Wait-free stack: rcu-less implementation
authorMathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Wed, 18 Aug 2010 14:55:14 +0000 (10:55 -0400)
committerMathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Wed, 18 Aug 2010 14:55:14 +0000 (10:55 -0400)
Don't have to hold a rcu read lock anymore. pop side is blocking and holds a
mutex.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Makefile.am
tests/test_urcu_wfs.c
urcu/rcuwfstack.h [deleted file]
urcu/wfstack.h [new file with mode: 0644]

index 88755387de1affda6903beff12c29dfbefa7e7d3..88214ab4ff1254fc8a90faac0294b64467718f98 100644 (file)
@@ -7,7 +7,8 @@ SUBDIRS = . tests
 include_HEADERS = urcu.h $(top_srcdir)/urcu-*.h
 nobase_dist_include_HEADERS = urcu/compiler.h urcu/hlist.h urcu/list.h \
                urcu/rculist.h urcu/rcuhlist.h urcu/system.h urcu/urcu-futex.h \
-               urcu/uatomic_generic.h urcu/arch_generic.h
+               urcu/uatomic_generic.h urcu/arch_generic.h urcu/wfstack.h \
+               urcu/wfqueue.h urcu/rculfstack.h urcu/rculfqueue.h
 nobase_nodist_include_HEADERS = urcu/arch.h urcu/uatomic_arch.h urcu/config.h
 
 EXTRA_DIST = $(top_srcdir)/urcu/arch_*.h $(top_srcdir)/urcu/uatomic_arch_*.h \
index 73655c1dcec7c6ffbb8b23f42d2acb544eb54ff0..f50b1400ffdd95d847d19ef8e256677982ffd734 100644 (file)
@@ -62,8 +62,7 @@ static inline pid_t gettid(void)
 #define _LGPL_SOURCE
 #endif
 #include <urcu.h>
-#include <urcu/rcuwfstack.h>
-#include <urcu-defer.h>
+#include <urcu/wfstack.h>
 
 static volatile int test_go, test_stop;
 
@@ -154,7 +153,7 @@ static unsigned long long __thread nr_successful_enqueues;
 static unsigned int nr_enqueuers;
 static unsigned int nr_dequeuers;
 
-static struct rcu_wfs_stack s;
+static struct wfs_stack s;
 
 void *thr_enqueuer(void *_count)
 {
@@ -165,19 +164,17 @@ void *thr_enqueuer(void *_count)
 
        set_affinity();
 
-       rcu_register_thread();
-
        while (!test_go)
        {
        }
        smp_mb();
 
        for (;;) {
-               struct rcu_wfs_node *node = malloc(sizeof(*node));
+               struct wfs_node *node = malloc(sizeof(*node));
                if (!node)
                        goto fail;
-               rcu_wfs_node_init(node);
-               rcu_wfs_push(&s, node);
+               wfs_node_init(node);
+               wfs_push(&s, node);
                nr_successful_enqueues++;
 
                if (unlikely(wdelay))
@@ -188,8 +185,6 @@ fail:
                        break;
        }
 
-       rcu_unregister_thread();
-
        count[0] = nr_enqueues;
        count[1] = nr_successful_enqueues;
        printf_verbose("enqueuer thread_end, thread id : %lx, tid %lu, "
@@ -209,19 +204,16 @@ void *thr_dequeuer(void *_count)
 
        set_affinity();
 
-       rcu_defer_register_thread();
-       rcu_register_thread();
-
        while (!test_go)
        {
        }
        smp_mb();
 
        for (;;) {
-               struct rcu_wfs_node *node = rcu_wfs_pop_blocking(&s);
+               struct wfs_node *node = wfs_pop_blocking(&s);
 
                if (node) {
-                       defer_rcu(free, node);
+                       free(node);
                        nr_successful_dequeues++;
                }
 
@@ -232,9 +224,6 @@ void *thr_dequeuer(void *_count)
                        loop_sleep(rduration);
        }
 
-       rcu_unregister_thread();
-       rcu_defer_unregister_thread();
-
        printf_verbose("dequeuer thread_end, thread id : %lx, tid %lu, "
                       "dequeues %llu, successful_dequeues %llu\n",
                       pthread_self(), (unsigned long)gettid(), nr_dequeues,
@@ -244,12 +233,12 @@ void *thr_dequeuer(void *_count)
        return ((void*)2);
 }
 
-void test_end(struct rcu_wfs_stack *s, unsigned long long *nr_dequeues)
+void test_end(struct wfs_stack *s, unsigned long long *nr_dequeues)
 {
-       struct rcu_wfs_node *node;
+       struct wfs_node *node;
 
        do {
-               node = rcu_wfs_pop_blocking(s);
+               node = wfs_pop_blocking(s);
                if (node) {
                        free(node);
                        (*nr_dequeues)++;
@@ -348,7 +337,7 @@ int main(int argc, char **argv)
        tid_dequeuer = malloc(sizeof(*tid_dequeuer) * nr_dequeuers);
        count_enqueuer = malloc(2 * sizeof(*count_enqueuer) * nr_enqueuers);
        count_dequeuer = malloc(2 * sizeof(*count_dequeuer) * nr_dequeuers);
-       rcu_wfs_init(&s);
+       wfs_init(&s);
 
        next_aff = 0;
 
diff --git a/urcu/rcuwfstack.h b/urcu/rcuwfstack.h
deleted file mode 100644 (file)
index 71ecce8..0000000
+++ /dev/null
@@ -1,133 +0,0 @@
-#ifndef _URCU_RCUWFSTACK_H
-#define _URCU_RCUWFSTACK_H
-
-/*
- * rcuwfstack.h
- *
- * Userspace RCU library - RCU Stack with Wait-Free push, Blocking pop.
- *
- * Copyright 2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
- *
- * This library is free software; you can redistribute it and/or
- * modify it under the terms of the GNU Lesser General Public
- * License as published by the Free Software Foundation; either
- * version 2.1 of the License, or (at your option) any later version.
- *
- * This library is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
- * Lesser General Public License for more details.
- *
- * You should have received a copy of the GNU Lesser General Public
- * License along with this library; if not, write to the Free Software
- * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
- */
-
-#include <assert.h>
-
-#ifdef __cplusplus
-extern "C" {
-#endif
-
-#if (!defined(_GNU_SOURCE) && !defined(_LGPL_SOURCE))
-#error "Dynamic loader LGPL wrappers not implemented yet"
-#endif
-
-#define RCU_WF_STACK_END               ((void *)0x1UL)
-#define RCU_WFS_ADAPT_ATTEMPTS         10      /* Retry if being set */
-#define RCU_WFS_WAIT                   10      /* Wait 10 ms if being set */
-
-extern int rcu_wfs_futex;
-
-struct rcu_wfs_node {
-       struct rcu_wfs_node *next;
-};
-
-struct rcu_wfs_stack {
-       struct rcu_wfs_node *head;
-};
-
-void rcu_wfs_node_init(struct rcu_wfs_node *node)
-{
-       node->next = NULL;
-}
-
-void rcu_wfs_init(struct rcu_wfs_stack *s)
-{
-       s->head = RCU_WF_STACK_END;
-}
-
-void rcu_wfs_push(struct rcu_wfs_stack *s, struct rcu_wfs_node *node)
-{
-       struct rcu_wfs_node *old_head;
-
-       assert(node->next == NULL);
-       /*
-        * uatomic_xchg() implicit memory barrier orders earlier stores to node
-        * (setting it to NULL) before publication.
-        */
-       old_head = uatomic_xchg(&s->head, node);
-       /*
-        * At this point, dequeuers see a NULL node->next, they should busy-wait
-        * until node->next is set to old_head.
-        */
-       STORE_SHARED(node->next, old_head);
-}
-
-/*
- * The caller must wait for a grace period before:
- * - freeing the returned node.
- * - modifying the ->next pointer of the returned node. (be careful with unions)
- * - passing the returned node back to push() on the same stack they got it
- *   from.
- *
- * Returns NULL if stack is empty.
- *
- * cmpxchg is protected from ABA races by holding a RCU read lock between
- * s->head read and cmpxchg modifying s->head and requiring that dequeuers wait
- * for a grace period before freeing the returned node.
- */
-struct rcu_wfs_node *
-rcu_wfs_pop_blocking(struct rcu_wfs_stack *s)
-{
-       int attempt = 0;
-
-       for (;;) {
-               struct rcu_wfs_node *head;
-
-               rcu_read_lock();
-               head = rcu_dereference(s->head);
-               if (head != RCU_WF_STACK_END) {
-                       struct rcu_wfs_node *next = rcu_dereference(head->next);
-
-                       /* Retry while head is being set by push(). */
-                       if (!next) {
-                               rcu_read_unlock();
-                               if (++attempt >= RCU_WFS_ADAPT_ATTEMPTS) {
-                                       /* Sleep for 10ms */
-                                       poll(NULL, 0, RCU_WFS_WAIT);
-                                       attempt = 0;
-                               }
-                               continue;
-                       }
-                       if (uatomic_cmpxchg(&s->head, head, next) == head) {
-                               rcu_read_unlock();
-                               return head;
-                       } else {
-                               /* Concurrent modification. Retry. */
-                               rcu_read_unlock();
-                               continue;
-                       }
-               } else {
-                       /* Empty stack */
-                       rcu_read_unlock();
-                       return NULL;
-               }
-       }
-}
-
-#ifdef __cplusplus
-}
-#endif
-
-#endif /* _URCU_RCUWFSTACK_H */
diff --git a/urcu/wfstack.h b/urcu/wfstack.h
new file mode 100644 (file)
index 0000000..b3ee2e7
--- /dev/null
@@ -0,0 +1,129 @@
+#ifndef _URCU_WFSTACK_H
+#define _URCU_WFSTACK_H
+
+/*
+ * rcuwfstack.h
+ *
+ * Userspace RCU library - Stack with Wait-Free push, Blocking pop.
+ *
+ * Copyright 2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <pthread.h>
+#include <assert.h>
+#include <urcu/compiler.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#if (!defined(_GNU_SOURCE) && !defined(_LGPL_SOURCE))
+#error "Dynamic loader LGPL wrappers not implemented yet"
+#endif
+
+#define WF_STACK_END                   ((void *)0x1UL)
+#define WFS_ADAPT_ATTEMPTS             10      /* Retry if being set */
+#define WFS_WAIT                       10      /* Wait 10 ms if being set */
+
+struct wfs_node {
+       struct wfs_node *next;
+};
+
+struct wfs_stack {
+       struct wfs_node *head;
+       pthread_mutex_t lock;
+};
+
+void wfs_node_init(struct wfs_node *node)
+{
+       node->next = NULL;
+}
+
+void wfs_init(struct wfs_stack *s)
+{
+       int ret;
+
+       s->head = WF_STACK_END;
+       ret = pthread_mutex_init(&s->lock, NULL);
+       assert(!ret);
+}
+
+void wfs_push(struct wfs_stack *s, struct wfs_node *node)
+{
+       struct wfs_node *old_head;
+
+       assert(node->next == NULL);
+       /*
+        * uatomic_xchg() implicit memory barrier orders earlier stores to node
+        * (setting it to NULL) before publication.
+        */
+       old_head = uatomic_xchg(&s->head, node);
+       /*
+        * At this point, dequeuers see a NULL node->next, they should busy-wait
+        * until node->next is set to old_head.
+        */
+       STORE_SHARED(node->next, old_head);
+}
+
+/*
+ * Returns NULL if stack is empty.
+ */
+struct wfs_node *
+__wfs_pop_blocking(struct wfs_stack *s)
+{
+       struct wfs_node *head, *next;
+       int attempt = 0;
+
+retry:
+       head = LOAD_SHARED(s->head);
+       if (head == WF_STACK_END)
+               return NULL;
+       /*
+        * Adaptative busy-looping waiting for push to complete.
+        */
+       while ((next = LOAD_SHARED(head->next)) == NULL) {
+               if (++attempt >= WFS_ADAPT_ATTEMPTS) {
+                       poll(NULL, 0, WFS_WAIT);        /* Wait for 10ms */
+                       attempt = 0;
+               } else
+                       cpu_relax();
+       }
+       if (uatomic_cmpxchg(&s->head, head, next) == head)
+               return head;
+       else
+               goto retry;             /* Concurrent modification. Retry. */
+}
+
+struct wfs_node *
+wfs_pop_blocking(struct wfs_stack *s)
+{
+       struct wfs_node *retnode;
+       int ret;
+
+       ret = pthread_mutex_lock(&s->lock);
+       assert(!ret);
+       retnode = __wfs_pop_blocking(s);
+       ret = pthread_mutex_unlock(&s->lock);
+       assert(!ret);
+       return retnode;
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _URCU_WFSTACK_H */
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