X-Git-Url: https://git.liburcu.org/?a=blobdiff_plain;f=urcu.c;h=a78c02bdca6a71f9e7f66c76295fc8f1f33cdd37;hb=15302e2854ad9f1377ec81e331c1bec7a54a5621;hp=2d5c510aa6744418c5557d642b451e0afae415cd;hpb=c94886840694378921968b490ed1e09d1af3afb3;p=urcu.git

diff --git a/urcu.c b/urcu.c
index 2d5c510..a78c02b 100644
--- a/urcu.c
+++ b/urcu.c
@@ -43,6 +43,7 @@
 #include "urcu/tls-compat.h"
 
 #include "urcu-die.h"
+#include "urcu-wait.h"
 
 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
 #undef _LGPL_SOURCE
@@ -106,6 +107,12 @@ DEFINE_URCU_TLS(unsigned int, rcu_rand_yield);
 
 static CDS_LIST_HEAD(registry);
 
+/*
+ * Queue keeping threads awaiting to wait for a grace period. Contains
+ * struct gp_waiters_thread objects.
+ */
+static DEFINE_URCU_WAIT_QUEUE(gp_waiters);
+
 static void mutex_lock(pthread_mutex_t *mutex)
 {
 	int ret;
@@ -215,9 +222,10 @@ static void wait_gp(void)
 		      NULL, NULL, 0);
 }
 
-static void wait_for_readers(void)
+static void wait_for_readers(struct cds_list_head *input_readers,
+			struct cds_list_head *cur_snap_readers,
+			struct cds_list_head *qsreaders)
 {
-	CDS_LIST_HEAD(qsreaders);
 	int wait_loops = 0;
 	struct rcu_reader *index, *tmp;
 
@@ -234,13 +242,31 @@ static void wait_for_readers(void)
 			smp_mb_master(RCU_MB_GROUP);
 		}
 
-		cds_list_for_each_entry_safe(index, tmp, &registry, node) {
-			if (!rcu_gp_ongoing(&index->ctr))
-				cds_list_move(&index->node, &qsreaders);
+		cds_list_for_each_entry_safe(index, tmp, input_readers, node) {
+			switch (rcu_reader_state(&index->ctr)) {
+			case RCU_READER_ACTIVE_CURRENT:
+				if (cur_snap_readers) {
+					cds_list_move(&index->node,
+						cur_snap_readers);
+					break;
+				}
+				/* Fall-through */
+			case RCU_READER_INACTIVE:
+				cds_list_move(&index->node, qsreaders);
+				break;
+			case RCU_READER_ACTIVE_OLD:
+				/*
+				 * Old snapshot. Leaving node in
+				 * input_readers will make us busy-loop
+				 * until the snapshot becomes current or
+				 * the reader becomes inactive.
+				 */
+				break;
+			}
 		}
 
 #ifndef HAS_INCOHERENT_CACHES
-		if (cds_list_empty(&registry)) {
+		if (cds_list_empty(input_readers)) {
 			if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
 				/* Read reader_gp before write futex */
 				smp_mb_master(RCU_MB_GROUP);
@@ -259,7 +285,7 @@ static void wait_for_readers(void)
 		 * URCU_TLS(rcu_reader).ctr update to memory if we wait
 		 * for too long.
 		 */
-		if (cds_list_empty(&registry)) {
+		if (cds_list_empty(input_readers)) {
 			if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
 				/* Read reader_gp before write futex */
 				smp_mb_master(RCU_MB_GROUP);
@@ -281,14 +307,40 @@ static void wait_for_readers(void)
 		}
 #endif /* #else #ifndef HAS_INCOHERENT_CACHES */
 	}
-	/* put back the reader list in the registry */
-	cds_list_splice(&qsreaders, &registry);
 }
 
 void synchronize_rcu(void)
 {
+	CDS_LIST_HEAD(cur_snap_readers);
+	CDS_LIST_HEAD(qsreaders);
+	DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING);
+	struct urcu_waiters waiters;
+
+	/*
+	 * Add ourself to gp_waiters queue of threads awaiting to wait
+	 * for a grace period. Proceed to perform the grace period only
+	 * if we are the first thread added into the queue.
+	 * The implicit memory barrier before urcu_wait_add()
+	 * orders prior memory accesses of threads put into the wait
+	 * queue before their insertion into the wait queue.
+	 */
+	if (urcu_wait_add(&gp_waiters, &wait) != 0) {
+		/* Not first in queue: will be awakened by another thread. */
+		urcu_adaptative_busy_wait(&wait);
+		/* Order following memory accesses after grace period. */
+		cmm_smp_mb();
+		return;
+	}
+	/* We won't need to wake ourself up */
+	urcu_wait_set_state(&wait, URCU_WAIT_RUNNING);
+
 	mutex_lock(&rcu_gp_lock);
 
+	/*
+	 * Move all waiters into our local queue.
+	 */
+	urcu_move_waiters(&waiters, &gp_waiters);
+
 	if (cds_list_empty(&registry))
 		goto out;
 
@@ -301,7 +353,7 @@ void synchronize_rcu(void)
 	/*
 	 * Wait for readers to observe original parity or be quiescent.
 	 */
-	wait_for_readers();
+	wait_for_readers(&registry, &cur_snap_readers, &qsreaders);
 
 	/*
 	 * Must finish waiting for quiescent state for original parity before
@@ -341,7 +393,12 @@ void synchronize_rcu(void)
 	/*
 	 * Wait for readers to observe new parity or be quiescent.
 	 */
-	wait_for_readers();
+	wait_for_readers(&cur_snap_readers, NULL, &qsreaders);
+
+	/*
+	 * Put quiescent reader list back into registry.
+	 */
+	cds_list_splice(&qsreaders, &registry);
 
 	/* Finish waiting for reader threads before letting the old ptr being
 	 * freed. Must be done within rcu_gp_lock because it iterates on reader
@@ -349,6 +406,13 @@ void synchronize_rcu(void)
 	smp_mb_master(RCU_MB_GROUP);
 out:
 	mutex_unlock(&rcu_gp_lock);
+
+	/*
+	 * Wakeup waiters only after we have completed the grace period
+	 * and have ensured the memory barriers at the end of the grace
+	 * period have been issued.
+	 */
+	urcu_wake_all_waiters(&waiters);
 }
 
 /*
@@ -365,6 +429,11 @@ void rcu_read_unlock(void)
 	_rcu_read_unlock();
 }
 
+int rcu_read_ongoing(void)
+{
+	return _rcu_read_ongoing();
+}
+
 void rcu_register_thread(void)
 {
 	URCU_TLS(rcu_reader).tid = pthread_self();