kern/semaphore: new module

1 files changed, 60 insertions, 0 deletions

diff --git a/kern/semaphore_i.h b/kern/semaphore_i.h
new file mode 100644
index 0000000..c6769c1
--- /dev/null
+++ b/kern/semaphore_i.h
@@ -0,0 +1,60 @@
+/*
+ * 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/>.
+ */
+
+#ifndef _KERN_SEMAPHORE_I_H
+#define _KERN_SEMAPHORE_I_H
+
+#include <kern/assert.h>
+#include <machine/atomic.h>
+
+struct semaphore {
+    unsigned int value;
+};
+
+static inline unsigned int
+semaphore_dec(struct semaphore *semaphore)
+{
+    unsigned int prev, value;
+
+    do {
+        value = semaphore->value;
+
+        if (value == 0) {
+            break;
+        }
+
+        prev = atomic_cas_uint(&semaphore->value, value, value - 1);
+    } while (prev != value);
+
+    return value;
+}
+
+static inline unsigned int
+semaphore_inc(struct semaphore *semaphore)
+{
+    unsigned int prev;
+
+    prev = atomic_fetchadd_uint(&semaphore->value, 1);
+    assert(prev != SEMAPHORE_VALUE_MAX);
+    return prev;
+}
+
+void semaphore_wait_slow(struct semaphore *semaphore);
+
+void semaphore_post_slow(struct semaphore *semaphore);
+
+#endif /* _KERN_SEMAPHORE_I_H */