Do two parity flip in the writer to fix race condition

[urcu.git] / urcu.c

diff --git a/urcu.c b/urcu.c
index e401d8dc75d34bf04d2e62da56df3cc08f0d470d..1a276ce33663439b7cb128e1ab6bea147faec1ed 100644 (file)
--- a/urcu.c
+++ b/urcu.c
@@ -113,13 +113,35 @@ void wait_for_quiescent_state(int parity)
        force_mb_all_threads();
 }
 
+static void switch_qparity(void)
+{
+       int prev_parity;
+
+       /* All threads should read qparity before accessing data structure. */
+       /* Write ptr before changing the qparity */
+       force_mb_all_threads();
+       prev_parity = switch_next_urcu_qparity();
+
+       /*
+        * Wait for previous parity to be empty of readers.
+        */
+       wait_for_quiescent_state(prev_parity);
+}
+
+void synchronize_rcu(void)
+{
+       rcu_write_lock();
+       switch_qparity();
+       switch_qparity();
+       rcu_write_unlock();
+}
+
 /*
  * Return old pointer, OK to free, no more reference exist.
  * Called under rcu_write_lock.
  */
 void *urcu_publish_content(void **ptr, void *new)
 {
-       int prev_parity;
        void *oldptr;
 
        /*
@@ -134,19 +156,10 @@ void *urcu_publish_content(void **ptr, void *new)
         */
        oldptr = *ptr;
        *ptr = new;
-       /* All threads should read qparity before ptr */
-       /* Write ptr before changing the qparity */
-       force_mb_all_threads();
-       prev_parity = switch_next_urcu_qparity();
 
-       /*
-        * Wait for previous parity to be empty of readers.
-        */
-       wait_for_quiescent_state(prev_parity);
-       /*
-        * Deleting old data is ok !
-        */
-       
+       switch_qparity();
+       switch_qparity();
+
        return oldptr;
 }