X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu-qsbr.c;h=f681c05bf0c05d96860e06cbb8771b11c9e3e829;hp=c0f055441930ab8718cd4d4347325bd6671dc2fc;hb=b55487c706982c8190e42545f7f74dfadad59548;hpb=d1238495fdaf1c85447690231bf5d1838b83bf88

diff --git a/urcu-qsbr.c b/urcu-qsbr.c
index c0f0554..f681c05 100644
--- a/urcu-qsbr.c
+++ b/urcu-qsbr.c
@@ -32,29 +32,30 @@
 #include <errno.h>
 #include <poll.h>
 
+#define BUILD_QSBR_LIB
 #include "urcu-qsbr-static.h"
 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
 #include "urcu-qsbr.h"
 
-pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
+static pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
 
 /*
  * Global grace period counter.
  */
-long urcu_gp_ctr = 0;
+unsigned long urcu_gp_ctr = RCU_GP_ONLINE;
 
 /*
  * Written to only by each individual reader. Read by both the reader and the
  * writers.
  */
-long __thread rcu_reader_qs_gp;
+unsigned long __thread rcu_reader_qs_gp;
 
 /* Thread IDs of registered readers */
 #define INIT_NUM_THREADS 4
 
 struct reader_registry {
 	pthread_t tid;
-	long *rcu_reader_qs_gp;
+	unsigned long *rcu_reader_qs_gp;
 };
 
 #ifdef DEBUG_YIELD
@@ -98,25 +99,10 @@ static void internal_urcu_unlock(void)
 	}
 }
 
-#ifdef HAS_INCOHERENT_CACHES
-static void force_mb_single_thread(struct reader_registry *index)
-{
-	smp_mb();
-}
-#endif /* #ifdef HAS_INCOHERENT_CACHES */
-
-static void force_mb_all_threads(void)
-{
-	smp_mb();
-}
-
 static void wait_for_quiescent_state(void)
 {
 	struct reader_registry *index;
 
-        if (rcu_reader_qs_gp & 1)
-            rcu_reader_qs_gp = urcu_gp_ctr + 1;
-
 	if (!registry)
 		return;
 	/*
@@ -124,37 +110,125 @@ static void wait_for_quiescent_state(void)
 	 */
 	for (index = registry; index < registry + num_readers; index++) {
 #ifndef HAS_INCOHERENT_CACHES
-		while (rcu_gp_ongoing(index->rcu_reader_qs_gp) &&
-		       (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0))
+		while (rcu_gp_ongoing(index->rcu_reader_qs_gp))
 			cpu_relax();
 #else /* #ifndef HAS_INCOHERENT_CACHES */
-		int wait_loops = 0;
-		/*
-		 * BUSY-LOOP. Force the reader thread to commit its
-		 * rcu_reader_qs_gp update to memory if we wait for too long.
-		 */
-		while (rcu_gp_ongoing(index->rcu_reader_qs_gp) &&
-		       (*index->rcu_reader_qs_gp - urcu_gp_ctr < 0)) {
-			if (wait_loops++ == KICK_READER_LOOPS) {
-				force_mb_single_thread(index);
-				wait_loops = 0;
-			} else {
-				cpu_relax();
-			}
-		}
+		while (rcu_gp_ongoing(index->rcu_reader_qs_gp))
+			smp_mb();
 #endif /* #else #ifndef HAS_INCOHERENT_CACHES */
 	}
 }
 
+/*
+ * Using a two-subphases algorithm for architectures with smaller than 64-bit
+ * long-size to ensure we do not encounter an overflow bug.
+ */
+
+#if (BITS_PER_LONG < 64)
+/*
+ * called with urcu_mutex held.
+ */
+static void switch_next_urcu_qparity(void)
+{
+	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR);
+}
+
 void synchronize_rcu(void)
 {
+	unsigned long was_online;
+
+	was_online = rcu_reader_qs_gp;
+
+	/* All threads should read qparity before accessing data structure
+	 * where new ptr points to.
+	 */
+	/* Write new ptr before changing the qparity */
+	smp_mb();
+
+	/*
+	 * Mark the writer thread offline to make sure we don't wait for
+	 * our own quiescent state. This allows using synchronize_rcu() in
+	 * threads registered as readers.
+	 */
+	if (was_online)
+		STORE_SHARED(rcu_reader_qs_gp, 0);
+
 	internal_urcu_lock();
-	force_mb_all_threads();
-	urcu_gp_ctr += 2;
+
+	switch_next_urcu_qparity();	/* 0 -> 1 */
+
+	/*
+	 * 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).
+	 * Ensured by STORE_SHARED and LOAD_SHARED.
+	 */
+
+	/*
+	 * Wait for previous parity to be empty of readers.
+	 */
+	wait_for_quiescent_state();	/* Wait readers in parity 0 */
+
+	/*
+	 * 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).
+	 * Ensured by STORE_SHARED and LOAD_SHARED.
+	 */
+
+	switch_next_urcu_qparity();	/* 1 -> 0 */
+
+	/*
+	 * 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).
+	 * Ensured by STORE_SHARED and LOAD_SHARED.
+	 */
+
+	/*
+	 * Wait for previous parity to be empty of readers.
+	 */
+	wait_for_quiescent_state();	/* Wait readers in parity 1 */
+
+	internal_urcu_unlock();
+
+	/*
+	 * Finish waiting for reader threads before letting the old ptr being
+	 * freed.
+	 */
+	if (was_online)
+		_STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr));
+	smp_mb();
+}
+#else /* !(BITS_PER_LONG < 64) */
+void synchronize_rcu(void)
+{
+	unsigned long was_online;
+
+	was_online = rcu_reader_qs_gp;
+
+	/*
+	 * Mark the writer thread offline to make sure we don't wait for
+	 * our own quiescent state. This allows using synchronize_rcu() in
+	 * threads registered as readers.
+	 */
+	smp_mb();
+	if (was_online)
+		STORE_SHARED(rcu_reader_qs_gp, 0);
+
+	internal_urcu_lock();
+	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr + RCU_GP_CTR);
 	wait_for_quiescent_state();
-	force_mb_all_threads();
 	internal_urcu_unlock();
+
+	if (was_online)
+		_STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr));
+	smp_mb();
 }
+#endif  /* !(BITS_PER_LONG < 64) */
 
 /*
  * library wrappers to be used by non-LGPL compatible source code.