Cleanup: Re-organise source dir

[userspace-rcu.git] / include / urcu / static / wfqueue.h

diff --git a/include/urcu/static/wfqueue.h b/include/urcu/static/wfqueue.h
new file mode 100644 (file)
index 0000000..df9f62f
--- /dev/null
+++ b/include/urcu/static/wfqueue.h
@@ -0,0 +1,171 @@
+#ifndef _URCU_WFQUEUE_STATIC_H
+#define _URCU_WFQUEUE_STATIC_H
+
+/*
+ * wfqueue-static.h
+ *
+ * Userspace RCU library - Queue with Wait-Free Enqueue/Blocking Dequeue
+ *
+ * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See wfqueue.h for linking
+ * dynamically with the userspace rcu library.
+ *
+ * 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 <poll.h>
+#include <urcu/compiler.h>
+#include <urcu/uatomic.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/*
+ * Queue with wait-free enqueue/blocking dequeue.
+ * This implementation adds a dummy head node when the queue is empty to ensure
+ * we can always update the queue locklessly.
+ *
+ * Inspired from half-wait-free/half-blocking queue implementation done by
+ * Paul E. McKenney.
+ */
+
+#define WFQ_ADAPT_ATTEMPTS             10      /* Retry if being set */
+#define WFQ_WAIT                       10      /* Wait 10 ms if being set */
+
+static inline void _cds_wfq_node_init(struct cds_wfq_node *node)
+{
+       node->next = NULL;
+}
+
+static inline void _cds_wfq_init(struct cds_wfq_queue *q)
+{
+       int ret;
+
+       _cds_wfq_node_init(&q->dummy);
+       /* Set queue head and tail */
+       q->head = &q->dummy;
+       q->tail = &q->dummy.next;
+       ret = pthread_mutex_init(&q->lock, NULL);
+       assert(!ret);
+}
+
+static inline void _cds_wfq_destroy(struct cds_wfq_queue *q)
+{
+       int ret = pthread_mutex_destroy(&q->lock);
+       assert(!ret);
+}
+
+static inline void _cds_wfq_enqueue(struct cds_wfq_queue *q,
+                                   struct cds_wfq_node *node)
+{
+       struct cds_wfq_node **old_tail;
+
+       /*
+        * uatomic_xchg() implicit memory barrier orders earlier stores to data
+        * structure containing node and setting node->next to NULL before
+        * publication.
+        */
+       old_tail = uatomic_xchg(&q->tail, &node->next);
+       /*
+        * At this point, dequeuers see a NULL old_tail->next, which indicates
+        * that the queue is being appended to. The following store will append
+        * "node" to the queue from a dequeuer perspective.
+        */
+       CMM_STORE_SHARED(*old_tail, node);
+}
+
+/*
+ * Waiting for enqueuer to complete enqueue and return the next node
+ */
+static inline struct cds_wfq_node *
+___cds_wfq_node_sync_next(struct cds_wfq_node *node)
+{
+       struct cds_wfq_node *next;
+       int attempt = 0;
+
+       /*
+        * Adaptative busy-looping waiting for enqueuer to complete enqueue.
+        */
+       while ((next = CMM_LOAD_SHARED(node->next)) == NULL) {
+               if (++attempt >= WFQ_ADAPT_ATTEMPTS) {
+                       (void) poll(NULL, 0, WFQ_WAIT); /* Wait for 10ms */
+                       attempt = 0;
+               } else
+                       caa_cpu_relax();
+       }
+
+       return next;
+}
+
+/*
+ * It is valid to reuse and free a dequeued node immediately.
+ *
+ * No need to go on a waitqueue here, as there is no possible state in which the
+ * list could cause dequeue to busy-loop needlessly while waiting for another
+ * thread to be scheduled. The queue appears empty until tail->next is set by
+ * enqueue.
+ */
+static inline struct cds_wfq_node *
+___cds_wfq_dequeue_blocking(struct cds_wfq_queue *q)
+{
+       struct cds_wfq_node *node, *next;
+
+       /*
+        * Queue is empty if it only contains the dummy node.
+        */
+       if (q->head == &q->dummy && CMM_LOAD_SHARED(q->tail) == &q->dummy.next)
+               return NULL;
+       node = q->head;
+
+       next = ___cds_wfq_node_sync_next(node);
+
+       /*
+        * Move queue head forward.
+        */
+       q->head = next;
+       /*
+        * Requeue dummy node if we just dequeued it.
+        */
+       if (node == &q->dummy) {
+               _cds_wfq_node_init(node);
+               _cds_wfq_enqueue(q, node);
+               return ___cds_wfq_dequeue_blocking(q);
+       }
+       return node;
+}
+
+static inline struct cds_wfq_node *
+_cds_wfq_dequeue_blocking(struct cds_wfq_queue *q)
+{
+       struct cds_wfq_node *retnode;
+       int ret;
+
+       ret = pthread_mutex_lock(&q->lock);
+       assert(!ret);
+       retnode = ___cds_wfq_dequeue_blocking(q);
+       ret = pthread_mutex_unlock(&q->lock);
+       assert(!ret);
+       return retnode;
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _URCU_WFQUEUE_STATIC_H */