[ltt-dev] [RFC PATCH 4/7] urcu:implement URCU_WAIT_READER

[Lai Jiangshan]

synchronize_rcu() find out ongoing readers and wait for them

Signed-off-by: Lai Jiangshan <laijs at cn.fujitsu.com>
---
 urcu.c             |   49 +++++++++++++++++++++++++++++++++++++++++++++++++
 urcu/static/urcu.h |   42 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 91 insertions(+), 0 deletions(-)

diff --git a/urcu.c b/urcu.c
index bd54467..c13be67 100644
--- a/urcu.c
+++ b/urcu.c
@@ -419,6 +419,53 @@ static void urcu_sync_unlock_if_not_proxy_unlocked(int32_t *lock, int32_t self)
 		urcu_sync_slow_unlock(lock);
 }
 
+/* also implies mb() */
+void __urcu_read_unlock_specail(void)
+{
+	urcu_sync_unlock_if_not_proxy_unlocked(&rcu_reader.sync,
+			rcu_reader.tid);
+}
+
+/*
+ * synchronize_rcu		rcu_read_unlock(outmost)
+ *
+ *
+ * sync = tid;			ctr = 0;
+ * smp_mb_master();		smp_mb_slave();
+ * test ctr and wait;		test sync and wakeup;
+ */
+
+void synchronize_rcu(void)
+{
+	struct rcu_reader *index;
+	int32_t self = syscall(SYS_gettid);
+
+	mutex_lock(&rcu_gp_lock);
+
+	if (cds_list_empty(&registry))
+		goto out;
+
+	cds_list_for_each_entry(index, &registry, node)
+		urcu_sync_proxy_lock(&index->sync, index->tid);
+
+	smp_mb_master(RCU_MB_GROUP);
+
+	cds_list_for_each_entry(index, &registry, node) {
+		if (_CMM_LOAD_SHARED(index->ctr) == 0) {
+			urcu_sync_proxy_unlock(&index->sync);
+		} else {
+			/* reader still running, we need to wait reader */
+			urcu_sync_lock(&index->sync, self);
+			urcu_sync_unlock(&index->sync, self);
+		}
+	}
+
+	/* ensure rcu_read_unlock() finish when we found the ctr==0 */
+	smp_mb_master(RCU_MB_GROUP); /* ensure rcu_read_unlock() finish */
+
+out:
+	mutex_unlock(&rcu_gp_lock);
+}
 #endif /* #else #ifndef URCU_WAIT_READER */
 
 /*
@@ -437,7 +484,9 @@ void rcu_read_unlock(void)
 
 void rcu_register_thread(void)
 {
+	rcu_reader.tid = syscall(SYS_gettid);
 	rcu_reader.pthread = pthread_self();
+	rcu_reader.sync = 0;
 	assert(rcu_reader.need_mb == 0);
 	assert(!(rcu_reader.ctr & RCU_GP_CTR_NEST_MASK));
 
diff --git a/urcu/static/urcu.h b/urcu/static/urcu.h
index 32d1af8..0941fd2 100644
--- a/urcu/static/urcu.h
+++ b/urcu/static/urcu.h
@@ -221,9 +221,11 @@ static inline void smp_mb_slave(int group)
 struct rcu_reader {
 	/* Data used by both reader and synchronize_rcu() */
 	unsigned long ctr;
+	int32_t sync;
 	char need_mb;
 	/* Data used for registry */
 	struct cds_list_head node __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
+	pid_t tid;
 	pthread_t pthread;
 };
 
@@ -313,6 +315,46 @@ static inline int32_t urcu_sync_lock_onwer(int32_t *lock)
 	return _CMM_LOAD_SHARED(*lock) & ~FUTEX_WAITERS;
 }
 
+void __urcu_read_unlock_specail(void);
+
+static inline void _rcu_read_lock(void)
+{
+	unsigned long tmp;
+
+	cmm_barrier();
+	tmp = rcu_reader.ctr;
+
+	if (!tmp) {
+		_CMM_STORE_SHARED(rcu_reader.ctr, 1);
+		smp_mb_slave(RCU_MB_GROUP);
+	} else {
+		_CMM_STORE_SHARED(rcu_reader.ctr, tmp + 1);
+		cmm_barrier();
+	}
+}
+
+static inline void _rcu_read_unlock(void)
+{
+	unsigned long tmp;
+
+	cmm_barrier();
+	tmp = rcu_reader.ctr;
+
+	if (tmp == 1) {
+		smp_mb_slave(RCU_MB_GROUP);
+
+		rcu_reader.ctr = 0;
+		smp_mb_slave(RCU_MB_GROUP);
+
+		if (unlikely(urcu_sync_lock_onwer(&rcu_reader.sync)
+				== rcu_reader.tid))
+			__urcu_read_unlock_specail();
+	} else {
+		_CMM_STORE_SHARED(rcu_reader.ctr, tmp - 1);
+		cmm_barrier();
+	}
+}
+
 #endif /* #else #ifndef URCU_WAIT_READER */
 
 #ifdef __cplusplus
-- 
1.7.4.4