kern/rtmutex: new module

The rtmutex provides real-time mutexes, i.e. mutexes for which priority
inheritance is unconditionally enabled.

1 files changed, 111 insertions, 0 deletions

diff --git a/kern/rtmutex.h b/kern/rtmutex.h
new file mode 100644
index 00000000..f7cee716
--- /dev/null
+++ b/kern/rtmutex.h
@@ -0,0 +1,111 @@
+/*
+ * Copyright (c) 2017 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/>.
+ *
+ *
+ * Real-time mutual exclusion locks.
+ *
+ * A real-time mutex is similar to a regular mutex, except priority
+ * inheritance is unconditionnally enabled.
+ */
+
+#ifndef _KERN_RTMUTEX_H
+#define _KERN_RTMUTEX_H
+
+#include <stdint.h>
+
+#include <kern/assert.h>
+#include <kern/error.h>
+#include <kern/rtmutex_i.h>
+#include <kern/rtmutex_types.h>
+
+struct rtmutex;
+
+#define rtmutex_assert_locked(rtmutex) assert((rtmutex)->owner != 0)
+
+/*
+ * Initialize a real-time mutex.
+ */
+static inline void
+rtmutex_init(struct rtmutex *rtmutex)
+{
+    rtmutex->owner = 0;
+}
+
+/*
+ * Attempt to lock the given real-time mutex.
+ *
+ * This function may not sleep.
+ *
+ * Return 0 on success, ERROR_BUSY if the mutex is already locked.
+ */
+static inline int
+rtmutex_trylock(struct rtmutex *rtmutex)
+{
+    uintptr_t prev_owner;
+
+    prev_owner = rtmutex_tryacquire(rtmutex);
+
+    if (prev_owner == 0) {
+        return 0;
+    }
+
+    return ERROR_BUSY;
+}
+
+/*
+ * Lock a real-time mutex.
+ *
+ * If the mutex is already locked, the calling thread sleeps until the
+ * mutex is unlocked, and its priority is propagated as needed to prevent
+ * unbounded priority inversion.
+ *
+ * A mutex can only be locked once.
+ */
+static inline void
+rtmutex_lock(struct rtmutex *rtmutex)
+{
+    uintptr_t prev_owner;
+
+    prev_owner = rtmutex_tryacquire(rtmutex);
+
+    if (prev_owner == 0) {
+        return;
+    }
+
+    rtmutex_lock_slow(rtmutex);
+}
+
+/*
+ * Unlock a real-time mutex.
+ *
+ * The mutex must be locked, and must have been locked by the calling
+ * thread.
+ */
+static inline void
+rtmutex_unlock(struct rtmutex *rtmutex)
+{
+    uintptr_t prev_owner;
+
+    prev_owner = rtmutex_tryrelease(rtmutex);
+
+    if (!(prev_owner & RTMUTEX_CONTENDED)) {
+        return;
+    }
+
+    rtmutex_unlock_slow(rtmutex);
+}
+
+#endif /* _KERN_RTMUTEX_H */