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use crate::{
NodeId,
collections::{HashMap, HashSet},
graph::Parent,
tensor::NodeRefCount,
};
use alloc::{borrow::ToOwned, sync::Arc, vec, vec::Vec};
use core::mem;
#[derive(Default, Debug)]
pub struct GraphMemoryManagement {
nodes: HashMap<NodeRefCount, Vec<NodeId>>,
leaves: HashSet<NodeId>,
statuses: HashMap<NodeId, NodeMemoryStatus>,
}
#[derive(Debug, Clone, PartialEq)]
enum NodeMemoryStatus {
Useful,
Unavailable,
Unknown,
}
impl GraphMemoryManagement {
pub fn extend(&mut self, other: Self) {
self.nodes.extend(other.nodes);
self.leaves.extend(other.leaves);
self.statuses.extend(other.statuses);
}
/// Register a new node with its parent.
pub fn register(&mut self, node: NodeRefCount, parents: &[Parent]) {
let node_id = *node.as_ref();
for parent in parents.iter() {
self.leaves.remove(&parent.id);
}
self.leaves.insert(node_id);
self.nodes
.insert(node, parents.iter().map(|p| p.id).collect());
}
/// Free the node from the state.
pub fn consume_node(&mut self, node_id: NodeId) {
if !self.is_referenced(node_id) {
self.leaves.remove(&node_id);
self.nodes.remove(&node_id);
}
}
/// Free all nodes whose backward call has become impossible
///
/// This function goes into three steps, which must happen for all leaves
/// before going into the next step. Then it deletes what can be safely deleted
pub(crate) fn free_unavailable_nodes(&mut self, mut on_free_graph: impl FnMut(&NodeId)) {
let leaves = self.leaves.clone();
let mut new_leaves = HashSet::new();
let mut deletables = Vec::new();
// When consuming nodes with a backward pass, some other backward passes become
// unavailable because some of their parents have been consumed. They are
// identified here.
for leaf in leaves.clone() {
self.unavailable_propagation(leaf);
}
// Among the available nodes that remain, some may be useless if no
// available node with a tensor reference exist in their descendance.
// But some may seem useless from some leaf but be useful from another one,
// hence the need to iterate on all leaves.
self.useful_propagation(leaves.clone());
// New leaves are the roots of a useful backward sub-tree.
// Deletables are everything not marked as useful.
for leaf in leaves {
self.identify_leaves_and_deletables(leaf, &mut new_leaves, &mut deletables);
}
// Replace leaves by the new ones and delete everything not useful anymore
mem::swap(&mut self.leaves, &mut new_leaves);
self.clear_unused_roots(&mut deletables);
self.statuses.clear();
for node_to_delete in deletables {
self.nodes.remove(&node_to_delete);
on_free_graph(&node_to_delete)
}
}
pub(crate) fn free_unused_roots(&mut self, mut on_free_graph: impl FnMut(&NodeId)) {
let mut deletables = Vec::new();
self.clear_unused_roots(&mut deletables);
for node_id in deletables {
self.nodes.remove(&node_id);
on_free_graph(&node_id);
}
}
fn clear_unused_roots(&self, to_delete: &mut Vec<NodeId>) {
for (id, parents) in self.nodes.iter() {
let is_useful = matches!(
self.statuses.get(id.as_ref()),
Some(NodeMemoryStatus::Useful)
);
// Check if parents are either empty or absent from self.nodes
let parents_absent = parents.iter().all(|p| !self.nodes.contains_key(p));
if !is_useful && Arc::strong_count(id) == 1 && parents_absent {
to_delete.push(*id.as_ref())
}
}
}
fn unavailable_propagation(&mut self, node_id: NodeId) -> NodeMemoryStatus {
// If already visited
if let Some(status) = self.statuses.get(&node_id) {
return status.clone();
}
match self.nodes.get(&node_id).cloned() {
// If node exists and any of its parents is unavailable, it is unavailable as well
// If node exists but the parents vec is empty, it is a tensor that never had parents;
// the status remains unknown
Some(parents) => {
let mut node_status = NodeMemoryStatus::Unknown;
for parent in parents {
let parent_status = self.unavailable_propagation(parent);
if let NodeMemoryStatus::Unavailable = parent_status {
node_status = NodeMemoryStatus::Unavailable;
}
}
self.statuses.insert(node_id, node_status.clone());
node_status
}
// If node does not exist, it was
// deleted, so this and all its descendants are unavailable
None => {
self.statuses.insert(node_id, NodeMemoryStatus::Unavailable);
NodeMemoryStatus::Unavailable
}
}
}
fn useful_propagation(&mut self, leaves: HashSet<NodeId>) {
// Accumulate visited nodes
let mut explored = HashSet::new();
let mut tagged_useful = HashSet::new();
// Queue of nodes to visit
let mut to_tag_useful = PopNodeSet::default();
let mut to_explore = PopNodeSet::new(leaves);
// Utility function to iterate over a node's parents
let parents = |node_id| {
self.nodes
.get(&node_id)
.cloned()
.unwrap_or_default()
.into_iter()
};
loop {
// Pop a node id, greedily looking at tag_useful ones first
let (node_id, status) = match to_tag_useful.pop() {
Some(node_id) => (node_id, NodeMemoryStatus::Useful),
None => match to_explore.pop() {
Some(node_id) => {
let node_status = self
.statuses
.get(&node_id)
.expect("All nodes should have received a status during unavailable_propagation")
.to_owned();
if let NodeMemoryStatus::Unknown = node_status {
match self.is_referenced(node_id) {
true => (node_id, NodeMemoryStatus::Useful),
false => (node_id, NodeMemoryStatus::Unknown),
}
} else {
(node_id, node_status)
}
}
None => {
// There are no nodes in the queues anymore
break;
}
},
};
match status {
NodeMemoryStatus::Useful => {
tagged_useful.insert(node_id);
for parent in parents(node_id) {
// The node can be explored, as long as it's not already tagged useful
if !(tagged_useful.contains(&parent) || to_tag_useful.contains(&parent)) {
to_tag_useful.insert(parent);
}
}
}
_ => {
explored.insert(node_id);
for parent in parents(node_id) {
if !(explored.contains(&parent) || to_explore.contains(&parent)) {
to_explore.insert(parent);
}
}
}
}
self.statuses.insert(node_id, status);
}
}
fn identify_leaves_and_deletables(
&self,
leaf_id: NodeId,
new_leaves: &mut HashSet<NodeId>,
to_delete: &mut Vec<NodeId>,
) {
let mut visited = HashSet::new();
let mut to_visit = vec![leaf_id];
while let Some(node_id) = to_visit.pop() {
visited.insert(node_id);
match self
.statuses
.get(&node_id)
.expect("Node should have status")
{
NodeMemoryStatus::Useful => {
new_leaves.insert(node_id);
}
_ => {
to_delete.push(node_id);
for parent in self
.nodes
.get(&node_id)
.cloned()
.unwrap_or_default()
.into_iter()
{
if !visited.contains(&parent) {
to_visit.push(parent);
}
}
}
};
}
}
fn is_referenced(&self, node_id: NodeId) -> bool {
match self.nodes.get_key_value(&node_id) {
Some((key, _value)) => Arc::strong_count(key) > 1,
None => panic!("Node should be in the nodes map"),
}
}
pub(crate) fn maybe_useful(&self) -> bool {
self.nodes.keys().any(|node| Arc::strong_count(node) > 1)
}
}
/// Wrapper over hash set for fast popping of any node
#[derive(new, Default)]
struct PopNodeSet {
hash_set: HashSet<NodeId>,
}
impl PopNodeSet {
#[inline(always)]
fn pop(&mut self) -> Option<NodeId> {
self.hash_set
.iter()
.next()
.copied()
.and_then(|node_id| self.hash_set.take(&node_id))
}
#[inline(always)]
fn contains(&self, node_id: &NodeId) -> bool {
self.hash_set.contains(node_id)
}
#[inline(always)]
fn insert(&mut self, node_id: NodeId) {
self.hash_set.insert(node_id);
}
}