X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu%2Fstatic%2Furcu-qsbr.h;h=ea5e13adebd5fae0374a5ad81693dd6cf46436c2;hp=c8a87b8d777a7ce0bcae127a5d1bd1545bfee561;hb=882f335739b978d1c55be2faeed077f315afe5d7;hpb=6ff854acfa013195bdb71dddc654ec76a4c296c9

diff --git a/urcu/static/urcu-qsbr.h b/urcu/static/urcu-qsbr.h
index c8a87b8..ea5e13a 100644
--- 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.