kern/spinlock: add interrupt-handling locking primitives

1 files changed, 60 insertions, 0 deletions

diff --git a/kern/spinlock_i.h b/kern/spinlock_i.h
new file mode 100644
index 00000000..58af6bf1
--- /dev/null
+++ b/kern/spinlock_i.h
@@ -0,0 +1,60 @@
+/*
+ * Copyright (c) 2012, 2013 Richard Braun.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *
+ * This implementation relies on the availability of hardware compare-and-swap
+ * support. It means that almost all spinlock operations imply a full memory
+ * barrier. Users must not rely on this behaviour as it could change in the
+ * future.
+ */
+
+#ifndef _KERN_SPINLOCK_I_H
+#define _KERN_SPINLOCK_I_H
+
+#include <kern/assert.h>
+#include <machine/atomic.h>
+#include <machine/cpu.h>
+
+struct spinlock {
+    unsigned long locked;
+};
+
+/*
+ * Return true if acquired, false if busy.
+ */
+static inline int
+spinlock_tryacquire(struct spinlock *lock)
+{
+    return !atomic_cas(&lock->locked, 0, 1);
+}
+
+static inline void
+spinlock_acquire(struct spinlock *lock)
+{
+    while (!spinlock_tryacquire(lock))
+        cpu_pause();
+}
+
+static inline void
+spinlock_release(struct spinlock *lock)
+{
+    unsigned long locked;
+
+    locked = atomic_swap(&lock->locked, 0);
+    assert(locked);
+}
+
+#endif /* _KERN_SPINLOCK_I_H */