1 files changed, 54 insertions, 0 deletions

diff --git a/firmware/kernel/include/mrsw_lock.h b/firmware/kernel/include/mrsw_lock.h
new file mode 100644
index 0000000000..fbfe1d405d
--- /dev/null
+++ b/firmware/kernel/include/mrsw_lock.h
@@ -0,0 +1,54 @@
+/***************************************************************************
+ *             __________               __   ___.
+ *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
+ *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
+ *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
+ *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
+ *                     \/            \/     \/    \/            \/
+ * $Id$
+ *
+ * Copyright (C) 2014 by Michael Sevakis
+ *
+ * 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 2
+ * of the License, or (at your option) any later version.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ****************************************************************************/
+#ifndef MRSW_LOCK_H
+#define MRSW_LOCK_H
+
+/* Multi-reader, single-writer object that allows mutltiple readers or a
+ * single writer thread access to a critical section.
+ *
+ * Readers and writers, as with a mutex, may claim the lock recursively for
+ * the same type of access they were already granted.
+ *
+ * Writers are trivially granted read access by ignoring the request; the
+ * object is not changed.
+ *
+ * Reader promotion to writer is NOT supported and a reader attempting write
+ * access will result in a deadlock. That could change but for now, be warned.
+ *
+ * Full priority inheritance is implemented.
+ */
+struct mrsw_lock
+{
+    int volatile count; /* rd/wr counter; >0 = reader(s), <0 = writer */
+    struct thread_entry *queue;
+    struct blocker_splay splay; /* priority inheritance info
+                                   for waiters */
+    uint8_t rdrecursion[MAXTHREADS]; /* per-thread reader recursion counts */
+    IF_COP( struct corelock cl; )
+};
+
+void mrsw_init(struct mrsw_lock *mrsw);
+void mrsw_read_acquire(struct mrsw_lock *mrsw);
+void mrsw_read_release(struct mrsw_lock *mrsw);
+void mrsw_write_acquire(struct mrsw_lock *mrsw);
+void mrsw_write_release(struct mrsw_lock *mrsw);
+
+#endif /* MRSW_LOCK_H */