X-Git-Url: https://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu.c;h=e93170d749b4c939884840767febcc3e3d820997;hp=6e9589145cf789a06c00aa988cb01d8c3dcb27fa;hb=2dfb8b5e30bc2d268bcbc57eceb9c54d21b36d90;hpb=6abb4bd53503c325dc94b0c0f60b44b9550b462f

diff --git a/urcu.c b/urcu.c
index 6e95891..e93170d 100644
--- a/urcu.c
+++ b/urcu.c
@@ -120,14 +120,6 @@ static void mutex_unlock(pthread_mutex_t *mutex)
 	}
 }
 
-/*
- * called with rcu_gp_lock held.
- */
-static void switch_next_rcu_qparity(void)
-{
-	STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE);
-}
-
 #ifdef RCU_MEMBARRIER
 static void smp_mb_heavy(void)
 {
@@ -207,14 +199,29 @@ static void wait_gp(void)
 		      NULL, NULL, 0);
 }
 
-void wait_for_quiescent_state(void)
+void update_counter_and_wait(void)
 {
 	LIST_HEAD(qsreaders);
 	int wait_loops = 0;
 	struct rcu_reader *index, *tmp;
 
-	if (list_empty(&registry))
-		return;
+	/* Switch parity: 1 -> 0, 0 -> 1 */
+	STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE);
+
+	/*
+	 * Must commit qparity update to memory before waiting for other parity
+	 * quiescent state. Failure to do so could result in the writer waiting
+	 * forever while new readers are always accessing data (no progress).
+	 * Ensured by STORE_SHARED and LOAD_SHARED.
+	 */
+
+	/*
+	 * Adding a smp_mb() which is _not_ formally required, but makes the
+	 * model easier to understand. It does not have a big performance impact
+	 * anyway, given this is the write-side.
+	 */
+	smp_mb();
+
 	/*
 	 * Wait for each thread rcu_reader.ctr count to become 0.
 	 */
@@ -280,33 +287,19 @@ void synchronize_rcu(void)
 {
 	mutex_lock(&rcu_gp_lock);
 
+	if (list_empty(&registry))
+		goto out;
+
 	/* All threads should read qparity before accessing data structure
 	 * where new ptr points to. Must be done within rcu_gp_lock because it
 	 * iterates on reader threads.*/
 	/* Write new ptr before changing the qparity */
 	smp_mb_heavy();
 
-	switch_next_rcu_qparity();	/* 0 -> 1 */
-
-	/*
-	 * Must commit qparity update to memory before waiting for parity
-	 * 0 quiescent state. Failure to do so could result in the writer
-	 * waiting forever while new readers are always accessing data (no
-	 * progress).
-	 * Ensured by STORE_SHARED and LOAD_SHARED.
-	 */
-
-	/*
-	 * Adding a smp_mb() which is _not_ formally required, but makes the
-	 * model easier to understand. It does not have a big performance impact
-	 * anyway, given this is the write-side.
-	 */
-	smp_mb();
-
 	/*
 	 * Wait for previous parity to be empty of readers.
 	 */
-	wait_for_quiescent_state();	/* Wait readers in parity 0 */
+	update_counter_and_wait();	/* 0 -> 1, wait readers in parity 0 */
 
 	/*
 	 * Must finish waiting for quiescent state for parity 0 before
@@ -323,33 +316,16 @@ void synchronize_rcu(void)
 	 */
 	smp_mb();
 
-	switch_next_rcu_qparity();	/* 1 -> 0 */
-
-	/*
-	 * Must commit qparity update to memory before waiting for parity
-	 * 1 quiescent state. Failure to do so could result in the writer
-	 * waiting forever while new readers are always accessing data (no
-	 * progress).
-	 * Ensured by STORE_SHARED and LOAD_SHARED.
-	 */
-
-	/*
-	 * Adding a smp_mb() which is _not_ formally required, but makes the
-	 * model easier to understand. It does not have a big performance impact
-	 * anyway, given this is the write-side.
-	 */
-	smp_mb();
-
 	/*
 	 * Wait for previous parity to be empty of readers.
 	 */
-	wait_for_quiescent_state();	/* Wait readers in parity 1 */
+	update_counter_and_wait();	/* 1 -> 0, wait readers in parity 1 */
 
 	/* Finish waiting for reader threads before letting the old ptr being
 	 * freed. Must be done within rcu_gp_lock because it iterates on reader
 	 * threads. */
 	smp_mb_heavy();
-
+out:
 	mutex_unlock(&rcu_gp_lock);
 }