Introducing basic RCU primitives for lock-less shared data structures

1 files changed, 55 insertions, 0 deletions

diff --git a/lib/rcu.h b/lib/rcu.h
new file mode 100644
index 00000000..c537a1ef
--- /dev/null
+++ b/lib/rcu.h
@@ -0,0 +1,55 @@
+/*
+ *	BIRD Library -- Read-Copy-Update Basic Operations
+ *
+ *	(c) 2021 Maria Matejka <mq@jmq.cz>
+ *	(c) 2021 CZ.NIC z.s.p.o.
+ *
+ *	Can be freely distributed and used under the terms of the GNU GPL.
+ *	Note: all the relevant patents shall be expired.
+ */
+
+#ifndef _BIRD_RCU_H_
+#define _BIRD_RCU_H_
+
+#include "lib/birdlib.h"
+#include "lib/lists.h"
+#include <stdatomic.h>
+
+#define RCU_GP_PHASE  0x100000
+#define RCU_NEST_MASK 0x0fffff
+#define RCU_NEST_CNT  0x000001
+
+extern _Atomic uint rcu_gp_ctl;
+
+struct rcu_birdloop {
+  node n;
+  _Atomic uint ctl;
+};
+
+extern _Thread_local struct rcu_birdloop *this_rcu_birdloop;
+
+static inline void rcu_read_lock(void)
+{
+  uint cmp = atomic_load_explicit(&this_rcu_birdloop->ctl, memory_order_acquire);
+
+  if (cmp & RCU_NEST_MASK)
+    atomic_store_explicit(&this_rcu_birdloop->ctl, cmp + RCU_NEST_CNT, memory_order_relaxed);
+  else
+    atomic_store(&this_rcu_birdloop->ctl, atomic_load_explicit(&rcu_gp_ctl, memory_order_acquire));
+}
+
+static inline void rcu_read_unlock(void)
+{
+  atomic_fetch_sub(&this_rcu_birdloop->ctl, RCU_NEST_CNT);
+}
+
+void synchronize_rcu(void);
+
+/* Registering and unregistering a birdloop. To be called from birdloop implementation */
+void rcu_birdloop_start(struct rcu_birdloop *);
+void rcu_birdloop_stop(struct rcu_birdloop *);
+
+/* Run this from resource init */
+void rcu_init(void);
+
+#endif