fat-rwlock: New big but fast synchronization primitive.

[sliver-openvswitch.git] / lib / fat-rwlock.h

diff --git a/lib/fat-rwlock.h b/lib/fat-rwlock.h
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+/*
+ * Copyright (c) 2013, 2014 Nicira, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FAT_RWLOCK_H
+#define FAT_RWLOCK_H 1
+
+#include "compiler.h"
+#include "list.h"
+#include "ovs-thread.h"
+
+/* "Fat rwlock".
+ *
+ * This implements a reader-writer lock that uses a lot of memory (128 to 192
+ * bytes per thread that takes the lock) but avoids cache line bouncing when
+ * taking the read side.  Thus, a fat_rwlock is a good choice for rwlocks taken
+ * frequently by readers.
+ */
+struct OVS_LOCKABLE fat_rwlock {
+    ovsthread_key_t key;
+
+    /* Contains "struct fat_rwlock_slot"s, one for each thread that has taken
+     * this lock.  Guarded by 'mutex'. */
+    struct list threads OVS_GUARDED;
+    struct ovs_mutex mutex;
+};
+
+void fat_rwlock_init(struct fat_rwlock *);
+void fat_rwlock_destroy(struct fat_rwlock *);
+
+void fat_rwlock_rdlock(const struct fat_rwlock *rwlock) OVS_ACQ_RDLOCK(rwlock);
+int fat_rwlock_tryrdlock(const struct fat_rwlock *rwlock)
+    OVS_TRY_RDLOCK(0, rwlock);
+void fat_rwlock_wrlock(const struct fat_rwlock *rwlock) OVS_ACQ_WRLOCK(rwlock);
+void fat_rwlock_unlock(const struct fat_rwlock *rwlock) OVS_RELEASES(rwlock);
+
+#endif /* fat-rwlock.h */