workqueue: add approximate upper bound to queue length

[userspace-rcu.git] / urcu / workqueue-fifo.h

diff --git a/urcu/workqueue-fifo.h b/urcu/workqueue-fifo.h
index a2bbd909fdb1ae3923c8743d155752dceb016802..13d9278a5beca9baa46ea9ef3cc7f3b1981091e0 100644 (file)
--- a/urcu/workqueue-fifo.h
+++ b/urcu/workqueue-fifo.h
@@ -36,6 +36,11 @@ enum urcu_accept_ret {
        URCU_ACCEPT_SHUTDOWN    = 1,
 };
 
+enum urcu_enqueue_ret {
+       URCU_ENQUEUE_OK         = 0,
+       URCU_ENQUEUE_FULL       = 1,
+};
+
 /*
  * We use RCU to steal work from siblings. Therefore, one of RCU flavors
  * need to be included before this header. All worker that participate
@@ -59,6 +64,9 @@ struct urcu_workqueue {
        struct cds_list_head sibling_head;
        pthread_mutex_t sibling_lock;   /* Protect sibling list updates */
 
+       /* Maximum number of work entries (approximate). 0 means infinite. */
+       unsigned long nr_work_max;
+       unsigned long nr_work;          /* Current number of work items */
        bool shutdown;                  /* Shutdown performed */
 };
 
@@ -73,6 +81,7 @@ struct urcu_worker {
        struct urcu_wait_node wait_node;
        /* RCU linked list node of siblings for work stealing. */
        struct cds_list_head sibling_node;
+       struct urcu_workqueue *queue;
        int flags;      /* enum urcu_worker_flags */
 };
 
@@ -81,20 +90,32 @@ enum urcu_worker_flags {
 };
 
 static inline
-void urcu_workqueue_init(struct urcu_workqueue *queue)
+void urcu_workqueue_init(struct urcu_workqueue *queue,
+               unsigned long max_queue_len)
 {
        __cds_wfcq_init(&queue->head, &queue->tail);
        urcu_wait_queue_init(&queue->waitqueue);
        CDS_INIT_LIST_HEAD(&queue->sibling_head);
        pthread_mutex_init(&queue->sibling_lock, NULL);
+       queue->nr_work_max = max_queue_len;
+       queue->nr_work = 0;
        queue->shutdown = false;
 }
 
 static inline
-void urcu_queue_work(struct urcu_workqueue *queue, struct urcu_work *work)
+enum urcu_enqueue_ret urcu_queue_work(struct urcu_workqueue *queue,
+               struct urcu_work *work)
 {
        bool was_empty;
-
+       unsigned long nr_work_max;
+
+       nr_work_max = queue->nr_work_max;
+       if (nr_work_max) {
+               /* Approximate max queue size. */
+               if (uatomic_read(&queue->nr_work) >= nr_work_max)
+                       return URCU_ENQUEUE_FULL;
+               uatomic_inc(&queue->nr_work);
+       }
        cds_wfcq_node_init(&work->node);
 
        /* Enqueue work. */
@@ -118,6 +139,7 @@ void urcu_queue_work(struct urcu_workqueue *queue, struct urcu_work *work)
                (void) urcu_dequeue_wake_single(&queue->waitqueue);
                rcu_read_unlock();      /* Protect stack dequeue */
        }
+       return URCU_ENQUEUE_OK;
 }
 
 static inline
@@ -133,13 +155,15 @@ void __urcu_workqueue_wakeup_all(struct urcu_workqueue *queue)
 }
 
 static inline
-void urcu_worker_init(struct urcu_worker *worker, int flags)
+void urcu_worker_init(struct urcu_workqueue *queue,
+               struct urcu_worker *worker, int flags)
 {
        cds_wfcq_init(&worker->head, &worker->tail);
        worker->flags = flags;
        urcu_wait_node_init(&worker->wait_node, URCU_WAIT_RUNNING);
        worker->own = NULL;
        worker->wait_node.node.next = NULL;
+       worker->queue = queue;
 }
 
 static inline
@@ -358,9 +382,9 @@ end:
 }
 
 static inline
-enum urcu_accept_ret urcu_accept_work(struct urcu_workqueue *queue,
-               struct urcu_worker *worker)
+enum urcu_accept_ret urcu_accept_work(struct urcu_worker *worker)
 {
+       struct urcu_workqueue *queue = worker->queue;
        enum cds_wfcq_ret wfcq_ret;
        bool has_work;
 
@@ -430,15 +454,15 @@ do_work:
 static inline
 struct urcu_work *urcu_dequeue_work(struct urcu_worker *worker)
 {
+       struct urcu_workqueue *queue = worker->queue;
        struct cds_wfcq_node *node;
+       struct urcu_work *work;
 
        if (worker->own) {
-               struct urcu_work *work;
-
                /* Process our own work entry. */
                work = worker->own;
                worker->own = NULL;
-               return work;
+               goto end;
        }
        /*
         * If we are registered for work stealing, we need to dequeue
@@ -459,7 +483,11 @@ struct urcu_work *urcu_dequeue_work(struct urcu_worker *worker)
        }
        if (!node)
                return NULL;
-       return caa_container_of(node, struct urcu_work, node);
+       work = caa_container_of(node, struct urcu_work, node);
+end:
+       if (queue->nr_work_max)
+               uatomic_dec(&queue->nr_work);
+       return work;
 }
 
 static inline