patch-2.4.0-test3 linux/lib/dec_and_lock.c

• Lines: 38
• Date: Fri Jul 7 16:22:48 2000
• Orig file: v2.4.0-test2/linux/lib/dec_and_lock.c
• Orig date: Wed Dec 31 16:00:00 1969

diff -u --recursive --new-file v2.4.0-test2/linux/lib/dec_and_lock.c linux/lib/dec_and_lock.c
@@ -0,0 +1,37 @@
+#include <linux/spinlock.h>
+#include <asm/atomic.h>
+
+/*
+ * This is an architecture-neutral, but slow,
+ * implementation of the notion of "decrement
+ * a reference count, and return locked if it
+ * decremented to zero".
+ *
+ * NOTE NOTE NOTE! This is _not_ equivalent to
+ *
+ *	if (atomic_dec_and_test(&atomic)) {
+ *		spin_lock(&lock);
+ *		return 1;
+ *	}
+ *	return 0;
+ *
+ * because the spin-lock and the decrement must be
+ * "atomic".
+ *
+ * This slow version gets the spinlock unconditionally,
+ * and releases it if it isn't needed. Architectures
+ * are encouraged to come up with better approaches,
+ * this is trivially done efficiently using a load-locked
+ * store-conditional approach, for example.
+ */
+
+#ifndef atomic_dec_and_lock
+int atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
+{
+	spin_lock(lock);
+	if (atomic_dec_and_test(atomic))
+		return 1;
+	spin_unlock(lock);
+	return 0;
+}
+#endif