urcu-mb/signal/membarrier: batch concurrent synchronize_rcu()

[urcu.git] / urcu.c

diff --git a/urcu.c b/urcu.c
index e6ff0f349e9e4fef17d6d366b5e7197acb841b84..15def09adb7e7feeeaba49f2d1d2a1c33a90bf59 100644 (file)
--- 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;
@@ -306,9 +313,34 @@ 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;
 
@@ -374,6 +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);
 }
 
 /*