1 files changed, 98 insertions, 0 deletions
diff --git a/kern/spinlock.h b/kern/spinlock.h
new file mode 100644
index 00000000..1169900e
--- /dev/null
+++ b/kern/spinlock.h
@@ -0,0 +1,98 @@
+/*
+ * Copyright (c) 2012 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/>.
+ *
+ *
+ * Spin lock.
+ *
+ * This implementation relies on the availability of hardware compare-and-swap
+ * support. In addition, spin locks are reserved for the special cases where
+ * a critical section must work in every context (thread, interrupt, or even
+ * during early boot). As a result, interrupts are disabled when a spin lock
+ * is acquired.
+ */
+
+#ifndef _KERN_SPINLOCK_H
+#define _KERN_SPINLOCK_H
+
+#include <machine/atomic.h>
+#include <machine/cpu.h>
+
+struct spinlock {
+    unsigned long locked;
+};
+
+/*
+ * Static spin lock initializer.
+ */
+#define SPINLOCK_INITIALIZER { 0 }
+
+/*
+ * Initialize a spin lock.
+ */
+static inline void
+spinlock_init(struct spinlock *lock)
+{
+    lock->locked = 0;
+}
+
+/*
+ * Attempt to acquire a spin lock.
+ *
+ * Return false if acquired, true if busy.
+ */
+static inline int
+spinlock_trylock(struct spinlock *lock, unsigned long *flagsp)
+{
+    unsigned long flags, locked;
+
+    flags = cpu_intr_save();
+    locked = atomic_cas(&lock->locked, 0, 1);
+
+    if (locked)
+        cpu_intr_restore(flags);
+    else
+        *flagsp = flags;
+
+    return locked;
+}
+
+/*
+ * Acquire a spin lock.
+ */
+static inline unsigned long
+spinlock_lock(struct spinlock *lock)
+{
+    unsigned long flags;
+
+    flags = cpu_intr_save();
+
+    while (atomic_cas(&lock->locked, 0, 1))
+        cpu_pause();
+
+    return flags;
+}
+
+/*
+ * Release a spin lock.
+ */
+static inline void
+spinlock_unlock(struct spinlock *lock, unsigned long flags)
+{
+    atomic_swap(&lock->locked, 0);
+    cpu_intr_restore(flags);
+}
+
+#endif /* _KERN_SPINLOCK_H */