X-Git-Url: https://git.liburcu.org/?a=blobdiff_plain;f=urcu.c;h=9542b264a6dbf53d36d2fb63e7578b4e7ff2b2f5;hb=9598a4814c854780e9ca9bb2cfff8d77442c3db6;hp=83d2fe4d6d9c367796d123fb05286f8305dfc332;hpb=9d335088c7c7eb6219e32ec9426d336f3a211a77;p=urcu.git

diff --git a/urcu.c b/urcu.c
index 83d2fe4..9542b26 100644
--- a/urcu.c
+++ b/urcu.c
@@ -19,17 +19,21 @@
 
 pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
 
-/* Global quiescent period parity */
-int urcu_qparity;
+/*
+ * 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;
 
-int __thread urcu_active_readers[2];
+long __thread urcu_active_readers;
 
 /* Thread IDs of registered readers */
 #define INIT_NUM_THREADS 4
 
 struct reader_data {
 	pthread_t tid;
-	int *urcu_active_readers;
+	long *urcu_active_readers;
 };
 
 #ifdef DEBUG_YIELD
@@ -65,13 +69,17 @@ void internal_urcu_unlock(void)
 /*
  * called with urcu_mutex held.
  */
-static int switch_next_urcu_qparity(void)
+static void switch_next_urcu_qparity(void)
 {
-	int old_parity = urcu_qparity;
-	urcu_qparity = 1 - old_parity;
-	return old_parity;
+	urcu_gp_ctr ^= RCU_GP_CTR_BIT;
 }
 
+#ifdef DEBUG_FULL_MB
+static void force_mb_all_threads(void)
+{
+	mb();
+}
+#else
 static void force_mb_all_threads(void)
 {
 	struct reader_data *index;
@@ -100,8 +108,9 @@ static void force_mb_all_threads(void)
 	mb();	/* read sig_done before ending the barrier */
 	debug_yield_write();
 }
+#endif
 
-void wait_for_quiescent_state(int parity)
+void wait_for_quiescent_state(void)
 {
 	struct reader_data *index;
 
@@ -113,82 +122,73 @@ void wait_for_quiescent_state(int parity)
 		/*
 		 * BUSY-LOOP.
 		 */
-		while (index->urcu_active_readers[parity] != 0)
+		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)
 {
-	int prev_parity;
-
-	/* 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();
-	prev_parity = 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(prev_parity);
-}
+	mb();
 
-void synchronize_rcu(void)
-{
-	debug_yield_write();
-	internal_urcu_lock();
-	debug_yield_write();
-	switch_qparity();
-	debug_yield_write();
-	switch_qparity();
-	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();
-}
 
-/*
- * Return old pointer, OK to free, no more reference exist.
- * Called under rcu_write_lock.
- */
-void *urcu_publish_content(void **ptr, void *new)
-{
-	void *oldptr;
+	/*
+	 * 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).
+	 */
+	mb();
 
+	switch_next_urcu_qparity();	/* 1 -> 0 */
 	debug_yield_write();
-	internal_urcu_lock();
-	debug_yield_write();
+
 	/*
-	 * We can publish the new pointer before we change the current qparity.
-	 * Readers seeing the new pointer while being in the previous qparity
-	 * window will make us wait until the end of the quiescent state before
-	 * we release the unrelated memory area. However, given we hold the
-	 * urcu_mutex, we are making sure that no further garbage collection can
-	 * occur until we release the mutex, therefore we guarantee that this
-	 * given reader will have completed its execution using the new pointer
-	 * when the next quiescent state window will be over.
+	 * 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).
 	 */
-	oldptr = *ptr;
-	debug_yield_write();
-	*ptr = new;
+	mb();
 
+	/*
+	 * Wait for previous parity to be empty of readers.
+	 */
+	wait_for_quiescent_state();	/* Wait readers in parity 1 */
 	debug_yield_write();
-	switch_qparity();
-	debug_yield_write();
-	switch_qparity();
-	debug_yield_write();
+
 	internal_urcu_unlock();
 	debug_yield_write();
 
-	return oldptr;
+	/* 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)
@@ -212,7 +212,7 @@ void urcu_add_reader(pthread_t id)
 	}
 	reader_data[num_readers].tid = id;
 	/* reference to the TLS of _this_ reader thread. */
-	reader_data[num_readers].urcu_active_readers = urcu_active_readers;
+	reader_data[num_readers].urcu_active_readers = &urcu_active_readers;
 	num_readers++;
 }
 
@@ -253,6 +253,7 @@ void urcu_unregister_thread(void)
 	internal_urcu_unlock();
 }
 
+#ifndef DEBUG_FULL_MB
 void sigurcu_handler(int signo, siginfo_t *siginfo, void *context)
 {
 	mb();
@@ -285,3 +286,4 @@ void __attribute__((destructor)) urcu_exit(void)
 	assert(act.sa_sigaction == sigurcu_handler);
 	free(reader_data);
 }
+#endif