kern/{condition,mutex}: refactor common code

The condition module intrusively uses mutexes. Augment the interface of
the mutex module so that mutexes and conditions share common code. As a
side effect, the implementation should have gained in clarity.

1 files changed, 115 insertions, 0 deletions

diff --git a/kern/mutex_i.h b/kern/mutex_i.h
new file mode 100644
index 00000000..2fa5cb42
--- /dev/null
+++ b/kern/mutex_i.h
@@ -0,0 +1,115 @@
+/*
+ * Copyright (c) 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/>.
+ */
+
+#ifndef _KERN_MUTEX_I_H
+#define _KERN_MUTEX_I_H
+
+#include <kern/assert.h>
+#include <kern/list.h>
+#include <kern/spinlock.h>
+#include <kern/thread.h>
+#include <machine/atomic.h>
+
+#define MUTEX_UNLOCKED  0
+#define MUTEX_LOCKED    1
+#define MUTEX_CONTENDED 2
+
+struct mutex_waiter {
+    struct list node;
+    struct thread *thread;
+};
+
+struct mutex {
+    unsigned long state;
+    struct spinlock lock;
+    struct list waiters;
+};
+
+void mutex_lock_slow(struct mutex *mutex);
+
+void mutex_unlock_slow(struct mutex *mutex);
+
+static inline unsigned long
+mutex_tryacquire(struct mutex *mutex)
+{
+    return atomic_cas(&mutex->state, MUTEX_UNLOCKED, MUTEX_LOCKED);
+}
+
+static inline unsigned long
+mutex_tryacquire_slow(struct mutex *mutex)
+{
+    return atomic_swap(&mutex->state, MUTEX_CONTENDED);
+}
+
+static inline unsigned long
+mutex_release(struct mutex *mutex)
+{
+    unsigned long state;
+
+    state = atomic_swap(&mutex->state, MUTEX_UNLOCKED);
+    assert((state == MUTEX_LOCKED) || (state == MUTEX_CONTENDED));
+    return state;
+}
+
+static inline void
+mutex_queue(struct mutex *mutex, struct mutex_waiter *waiter)
+{
+    list_insert_tail(&mutex->waiters, &waiter->node);
+}
+
+static inline void
+mutex_queue_list(struct mutex *mutex, struct list *waiters)
+{
+    list_concat(&mutex->waiters, waiters);
+}
+
+static inline void
+mutex_wait(struct mutex *mutex, struct mutex_waiter *waiter)
+{
+    unsigned long state;
+
+    do {
+        thread_sleep(&mutex->lock);
+        state = mutex_tryacquire_slow(mutex);
+    } while (state != MUTEX_UNLOCKED);
+
+    list_remove(&waiter->node);
+}
+
+static inline void
+mutex_signal(struct mutex *mutex)
+{
+    struct mutex_waiter *waiter;
+
+    if (!list_empty(&mutex->waiters)) {
+        waiter = list_first_entry(&mutex->waiters, struct mutex_waiter, node);
+        thread_wakeup(waiter->thread);
+    }
+}
+
+static inline void
+mutex_trydowngrade(struct mutex *mutex)
+{
+    if (list_empty(&mutex->waiters)) {
+        unsigned long state;
+
+        state = atomic_swap(&mutex->state, MUTEX_LOCKED);
+        assert(state == MUTEX_CONTENDED);
+    }
+}
+
+#endif /* _KERN_MUTEX_I_H */