X-Git-Url: http://git.liburcu.org/?a=blobdiff_plain;f=urcu.c;h=162ce00fa2d4c5516ef6093722d4dfc7b17cda23;hb=b715b99eb0d52e0744bfea46c62849f260a5ec58;hp=53c7f37677f762280b2a6337a6820bdf22c55faf;hpb=6e8b8429a09800f5a50f0410f5ec4cd95b46974b;p=userspace-rcu.git

diff --git a/urcu.c b/urcu.c
index 53c7f37..162ce00 100644
--- a/urcu.c
+++ b/urcu.c
@@ -19,8 +19,12 @@
 
 pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
 
-/* Global grace period counter */
-long urcu_gp_ctr;
+/*
+ * Global grace period counter.
+ * Contains the current RCU_GP_CTR_BIT.
+ * Also has a RCU_GP_CTR_BIT of 1, to accelerate the reader fast path.
+ */
+long urcu_gp_ctr = RCU_GP_COUNT;
 
 long __thread urcu_active_readers;
 
@@ -29,7 +33,7 @@ long __thread urcu_active_readers;
 
 struct reader_data {
 	pthread_t tid;
-	int *urcu_active_readers;
+	long *urcu_active_readers;
 };
 
 #ifdef DEBUG_YIELD
@@ -39,7 +43,9 @@ unsigned int __thread rand_yield;
 
 static struct reader_data *reader_data;
 static int num_readers, alloc_readers;
+#ifndef DEBUG_FULL_MB
 static int sig_done;
+#endif
 
 void internal_urcu_lock(void)
 {
@@ -70,11 +76,17 @@ static void switch_next_urcu_qparity(void)
 	urcu_gp_ctr ^= RCU_GP_CTR_BIT;
 }
 
+#ifdef DEBUG_FULL_MB
+static void force_mb_all_threads(void)
+{
+	smp_mb();
+}
+#else
 static void force_mb_all_threads(void)
 {
 	struct reader_data *index;
 	/*
-	 * Ask for each threads to execute a mb() so we can consider the
+	 * Ask for each threads to execute a smp_mb() so we can consider the
 	 * compiler barriers around rcu read lock as real memory barriers.
 	 */
 	if (!reader_data)
@@ -82,7 +94,7 @@ static void force_mb_all_threads(void)
 	debug_yield_write();
 	sig_done = 0;
 	debug_yield_write();
-	mb();	/* write sig_done before sending the signals */
+	smp_mb();	/* write sig_done before sending the signals */
 	debug_yield_write();
 	for (index = reader_data; index < reader_data + num_readers; index++) {
 		pthread_kill(index->tid, SIGURCU);
@@ -95,9 +107,10 @@ static void force_mb_all_threads(void)
 	while (sig_done < num_readers)
 		barrier();
 	debug_yield_write();
-	mb();	/* read sig_done before ending the barrier */
+	smp_mb();	/* read sig_done before ending the barrier */
 	debug_yield_write();
 }
+#endif
 
 void wait_for_quiescent_state(void)
 {
@@ -114,41 +127,70 @@ void wait_for_quiescent_state(void)
 		while (rcu_old_gp_ongoing(index->urcu_active_readers))
 			barrier();
 	}
-	/*
-	 * Locally : read *index->urcu_active_readers before freeing old
-	 * pointer.
-	 * Remote (reader threads) : Order urcu_qparity update and other
-	 * thread's quiescent state counter read.
-	 */
-	force_mb_all_threads();
 }
 
-static void switch_qparity(void)
+void synchronize_rcu(void)
 {
-	/* All threads should read qparity before accessing data structure. */
-	/* Write ptr before changing the qparity */
+	/* All threads should read qparity before accessing data structure
+	 * where new ptr points to. */
+	/* Write new ptr before changing the qparity */
 	force_mb_all_threads();
 	debug_yield_write();
-	switch_next_urcu_qparity();
+
+	internal_urcu_lock();
+	debug_yield_write();
+
+	switch_next_urcu_qparity();	/* 0 -> 1 */
 	debug_yield_write();
 
 	/*
-	 * Wait for previous parity to be empty of readers.
+	 * 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).
 	 */
-	wait_for_quiescent_state();
-}
+	smp_mb();
 
-void synchronize_rcu(void)
-{
-	debug_yield_write();
-	internal_urcu_lock();
+	/*
+	 * Wait for previous parity to be empty of readers.
+	 */
+	wait_for_quiescent_state();	/* Wait readers in parity 0 */
 	debug_yield_write();
-	switch_qparity();
+
+	/*
+	 * Must finish waiting for quiescent state for parity 0 before
+	 * committing qparity update to memory. Failure to do so could result in
+	 * the writer waiting forever while new readers are always accessing
+	 * data (no progress).
+	 */
+	smp_mb();
+
+	switch_next_urcu_qparity();	/* 1 -> 0 */
 	debug_yield_write();
-	switch_qparity();
+
+	/*
+	 * 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).
+	 */
+	smp_mb();
+
+	/*
+	 * Wait for previous parity to be empty of readers.
+	 */
+	wait_for_quiescent_state();	/* Wait readers in parity 1 */
 	debug_yield_write();
+
 	internal_urcu_unlock();
 	debug_yield_write();
+
+	/* All threads should finish using the data referred to by old ptr
+	 * before decrementing their urcu_active_readers count */
+	/* Finish waiting for reader threads before letting the old ptr being
+	 * freed. */
+	force_mb_all_threads();
+	debug_yield_write();
 }
 
 void urcu_add_reader(pthread_t id)
@@ -213,9 +255,10 @@ void urcu_unregister_thread(void)
 	internal_urcu_unlock();
 }
 
+#ifndef DEBUG_FULL_MB
 void sigurcu_handler(int signo, siginfo_t *siginfo, void *context)
 {
-	mb();
+	smp_mb();
 	atomic_inc(&sig_done);
 }
 
@@ -245,3 +288,4 @@ void __attribute__((destructor)) urcu_exit(void)
 	assert(act.sa_sigaction == sigurcu_handler);
 	free(reader_data);
 }
+#endif