X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu-qsbr.c;h=dac664935d7b898bd3dcce494845c7471c09749d;hp=5c6eaa014721267da7de5f85fff22835d41a80b2;hb=bc6c15bba37d0e6192c006c4d9815201b36d1988;hpb=8fd3b21900597654e15eb8cda2e97606a4b1d9bf

diff --git a/urcu-qsbr.c b/urcu-qsbr.c
index 5c6eaa0..dac6649 100644
--- a/urcu-qsbr.c
+++ b/urcu-qsbr.c
@@ -39,6 +39,8 @@
 
 static pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
 
+int gp_futex;
+
 /*
  * Global grace period counter.
  */
@@ -99,6 +101,27 @@ static void internal_urcu_unlock(void)
 	}
 }
 
+/*
+ * synchronize_rcu() waiting. Single thread.
+ */
+static void wait_gp(struct reader_registry *index)
+{
+	atomic_dec(&gp_futex);
+	smp_mb(); /* Write futex before read reader_gp */
+	if (!rcu_gp_ongoing(index->rcu_reader_qs_gp)) {
+		/* Read reader_gp before write futex */
+		smp_mb();
+		/* Callbacks are queued, don't wait. */
+		atomic_set(&gp_futex, 0);
+	} else {
+		/* Read reader_gp before read futex */
+		smp_rmb();
+		if (atomic_read(&gp_futex) == -1)
+			futex(&gp_futex, FUTEX_WAIT, -1,
+			      NULL, NULL, 0);
+	}
+}
+
 static void wait_for_quiescent_state(void)
 {
 	struct reader_registry *index;
@@ -109,13 +132,19 @@ static void wait_for_quiescent_state(void)
 	 * Wait for each thread rcu_reader_qs_gp count to become 0.
 	 */
 	for (index = registry; index < registry + num_readers; index++) {
+		int wait_loops = 0;
+
+		while (rcu_gp_ongoing(index->rcu_reader_qs_gp)) {
+			if (wait_loops++ == RCU_QS_ACTIVE_ATTEMPTS) {
+				wait_gp(index);
+			} else {
 #ifndef HAS_INCOHERENT_CACHES
-		while (rcu_gp_ongoing(index->rcu_reader_qs_gp))
-			cpu_relax();
+				cpu_relax();
 #else /* #ifndef HAS_INCOHERENT_CACHES */
-		while (rcu_gp_ongoing(index->rcu_reader_qs_gp))
-			smp_mb();
+				smp_mb();
 #endif /* #else #ifndef HAS_INCOHERENT_CACHES */
+			}
+		}
 	}
 }