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[Merged by Bors] - extract topsort logic to a new method, one pass to detect cycles and … #7727

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[Merged by Bors] - extract topsort logic to a new method, one pass to detect cycles and … #7727

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9befeab
extract topsort logic to a new method, one pass to detect cycles and …
shuoli84 Feb 17, 2023
3d5729e
vec::new => vec::with_capacity to reduce realloc. rename nodes_with_c…
shuoli84 Feb 18, 2023
760a686
trigger ci run
shuoli84 Feb 18, 2023
553e8f6
fix clippy
shuoli84 Feb 19, 2023
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81 changes: 39 additions & 42 deletions crates/bevy_ecs/src/schedule/schedule.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,7 @@ use bevy_utils::default;
#[cfg(feature = "trace")]
use bevy_utils::tracing::info_span;
use bevy_utils::{
petgraph::{algo::tarjan_scc, prelude::*},
petgraph::prelude::*,
thiserror::Error,
tracing::{error, warn},
HashMap, HashSet,
Expand Down Expand Up @@ -938,15 +938,9 @@ impl ScheduleGraph {
}

// check hierarchy for cycles
let hier_scc = tarjan_scc(&self.hierarchy.graph);
// PERF: in theory we can skip this contains_cycles because we've already detected cycles
// using calculate_base_sets_and_detect_cycles
if self.contains_cycles(&hier_scc) {
self.report_cycles(&hier_scc);
return Err(ScheduleBuildError::HierarchyCycle);
}

self.hierarchy.topsort = hier_scc.into_iter().flatten().rev().collect::<Vec<_>>();
self.hierarchy.topsort = self
.topsort_graph(&self.hierarchy.graph)
.map_err(|_| ScheduleBuildError::HierarchyCycle)?;

let hier_results = check_graph(&self.hierarchy.graph, &self.hierarchy.topsort);
if self.settings.hierarchy_detection != LogLevel::Ignore
Expand All @@ -962,13 +956,9 @@ impl ScheduleGraph {
self.hierarchy.graph = hier_results.transitive_reduction;

// check dependencies for cycles
let dep_scc = tarjan_scc(&self.dependency.graph);
if self.contains_cycles(&dep_scc) {
self.report_cycles(&dep_scc);
return Err(ScheduleBuildError::DependencyCycle);
}

self.dependency.topsort = dep_scc.into_iter().flatten().rev().collect::<Vec<_>>();
self.dependency.topsort = self
.topsort_graph(&self.dependency.graph)
.map_err(|_| ScheduleBuildError::DependencyCycle)?;

// check for systems or system sets depending on sets they belong to
let dep_results = check_graph(&self.dependency.graph, &self.dependency.topsort);
Expand Down Expand Up @@ -1089,15 +1079,10 @@ impl ScheduleGraph {
}

// topsort
let flat_scc = tarjan_scc(&dependency_flattened);
if self.contains_cycles(&flat_scc) {
self.report_cycles(&flat_scc);
return Err(ScheduleBuildError::DependencyCycle);
}

self.dependency_flattened.topsort = self
.topsort_graph(&dependency_flattened)
.map_err(|_| ScheduleBuildError::DependencyCycle)?;
self.dependency_flattened.graph = dependency_flattened;
self.dependency_flattened.topsort =
flat_scc.into_iter().flatten().rev().collect::<Vec<_>>();

let flat_results = check_graph(
&self.dependency_flattened.graph,
Expand Down Expand Up @@ -1374,31 +1359,43 @@ impl ScheduleGraph {
error!("{}", message);
}

fn contains_cycles(&self, strongly_connected_components: &[Vec<NodeId>]) -> bool {
if strongly_connected_components
.iter()
.all(|scc| scc.len() == 1)
{
return false;
}
/// Get topology sorted [`NodeId`], also ensures the graph contains no cycle
/// returns Err(()) if there are cycles
fn topsort_graph(&self, graph: &DiGraphMap<NodeId, ()>) -> Result<Vec<NodeId>, ()> {
// tarjon_scc's run order is reverse topological order
let mut rev_top_sorted_nodes = Vec::<NodeId>::with_capacity(graph.node_count());
let mut tarjan_scc = bevy_utils::petgraph::algo::TarjanScc::new();
let mut sccs_with_cycle = Vec::<Vec<NodeId>>::new();

true
tarjan_scc.run(graph, |scc| {
// by scc's definition, each scc is the cluster of nodes that they can reach each other
// so scc with size larger than 1, means there is/are cycle(s).
if scc.len() > 1 {
sccs_with_cycle.push(scc.to_vec());
}
rev_top_sorted_nodes.extend_from_slice(scc);
});

if sccs_with_cycle.is_empty() {
// reverse the reverted to get topological order
let mut top_sorted_nodes = rev_top_sorted_nodes;
top_sorted_nodes.reverse();
Ok(top_sorted_nodes)
} else {
self.report_cycles(&sccs_with_cycle);
Err(())
}
}

fn report_cycles(&self, strongly_connected_components: &[Vec<NodeId>]) {
let components_with_cycles = strongly_connected_components
.iter()
.filter(|scc| scc.len() > 1)
.cloned()
.collect::<Vec<_>>();

/// Print detailed cycle messages
fn report_cycles(&self, sccs_with_cycles: &[Vec<NodeId>]) {
let mut message = format!(
"schedule contains at least {} cycle(s)",
components_with_cycles.len()
sccs_with_cycles.len()
);

writeln!(message, " -- cycle(s) found within:").unwrap();
for (i, scc) in components_with_cycles.into_iter().enumerate() {
for (i, scc) in sccs_with_cycles.iter().enumerate() {
let names = scc
.iter()
.map(|id| self.get_node_name(id))
Expand Down