Add barriers

[urcu.git] / urcu.c

diff --git a/urcu.c b/urcu.c
index 018e09b8601b041621fc6f72afdaeb57839e895c..0e42207e2bcd59d82127dc308def83b85c424798 100644 (file)
--- a/urcu.c
+++ b/urcu.c
@@ -77,11 +77,32 @@ static void switch_next_urcu_qparity(void)
 }
 
 #ifdef DEBUG_FULL_MB
+static void force_mb_single_thread(pthread_t tid)
+{
+       smp_mb();
+}
+
 static void force_mb_all_threads(void)
 {
        smp_mb();
 }
 #else
+
+static void force_mb_single_thread(pthread_t tid)
+{
+       assert(reader_data);
+       sig_done = 0;
+       smp_mb();       /* write sig_done before sending the signals */
+       pthread_kill(tid, SIGURCU);
+       /*
+        * Wait for sighandler (and thus mb()) to execute on every thread.
+        * BUSY-LOOP.
+        */
+       while (sig_done < 1)
+               smp_rmb();      /* ensure we re-read sig-done */
+       smp_mb();       /* read sig_done before ending the barrier */
+}
+
 static void force_mb_all_threads(void)
 {
        struct reader_data *index;
@@ -100,7 +121,7 @@ static void force_mb_all_threads(void)
         * BUSY-LOOP.
         */
        while (sig_done < num_readers)
-               barrier();
+               smp_rmb();      /* ensure we re-read sig-done */
        smp_mb();       /* read sig_done before ending the barrier */
 }
 #endif
@@ -111,14 +132,21 @@ void wait_for_quiescent_state(void)
 
        if (!reader_data)
                return;
-       /* Wait for each thread urcu_active_readers count to become 0.
+       /*
+        * Wait for each thread urcu_active_readers count to become 0.
         */
        for (index = reader_data; index < reader_data + num_readers; index++) {
+               int wait_loops = 0;
                /*
-                * BUSY-LOOP.
+                * BUSY-LOOP. Force the reader thread to commit its
+                * urcu_active_readers update to memory if we wait for too long.
                 */
-               while (rcu_old_gp_ongoing(index->urcu_active_readers))
-                       barrier();
+               while (rcu_old_gp_ongoing(index->urcu_active_readers)) {
+                       if (wait_loops++ == KICK_READER_LOOPS) {
+                               force_mb_single_thread(index->tid);
+                               wait_loops = 0;
+                       }
+               }
        }
 }
 
@@ -243,6 +271,11 @@ void urcu_unregister_thread(void)
 #ifndef DEBUG_FULL_MB
 void sigurcu_handler(int signo, siginfo_t *siginfo, void *context)
 {
+       /*
+        * Executing this smp_mb() is the only purpose of this signal handler.
+        * It punctually promotes barrier() into smp_mb() on every thread it is
+        * executed on.
+        */
        smp_mb();
        atomic_inc(&sig_done);
 }