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/* SPDX-License-Identifier: GPL-2.0-or-later
* Copyright 2015 Blender Foundation. All rights reserved. */
/** \file
* \ingroup depsgraph
*/
#include "intern/builder/deg_builder_cycle.h"
// TOO(sergey): Use some wrappers over those?
#include <cstdio>
#include <cstdlib>
#include "BLI_stack.h"
#include "BLI_utildefines.h"
#include "intern/node/deg_node.h"
#include "intern/node/deg_node_component.h"
#include "intern/node/deg_node_operation.h"
#include "intern/depsgraph.h"
#include "intern/depsgraph_relation.h"
namespace blender::deg {
namespace {
enum eCyclicCheckVisitedState {
/* Not is not visited at all during traversal. */
NODE_NOT_VISITED = 0,
/* Node has been visited during traversal and not in current stack. */
NODE_VISITED = 1,
/* Node has been visited during traversal and is in current stack. */
NODE_IN_STACK = 2,
};
struct StackEntry {
OperationNode *node;
StackEntry *from;
Relation *via_relation;
};
struct CyclesSolverState {
CyclesSolverState(Depsgraph *graph)
: graph(graph), traversal_stack(BLI_stack_new(sizeof(StackEntry), "DEG detect cycles stack"))
{
/* pass */
}
~CyclesSolverState()
{
BLI_stack_free(traversal_stack);
if (num_cycles != 0) {
printf("Detected %d dependency cycles\n", num_cycles);
}
}
Depsgraph *graph;
BLI_Stack *traversal_stack;
int num_cycles = 0;
};
inline void set_node_visited_state(Node *node, eCyclicCheckVisitedState state)
{
node->custom_flags = (node->custom_flags & ~0x3) | (int)state;
}
inline eCyclicCheckVisitedState get_node_visited_state(Node *node)
{
return (eCyclicCheckVisitedState)(node->custom_flags & 0x3);
}
inline void set_node_num_visited_children(Node *node, int num_children)
{
node->custom_flags = (node->custom_flags & 0x3) | (num_children << 2);
}
inline int get_node_num_visited_children(Node *node)
{
return node->custom_flags >> 2;
}
void schedule_node_to_stack(CyclesSolverState *state, OperationNode *node)
{
StackEntry entry;
entry.node = node;
entry.from = nullptr;
entry.via_relation = nullptr;
BLI_stack_push(state->traversal_stack, &entry);
set_node_visited_state(node, NODE_IN_STACK);
}
/* Schedule leaf nodes (node without input links) for traversal. */
void schedule_leaf_nodes(CyclesSolverState *state)
{
for (OperationNode *node : state->graph->operations) {
bool has_inlinks = false;
for (Relation *rel : node->inlinks) {
if (rel->from->type == NodeType::OPERATION) {
has_inlinks = true;
}
}
node->custom_flags = 0;
if (has_inlinks == false) {
schedule_node_to_stack(state, node);
}
else {
set_node_visited_state(node, NODE_NOT_VISITED);
}
}
}
/* Schedule node which was not checked yet for being belong to
* any of dependency cycle.
*/
bool schedule_non_checked_node(CyclesSolverState *state)
{
for (OperationNode *node : state->graph->operations) {
if (get_node_visited_state(node) == NODE_NOT_VISITED) {
schedule_node_to_stack(state, node);
return true;
}
}
return false;
}
bool check_relation_can_murder(Relation *relation)
{
if (relation->flag & RELATION_FLAG_GODMODE) {
return false;
}
return true;
}
Relation *select_relation_to_murder(Relation *relation, StackEntry *cycle_start_entry)
{
/* More or less Russian roulette solver, which will make sure only
* specially marked relations are kept alive.
*
* TODO(sergey): There might be better strategies here. */
if (check_relation_can_murder(relation)) {
return relation;
}
StackEntry *current = cycle_start_entry;
OperationNode *to_node = (OperationNode *)relation->to;
while (current->node != to_node) {
if (check_relation_can_murder(current->via_relation)) {
return current->via_relation;
}
current = current->from;
}
return relation;
}
/* Solve cycles with all nodes which are scheduled for traversal. */
void solve_cycles(CyclesSolverState *state)
{
BLI_Stack *traversal_stack = state->traversal_stack;
while (!BLI_stack_is_empty(traversal_stack)) {
StackEntry *entry = (StackEntry *)BLI_stack_peek(traversal_stack);
OperationNode *node = entry->node;
bool all_child_traversed = true;
const int num_visited = get_node_num_visited_children(node);
for (int i = num_visited; i < node->outlinks.size(); i++) {
Relation *rel = node->outlinks[i];
if (rel->to->type == NodeType::OPERATION) {
OperationNode *to = (OperationNode *)rel->to;
eCyclicCheckVisitedState to_state = get_node_visited_state(to);
if (to_state == NODE_IN_STACK) {
string cycle_str = " " + to->full_identifier() + " depends on\n " +
node->full_identifier() + " via '" + rel->name + "'\n";
StackEntry *current = entry;
while (current->node != to) {
BLI_assert(current != nullptr);
cycle_str += " " + current->from->node->full_identifier() + " via '" +
current->via_relation->name + "'\n";
current = current->from;
}
printf("Dependency cycle detected:\n%s", cycle_str.c_str());
Relation *sacrificial_relation = select_relation_to_murder(rel, entry);
sacrificial_relation->flag |= RELATION_FLAG_CYCLIC;
++state->num_cycles;
}
else if (to_state == NODE_NOT_VISITED) {
StackEntry new_entry;
new_entry.node = to;
new_entry.from = entry;
new_entry.via_relation = rel;
BLI_stack_push(traversal_stack, &new_entry);
set_node_visited_state(node, NODE_IN_STACK);
all_child_traversed = false;
set_node_num_visited_children(node, i);
break;
}
}
}
if (all_child_traversed) {
set_node_visited_state(node, NODE_VISITED);
BLI_stack_discard(traversal_stack);
}
}
}
} // namespace
void deg_graph_detect_cycles(Depsgraph *graph)
{
CyclesSolverState state(graph);
/* First we solve cycles which are reachable from leaf nodes. */
schedule_leaf_nodes(&state);
solve_cycles(&state);
/* We are not done yet. It is possible to have closed loop cycle,
* for example A -> B -> C -> A. These nodes were not scheduled
* yet (since they all have inlinks), and were not traversed since
* nobody else points to them. */
while (schedule_non_checked_node(&state)) {
solve_cycles(&state);
}
}
} // namespace blender::deg
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