplelock *lkp;
+{
+
+	lkp->lock_data = 0;
+}
+#endif /* NCPUS > 1 */