[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 <la...@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


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