remove front-push related code

Now that only the top thread delivers, we can remove the
support for multiple unpending and delivering threads.

src/node.c

@@ -885,17 +885,6 @@ worklist_set_delivered(struct vdp_ctx *vdx, struct bytes_tree *tree,
 	}
 }
 
-/*
- * to minimize lock contention, we walk the tree and gather work on a list
- */
-
-#define set_front(tree, node, wrk) do {					\
-		(tree)->front = node;					\
-		(tree)->front_owner = wrk;				\
-	} while(0)
-
-#define set_end(tree, node) (tree)->end = node;
-
 static void
 worklist_unpend(const struct vdp_ctx *vdx, struct bytes_tree *tree,
     struct node_head *work)
@@ -926,12 +915,8 @@ worklist_unpend(const struct vdp_ctx *vdx, struct bytes_tree *tree,
 		return;
 	}
 
-	AN(tree->front);
-
-	if (tree->front_owner == vdx->wrk)
-		node = tree->front;
-	else
-		node = tree->root;
+	node = tree->front;
+	AN(node);
 
 	/* when starting, we do not want to see any ST_UNPENDING nodes */
 	check = CHK_DELI;
@@ -966,7 +951,7 @@ worklist_unpend(const struct vdp_ctx *vdx, struct bytes_tree *tree,
 				continue;
 
 			VSLdbg(vdx, "bytes_unpend: reached root");
-			set_front(tree, tree->root, vdx->wrk);
+			tree->front = tree->root;
 			if (tree->end != NULL)
 				tree->end->is_end = 1;
 			return;
@@ -976,7 +961,7 @@ worklist_unpend(const struct vdp_ctx *vdx, struct bytes_tree *tree,
 			VSLdbgv(vdx, "bytes_unpend: return at "
 				"node %p state %u - private",
 				node, node->state);
-			set_front(tree, node, vdx->wrk);
+			tree->front = node;
 			return;
 		}
 
@@ -996,15 +981,13 @@ worklist_unpend(const struct vdp_ctx *vdx, struct bytes_tree *tree,
 
 		VSTAILQ_INSERT_TAIL(work, node, unpend);
 		set_unpending(tree, node);
-		set_end(tree, node);
+		tree->end = node;
 
 		// for more iterations, also accept UNPEND
 		// for now, we use any
 		check = CHK_ANY;
 	}
 }
-#undef set_front
-
 void
 tree_deliver(struct vdp_ctx *vdx, struct bytes_tree *tree)
 {
@@ -1014,17 +997,10 @@ tree_deliver(struct vdp_ctx *vdx, struct bytes_tree *tree)
 	CHECK_OBJ_NOTNULL(vdx, VDP_CTX_MAGIC);
 	CHECK_OBJ_NOTNULL(vdx->wrk, WORKER_MAGIC);
 
-	if (tree->unpend_owner != NULL)
-		return;
-
-	tree->unpend_owner = vdx->wrk;
-
 	/*lint -e{506} constant value boolean */
 	do {
 		Lck_AssertHeld(&tree->tree_lock);
 
-		assert(tree->unpend_owner == vdx->wrk);
-
 		VSTAILQ_INIT(&work);
 
 		worklist_unpend(vdx, tree, &work);
@@ -1041,6 +1017,4 @@ tree_deliver(struct vdp_ctx *vdx, struct bytes_tree *tree)
 		}
 		worklist_set_delivered(vdx, tree, &work);
 	} while (1);
-
-	tree->unpend_owner = NULL;
 }

src/node.h

@@ -42,8 +42,6 @@ struct bytes_tree {
 	pthread_cond_t		cond;
 	struct node		*root;
 	struct node		*front;
-	const struct worker	*front_owner;
-	const struct worker	*unpend_owner;
 	// candidate for last ever node
 	struct node		*end;
 	int			end_sent;