X-Git-Url: https://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu-bp.c;h=61d42fa20188d6b12ab3a560cede576828a77099;hp=eda000539b19b01ce582fe098be1d1cc0f1a3b3f;hb=b0dd35e28adda68dc6a564cf770a5d422d62259f;hpb=6abb4bd53503c325dc94b0c0f60b44b9550b462f

diff --git a/urcu-bp.c b/urcu-bp.c
index eda0005..61d42fa 100644
--- a/urcu-bp.c
+++ b/urcu-bp.c
@@ -3,7 +3,7 @@
  *
  * Userspace RCU library, "bulletproof" version.
  *
- * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
+ * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
  * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
  *
  * This library is free software; you can redistribute it and/or
@@ -116,30 +116,37 @@ static void mutex_unlock(pthread_mutex_t *mutex)
 	}
 }
 
-/*
- * called with rcu_gp_lock held.
- */
-static void switch_next_rcu_qparity(void)
-{
-	STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE);
-}
-
-void wait_for_quiescent_state(void)
+void update_counter_and_wait(void)
 {
 	LIST_HEAD(qsreaders);
 	int wait_loops = 0;
 	struct rcu_reader *index, *tmp;
 
-	if (list_empty(&registry))
-		return;
+	/* Switch parity: 0 -> 1, 1 -> 0 */
+	STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE);
+
+	/*
+	 * Must commit qparity update to memory before waiting for other parity
+	 * 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.
+	 */
+
+	/*
+	 * Adding a smp_mb() which is _not_ formally required, but makes the
+	 * model easier to understand. It does not have a big performance impact
+	 * anyway, given this is the write-side.
+	 */
+	smp_mb();
+
 	/*
 	 * Wait for each thread rcu_reader.ctr count to become 0.
 	 */
 	for (;;) {
 		wait_loops++;
-		list_for_each_entry_safe(index, tmp, &registry, head) {
+		list_for_each_entry_safe(index, tmp, &registry, node) {
 			if (!rcu_old_gp_ongoing(&index->ctr))
-				list_move(&index->head, &qsreaders);
+				list_move(&index->node, &qsreaders);
 		}
 
 		if (list_empty(&registry)) {
@@ -167,44 +174,21 @@ void synchronize_rcu(void)
 
 	mutex_lock(&rcu_gp_lock);
 
-	/* Remove old registry elements */
-	rcu_gc_registry();
+	if (list_empty(&registry))
+		goto out;
 
 	/* All threads should read qparity before accessing data structure
-	 * where new ptr points to. Must be done within rcu_gp_lock because it
-	 * iterates on reader threads.*/
+	 * where new ptr points to. */
 	/* Write new ptr before changing the qparity */
 	smp_mb();
 
-	switch_next_rcu_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.
-	 */
-
-	/*
-	 * Adding a smp_mb() which is _not_ formally required, but makes the
-	 * model easier to understand. It does not have a big performance impact
-	 * anyway, given this is the write-side.
-	 */
-	smp_mb();
+	/* Remove old registry elements */
+	rcu_gc_registry();
 
 	/*
 	 * 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.
-	 */
+	update_counter_and_wait();	/* 0 -> 1, wait readers in parity 0 */
 
 	/*
 	 * Adding a smp_mb() which is _not_ formally required, but makes the
@@ -213,33 +197,17 @@ void synchronize_rcu(void)
 	 */
 	smp_mb();
 
-	switch_next_rcu_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.
-	 */
-
-	/*
-	 * Adding a smp_mb() which is _not_ formally required, but makes the
-	 * model easier to understand. It does not have a big performance impact
-	 * anyway, given this is the write-side.
+	 * Wait for previous parity to be empty of readers.
 	 */
-	smp_mb();
+	update_counter_and_wait();	/* 1 -> 0, wait readers in parity 1 */
 
 	/*
-	 * Wait for previous parity to be empty of readers.
+	 * Finish waiting for reader threads before letting the old ptr being
+	 * freed.
 	 */
-	wait_for_quiescent_state();	/* Wait readers in parity 1 */
-
-	/* Finish waiting for reader threads before letting the old ptr being
-	 * freed. Must be done within rcu_gp_lock because it iterates on reader
-	 * threads. */
 	smp_mb();
-
+out:
 	mutex_unlock(&rcu_gp_lock);
 	ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 	assert(!ret);
@@ -311,7 +279,7 @@ static void add_thread(void)
 	/* Add to registry */
 	rcu_reader_reg->tid = pthread_self();
 	assert(rcu_reader_reg->ctr == 0);
-	list_add(&rcu_reader_reg->head, &registry);
+	list_add(&rcu_reader_reg->node, &registry);
 	rcu_reader = rcu_reader_reg;
 }
 
@@ -331,7 +299,8 @@ static void rcu_gc_registry(void)
 		ret = pthread_kill(tid, 0);
 		assert(ret != EINVAL);
 		if (ret == ESRCH) {
-			list_del(&rcu_reader_reg->head);
+			list_del(&rcu_reader_reg->node);
+			rcu_reader_reg->ctr = 0;
 			rcu_reader_reg->alloc = 0;
 			registry_arena.used -= sizeof(struct rcu_reader);
 		}