X-Git-Url: http://git.liburcu.org/?a=blobdiff_plain;f=urcu%2Fwfstack.h;fp=urcu%2Fwfstack.h;h=b3ee2e7c4585e6e2f735a81ce82b67db3f84a5e2;hb=cb3f3d6bce4faeb41e4109e12fa722f73a6f6c13;hp=0000000000000000000000000000000000000000;hpb=4afee0a75aa60a2640afc9ebccc417c3179b276e;p=userspace-rcu.git

diff --git a/urcu/wfstack.h b/urcu/wfstack.h
new file mode 100644
index 0000000..b3ee2e7
--- /dev/null
+++ b/urcu/wfstack.h
@@ -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 */