util: Add a DAG datastructure.

I keep writing this for various schedulers.

Acked-by: Timothy Arceri <[email protected]>

1 files changed, 154 insertions, 0 deletions

diff --git a/src/util/dag.c b/src/util/dag.c
new file mode 100644
index 00000000000..8f7cdd6348e
--- /dev/null
+++ b/src/util/dag.c
@@ -0,0 +1,154 @@
+/*
+ * Copyright © 2019 Broadcom
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#include "util/set.h"
+#include "util/dag.h"
+
+/**
+ * Adds a directed edge from the parent node to the child.
+ *
+ * Both nodes should have been initialized with dag_init_node().  The edge
+ * list may contain multiple edges to the same child with different data.
+ */
+void
+dag_add_edge(struct dag_node *parent, struct dag_node *child, void *data)
+{
+   util_dynarray_foreach(&parent->edges, struct dag_edge, edge) {
+      if (edge->child == child && edge->data == data)
+         return;
+   }
+   /* Remove the child as a DAG head. */
+   list_delinit(&child->link);
+
+   struct dag_edge edge = {
+      .child = child,
+      .data = data,
+   };
+
+   util_dynarray_append(&parent->edges, struct dag_edge, edge);
+   child->parent_count++;
+}
+
+/* Removes a single edge from the graph, promoting the child to a DAG head.
+ *
+ * Note that calling this other than through dag_prune_head() means that you
+ * need to be careful when iterating the edges of remaining nodes for NULL
+ * children.
+ */
+void
+dag_remove_edge(struct dag *dag, struct dag_edge *edge)
+{
+   if (!edge->child)
+      return;
+
+   struct dag_node *child = edge->child;
+   child->parent_count--;
+   if (child->parent_count == 0)
+      list_addtail(&child->link, &dag->heads);
+
+   edge->child = NULL;
+   edge->data = NULL;
+}
+
+/**
+ * Removes a DAG head from the graph, and moves any new dag heads into the
+ * heads list.
+ */
+void
+dag_prune_head(struct dag *dag, struct dag_node *node)
+{
+   assert(!node->parent_count);
+
+   list_delinit(&node->link);
+
+   util_dynarray_foreach(&node->edges, struct dag_edge, edge) {
+      dag_remove_edge(dag, edge);
+   }
+}
+
+/**
+ * Initializes DAG node (probably embedded in some other datastructure in the
+ * user).
+ */
+void
+dag_init_node(struct dag *dag, struct dag_node *node)
+{
+   util_dynarray_init(&node->edges, dag);
+   list_addtail(&node->link, &dag->heads);
+}
+
+struct dag_traverse_bottom_up_state {
+   struct set *seen;
+   void *data;
+};
+
+static void
+dag_traverse_bottom_up_node(struct dag_node *node,
+                            void (*cb)(struct dag_node *node,
+                                       void *data),
+                            struct dag_traverse_bottom_up_state *state)
+{
+   if (_mesa_set_search(state->seen, node))
+      return;
+
+   util_dynarray_foreach(&node->edges, struct dag_edge, edge) {
+      dag_traverse_bottom_up_node(edge->child, cb, state);
+   }
+
+   cb(node, state->data);
+   _mesa_set_add(state->seen, node);
+}
+
+/**
+ * Walks the DAG from leaves to the root, ensuring that each node is only seen
+ * once its children have been, and each node is only traversed once.
+ */
+void
+dag_traverse_bottom_up(struct dag *dag, void (*cb)(struct dag_node *node,
+                                                   void *data), void *data)
+{
+   struct dag_traverse_bottom_up_state state = {
+      .seen = _mesa_pointer_set_create(NULL),
+      .data = data,
+   };
+
+   list_for_each_entry(struct dag_node, node, &dag->heads, link) {
+      dag_traverse_bottom_up_node(node, cb, &state);
+   }
+
+   ralloc_free(state.seen);
+}
+
+/**
+ * Creates an empty DAG datastructure.
+ */
+struct dag *
+dag_create(void *mem_ctx)
+{
+   struct dag *dag = rzalloc(mem_ctx, struct dag);
+
+   list_inithead(&dag->heads);
+
+   return dag;
+}
+