lib: implementation of read/write locks

This adds read/write locks, allowing for concurrent reads on the locked
datastructure. This is needed for the fast path.

1 files changed, 125 insertions, 0 deletions

diff --git a/src/lib/rw_lock.c b/src/lib/rw_lock.c
new file mode 100644
index 00000000..cf471e60
--- /dev/null
+++ b/src/lib/rw_lock.c
@@ -0,0 +1,125 @@
+/*
+ * Ouroboros - Copyright (C) 2016
+ *
+ * Read/Write locks
+ *
+ *    Dimitri Staessens <dimitri.staessens@intec.ugent.be>
+ *
+ * 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 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, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <ouroboros/rw_lock.h>
+
+int rw_lock_init(rw_lock_t * lock)
+{
+        if (lock == NULL)
+                return -1;
+
+        pthread_mutex_init(&lock->lock, NULL);
+        pthread_mutex_init(&lock->i_lock, NULL);
+        lock->i = 0;
+
+        return 0;
+}
+
+void rw_lock_destroy(rw_lock_t * lock)
+{
+        if (lock == NULL)
+                return;
+
+        pthread_mutex_destroy(&lock->lock);
+        pthread_mutex_destroy(&lock->i_lock);
+        lock->i = -1;
+}
+
+int rw_lock_rdlock(rw_lock_t * lock)
+{
+        int ret = 0;
+
+        if (lock == NULL)
+                return -1;
+
+        pthread_mutex_lock(&lock->i_lock);
+
+        if (lock->i < 0) {
+                pthread_mutex_unlock(&lock->i_lock);
+                return -1;
+        }
+
+        if (lock->i == 0)
+                ret = pthread_mutex_lock(&lock->lock);
+
+        ++(lock->i);
+
+        pthread_mutex_unlock(&lock->i_lock);
+
+        return ret;
+}
+
+int rw_lock_wrlock(rw_lock_t * lock)
+{
+        if (lock == NULL)
+                return -1;
+
+        pthread_mutex_lock(&lock->i_lock);
+
+        if (lock->i < 0) {
+                pthread_mutex_unlock(&lock->i_lock);
+                return -1;
+        }
+
+        pthread_mutex_unlock(&lock->i_lock);
+
+        while (1) {
+                pthread_mutex_lock(&lock->i_lock);
+
+                if (lock->i == 0) {
+                        pthread_mutex_unlock(&lock->i_lock);
+                        break;
+                }
+
+                pthread_mutex_unlock(&lock->i_lock);
+
+                sched_yield();
+        }
+
+        ++(lock->i);
+
+        return pthread_mutex_lock(&lock->lock);
+}
+
+int rw_lock_unlock(rw_lock_t * lock)
+{
+        int ret = 0;
+
+        if (lock == NULL)
+                return -1;
+
+        pthread_mutex_lock(&lock->i_lock);
+
+        if (lock->i < 0) {
+                pthread_mutex_unlock(&lock->i_lock);
+                return -1;
+        }
+
+        --(lock->i);
+
+        if (lock->i == 0)
+                ret = pthread_mutex_unlock(&lock->lock);
+
+        pthread_mutex_unlock(&lock->i_lock);
+
+        return ret;
+}