tevent: add tevent_queue_add_entry() and tevent_queue_add_optimize_empty()

This adds more flexible handling for the add operation:

- It allows the caller to remove a tevent_req from the queue
  by calling talloc_free() on the returned tevent_queue_entry.
- It allows the caller to optimize for the empty queue case,
  where it the caller wants to avoid the delay caused by
  the immediate event.

metze

1 files changed, 55 insertions, 2 deletions

diff --git a/lib/tevent/tevent_queue.c b/lib/tevent/tevent_queue.c
index 7737b3e814..4750675802 100644
--- a/lib/tevent/tevent_queue.c
+++ b/lib/tevent/tevent_queue.c
@@ -149,7 +149,8 @@ static struct tevent_queue_entry *tevent_queue_add_internal(
 					struct tevent_context *ev,
 					struct tevent_req *req,
 					tevent_queue_trigger_fn_t trigger,
-					void *private_data)
+					void *private_data,
+					bool allow_direct)
 {
 	struct tevent_queue_entry *e;
 
@@ -171,6 +172,24 @@ static struct tevent_queue_entry *tevent_queue_add_internal(
 		e->triggered = true;
 	}
 
+	if (queue->length > 0) {
+		/*
+		 * if there are already entries in the
+		 * queue do not optimize.
+		 */
+		allow_direct = false;
+	}
+
+	if (req->async.fn != NULL) {
+		/*
+		 * If the callers wants to optimize for the
+		 * empty queue case, call the trigger only
+		 * if there is no callback defined for the
+		 * request yet.
+		 */
+		allow_direct = false;
+	}
+
 	DLIST_ADD_END(queue->list, e, struct tevent_queue_entry *);
 	queue->length++;
 	talloc_set_destructor(e, tevent_queue_entry_destructor);
@@ -183,6 +202,18 @@ static struct tevent_queue_entry *tevent_queue_add_internal(
 		return e;
 	}
 
+	/*
+	 * If allowed we directly call the trigger
+	 * avoiding possible delays caused by
+	 * an immediate event.
+	 */
+	if (allow_direct) {
+		queue->list->triggered = true;
+		queue->list->trigger(queue->list->req,
+				     queue->list->private_data);
+		return e;
+	}
+
 	tevent_schedule_immediate(queue->immediate,
 				  queue->list->ev,
 				  tevent_queue_immediate_trigger,
@@ -200,7 +231,7 @@ bool tevent_queue_add(struct tevent_queue *queue,
 	struct tevent_queue_entry *e;
 
 	e = tevent_queue_add_internal(queue, ev, req,
-				      trigger, private_data);
+				      trigger, private_data, false);
 	if (e == NULL) {
 		return false;
 	}
@@ -208,6 +239,28 @@ bool tevent_queue_add(struct tevent_queue *queue,
 	return true;
 }
 
+struct tevent_queue_entry *tevent_queue_add_entry(
+					struct tevent_queue *queue,
+					struct tevent_context *ev,
+					struct tevent_req *req,
+					tevent_queue_trigger_fn_t trigger,
+					void *private_data)
+{
+	return tevent_queue_add_internal(queue, ev, req,
+					 trigger, private_data, false);
+}
+
+struct tevent_queue_entry *tevent_queue_add_optimize_empty(
+					struct tevent_queue *queue,
+					struct tevent_context *ev,
+					struct tevent_req *req,
+					tevent_queue_trigger_fn_t trigger,
+					void *private_data)
+{
+	return tevent_queue_add_internal(queue, ev, req,
+					 trigger, private_data, true);
+}
+
 void tevent_queue_start(struct tevent_queue *queue)
 {
 	if (queue->running) {