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use super::Liveness;
use illicit::AsContext;
use parking_lot::Mutex;
use std::{
cmp::Ordering,
hash::{Hash, Hasher},
sync::{Arc, Weak},
};
#[derive(Clone, Debug, Default)]
pub(crate) struct DepNode {
inner: Arc<Mutex<InnerDepNode>>,
}
impl DepNode {
pub fn new(dependent: Dependent, revision: u64) -> Self {
let this = Self { inner: Arc::new(Mutex::new(Default::default())) };
this.root_write(dependent, revision);
this
}
/// Mark this node as having been read in the current GC revision. If it hasn't been updated at
/// all before a GC, then its dependencies will inherit its liveness.
pub fn root_read(&self, dependent: Dependent) {
self.inner.lock().root_read(dependent);
}
/// Mark this node as having been written to in the current GC revision. This indicates that the
/// liveness of its dependencies should be assessed on their own, because they'll have had a
/// chance to execute (or not) this revision.
pub fn root_write(&self, dependent: Dependent, revision: u64) {
self.inner.lock().root_write(dependent, revision);
}
pub fn as_dependent(&self) -> Dependent {
Dependent { inner: Arc::downgrade(&self.inner) }
}
pub fn is_known_live(&self) -> bool {
// TODO(#174) find a better way to handle cycles
if let Some(l) = self.inner.try_lock() {
matches!(l.liveness, Liveness::Live)
} else {
false
}
}
fn should_inherit_liveness(&self, current_revision: u64) -> bool {
if let Some(l) = self.inner.try_lock() {
// if the dependent was updated during this revision, then our dependency should only
// consider *its own* liveness. consider the following pseudocode:
//
// cache.cache_with(unique_value(), |_| {
// if externally_modifiable_bool() {
// cache.hold_with((), |v| op(v));
// }
// });
//
// in this case, the inner hold_with() call should not be retained if
// externally_modifiable_bool() returns false. to achieve this, we want the
// cache_with call's liveness to never propagate when the initialization closure
// executes.
l.updated_at_revision != current_revision
} else {
false
}
}
pub fn update_liveness(&mut self, current_revision: u64) {
// TODO(#174) find a better way to handle cycles
if let Some(mut this) = self.inner.try_lock() {
this.update_liveness(current_revision);
}
}
pub fn mark_dead(&mut self) {
self.inner.lock().mark_dead();
}
/// Return the memory address of this `DepNode`.
fn addr(&self) -> usize {
Arc::as_ptr(&self.inner) as *const _ as _
}
}
impl_common_traits_for_type_with_addr!(DepNode);
#[derive(Debug)]
struct InnerDepNode {
liveness: Liveness,
updated_at_revision: u64,
dependents: Vec<Dependent>,
}
impl Default for InnerDepNode {
fn default() -> Self {
Self { liveness: Liveness::Live, updated_at_revision: 0, dependents: Vec::new() }
}
}
impl InnerDepNode {
fn root_read(&mut self, dependent: Dependent) {
self.dependents.push(dependent);
self.liveness = Liveness::Live;
}
fn root_write(&mut self, dependent: Dependent, revision: u64) {
self.dependents.push(dependent);
self.liveness = Liveness::Live;
self.updated_at_revision = revision;
}
/// Check incoming dependents for roots, marking ourselves live if a root
/// exists. Drops stale dependents.
fn update_liveness(&mut self, current_revision: u64) {
self.dependents.sort_unstable();
self.dependents.dedup();
if matches!(self.liveness, Liveness::Live) {
// we've already been here this gc, nothing new to see here
return;
}
let mut has_root = false;
self.dependents.retain(|dependent| {
let mut keep = false;
if let Some(mut dependent) = dependent.upgrade() {
dependent.update_liveness(current_revision);
if dependent.should_inherit_liveness(current_revision) && dependent.is_known_live()
{
has_root = true;
}
keep = true;
}
keep
});
// if we found a transitive root then mark ourselves live
if has_root {
self.liveness = Liveness::Live;
}
}
fn mark_dead(&mut self) {
self.liveness = Liveness::Dead;
}
}
#[derive(Clone, Debug, Default)]
pub(crate) struct Dependent {
inner: Weak<Mutex<InnerDepNode>>,
}
impl Dependent {
/// Return the corresponding `DepNode` if it is still live.
fn upgrade(&self) -> Option<DepNode> {
self.inner.upgrade().map(|inner| DepNode { inner })
}
/// Returns the current incoming `Dependent`. If about to execute a
/// top-level query this will return a null/no-op `Dependent`.
pub fn incoming() -> Self {
if let Ok(dep) = illicit::get::<Self>() {
dep.clone()
} else {
Self::default()
}
}
/// Initialize the dependency query with `self` marked as its immediate
/// dependent.
pub fn init_dependency<R>(self, op: impl FnOnce() -> R) -> R {
self.offer(op)
}
/// Return the memory address of this `Dependent`.
fn addr(&self) -> usize {
self.inner.as_ptr() as *const _ as _
}
}
impl_common_traits_for_type_with_addr!(Dependent);