Add rcu_read_ongoing() API to each urcu flavor

[urcu.git] / urcu / static / urcu-qsbr.h

diff --git a/urcu/static/urcu-qsbr.h b/urcu/static/urcu-qsbr.h
index c8a87b8d777a7ce0bcae127a5d1bd1545bfee561..ea5e13adebd5fae0374a5ad81693dd6cf46436c2 100644 (file)
--- a/urcu/static/urcu-qsbr.h
+++ b/urcu/static/urcu-qsbr.h
@@ -62,6 +62,12 @@ extern "C" {
 #define rcu_assert(args...)
 #endif
 
+enum rcu_state {
+       RCU_READER_ACTIVE_CURRENT,
+       RCU_READER_ACTIVE_OLD,
+       RCU_READER_INACTIVE,
+};
+
 #ifdef DEBUG_YIELD
 #include <sched.h>
 #include <time.h>
@@ -149,12 +155,16 @@ static inline void wake_up_gp(void)
        }
 }
 
-static inline int rcu_gp_ongoing(unsigned long *ctr)
+static inline enum rcu_state rcu_reader_state(unsigned long *ctr)
 {
        unsigned long v;
 
        v = CMM_LOAD_SHARED(*ctr);
-       return v && (v != rcu_gp_ctr);
+       if (!v)
+               return RCU_READER_INACTIVE;
+       if (v == rcu_gp_ctr)
+               return RCU_READER_ACTIVE_CURRENT;
+       return RCU_READER_ACTIVE_OLD;
 }
 
 /*
@@ -181,21 +191,56 @@ static inline void _rcu_read_unlock(void)
 }
 
 /*
- * Inform RCU of a quiescent state.
+ * Returns whether within a RCU read-side critical section.
  *
  * This function is less than 10 lines long.  The intent is that this
  * function meets the 10-line criterion for LGPL, allowing this function
  * to be invoked directly from non-LGPL code.
  */
-static inline void _rcu_quiescent_state(void)
+static inline int _rcu_read_ongoing(void)
+{
+       return URCU_TLS(rcu_reader).ctr;
+}
+
+/*
+ * This is a helper function for _rcu_quiescent_state().
+ * The first cmm_smp_mb() ensures memory accesses in the prior read-side
+ * critical sections are not reordered with store to
+ * URCU_TLS(rcu_reader).ctr, and ensures that mutexes held within an
+ * offline section that would happen to end with this
+ * rcu_quiescent_state() call are not reordered with
+ * store to URCU_TLS(rcu_reader).ctr.
+ */
+static inline void _rcu_quiescent_state_update_and_wakeup(unsigned long gp_ctr)
 {
        cmm_smp_mb();
-       _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, _CMM_LOAD_SHARED(rcu_gp_ctr));
+       _CMM_STORE_SHARED(URCU_TLS(rcu_reader).ctr, gp_ctr);
        cmm_smp_mb();   /* write URCU_TLS(rcu_reader).ctr before read futex */
        wake_up_gp();
        cmm_smp_mb();
 }
 
+/*
+ * Inform RCU of a quiescent state.
+ *
+ * This function is less than 10 lines long.  The intent is that this
+ * function meets the 10-line criterion for LGPL, allowing this function
+ * to be invoked directly from non-LGPL code.
+ *
+ * We skip the memory barriers and gp store if our local ctr already
+ * matches the global rcu_gp_ctr value: this is OK because a prior
+ * _rcu_quiescent_state() or _rcu_thread_online() already updated it
+ * within our thread, so we have no quiescent state to report.
+ */
+static inline void _rcu_quiescent_state(void)
+{
+       unsigned long gp_ctr;
+
+       if ((gp_ctr = CMM_LOAD_SHARED(rcu_gp_ctr)) == URCU_TLS(rcu_reader).ctr)
+               return;
+       _rcu_quiescent_state_update_and_wakeup(gp_ctr);
+}
+
 /*
  * Take a thread offline, prohibiting it from entering further RCU
  * read-side critical sections.