Documentation for various things.

wgpu-core/src/device/life.rs

@@ -361,10 +361,24 @@ impl<A: hal::Api> LifetimeTracker<A> {
     /// Sort out the consequences of completed submissions.
     ///
     /// Assume that all submissions up through `last_done` have completed.
-    /// Buffers they used are now ready to map. Resources for which they were
-    /// the final use are now ready to free.
     ///
-    /// Return a list of `SubmittedWorkDoneClosure`s to run.
+    /// -   Buffers used by those submissions are now ready to map, if
+    ///     requested. Add any buffers in the submission's [`mapped`] list to
+    ///     [`self.ready_to_map`], where [`LifetimeTracker::handle_mapping`] will find
+    ///     them.
+    ///
+    /// -   Resources whose final use was in those submissions are now ready to
+    ///     free. Add any resources in the submission's [`last_resources`] table
+    ///     to [`self.free_resources`], where [`LifetimeTracker::cleanup`] will find
+    ///     them.
+    ///
+    /// Return a list of [`SubmittedWorkDoneClosure`]s to run.
+    ///
+    /// [`mapped`]: ActiveSubmission::mapped
+    /// [`self.ready_to_map`]: LifetimeTracker::ready_to_map
+    /// [`last_resources`]: ActiveSubmission::last_resources
+    /// [`self.free_resources`]: LifetimeTracker::free_resources
+    /// [`SubmittedWorkDoneClosure`]: crate::device::queue::SubmittedWorkDoneClosure
     #[must_use]
     pub fn triage_submissions(
         &mut self,
@@ -435,6 +449,45 @@ impl<A: hal::Api> LifetimeTracker<A> {
 }
 
 impl<A: HalApi> LifetimeTracker<A> {
+    /// Identify resources to free, according to `trackers` and `self.suspected_resources`.
+    ///
+    /// Given `trackers`, the [`TrackerSet`] belonging to same [`Device`] as
+    /// `self`, and `hub`, the [`Hub`] to which that `Device` belongs:
+    ///
+    /// Remove from `trackers` each resource mentioned in
+    /// [`self.suspected_resources`]. If `trackers` held the final reference to
+    /// that resource, add it to the appropriate free list, to be destroyed by
+    /// the hal:
+    ///
+    /// -   Add resources used by queue submissions still in flight to the
+    ///     [`last_resources`] table of the last such submission's entry in
+    ///     [`self.active`]. When that submission has finished execution. the
+    ///     [`triage_submissions`] method will move them to
+    ///     [`self.free_resources`].
+    ///
+    /// -   Add resources that can be freed right now to [`self.free_resources`]
+    ///     directly. [`LifetimeTracker::cleanup`] will take care of them as
+    ///     part of this poll.
+    ///
+    /// ## Entrained resources
+    ///
+    /// This function finds resources that are used only by other resources
+    /// ready to be freed, and adds those to the free lists as well. For
+    /// example, if there's some texture `T` used only by some texture view
+    /// `TV`, then if `TV` can be freed, `T` gets added to the free lists too.
+    ///
+    /// Since `wgpu-core` resource ownership patterns are acyclic, we can visit
+    /// each type that can be owned after all types that could possibly own
+    /// it. This way, we can detect all free-able objects in a single pass,
+    /// simply by starting with types that are roots of the ownership DAG (like
+    /// render bundles) and working our way towards leaf types (like buffers).
+    ///
+    /// [`Device`]: super::Device
+    /// [`self.suspected_resources`]: LifetimeTracker::suspected_resources
+    /// [`last_resources`]: ActiveSubmission::last_resources
+    /// [`self.active`]: LifetimeTracker::active
+    /// [`triage_submissions`]: LifetimeTracker::triage_submissions
+    /// [`self.free_resources`]: LifetimeTracker::free_resources
     pub(super) fn triage_suspected<G: GlobalIdentityHandlerFactory>(
         &mut self,
         hub: &Hub<A, G>,

wgpu-core/src/device/mod.rs

@@ -277,6 +277,9 @@ pub struct Device<A: hal::Api> {
     command_allocator: Mutex<CommandAllocator<A>>,
     pub(crate) active_submission_index: SubmissionIndex,
     fence: A::Fence,
+
+    /// All live resources allocated with this [`Device`].
+    ///
     /// Has to be locked temporarily only (locked last)
     pub(crate) trackers: Mutex<TrackerSet>,
     // Life tracker should be locked right after the device and before anything else.

wgpu-core/src/hub.rs

@@ -24,8 +24,7 @@ use std::{fmt::Debug, marker::PhantomData, mem, ops};
 /// Use `IdentityManager::default` to construct new instances.
 ///
 /// `IdentityManager` returns `Id`s whose index values are suitable for use as
-/// indices into a vector of information (which you maintain elsewhere) about
-/// those ids' referents:
+/// indices into a `Storage<T>` that holds those ids' referents:
 ///
 /// - Every live id has a distinct index value. Each live id's index selects a
 ///   distinct element in the vector.
@@ -88,10 +87,20 @@ impl IdentityManager {
     }
 }
 
+/// An entry in a `Storage::map` table.
 #[derive(Debug)]
 enum Element<T> {
+    /// There are no live ids with this index.
     Vacant,
+
+    /// There is one live id with this index, allocated at the given
+    /// epoch.
     Occupied(T, Epoch),
+
+    /// Like `Occupied`, but an error occurred when creating the
+    /// resource.
+    ///
+    /// The given `String` is the resource's descriptor label.
     Error(Epoch, String),
 }
 
@@ -112,6 +121,11 @@ impl StorageReport {
 #[derive(Clone, Debug)]
 pub(crate) struct InvalidId;
 
+/// A table of `T` values indexed by the id type `I`.
+///
+/// The table is represented as a vector indexed by the ids' index
+/// values, so you should use an id allocator like `IdentityManager`
+/// that keeps the index values dense and close to zero.
 #[derive(Debug)]
 pub struct Storage<T, I: id::TypedId> {
     map: Vec<Element<T>>,
@@ -269,7 +283,7 @@ impl<T, I: id::TypedId> Storage<T, I> {
 /// If type A implements `Access<B>`, that means we are allowed to proceed
 /// with locking resource `B` after we lock `A`.
 ///
-/// The implenentations basically describe the edges in a directed graph
+/// The implementations basically describe the edges in a directed graph
 /// of lock transitions. As long as it doesn't have loops, we can have
 /// multiple concurrent paths on this graph (from multiple threads) without
 /// deadlocks, i.e. there is always a path whose next resource is not locked

wgpu-core/src/track/mod.rs

@@ -230,9 +230,17 @@ impl<S: ResourceState> ResourceTracker<S> {
         }
     }
 
-    /// Remove the resource from the tracker if it is holding the last reference.
+    /// Remove the resource `id`, only if `self` is holding the last reference to it.
     ///
-    /// Return `true` if we did remove the resource.
+    /// Return `true` if we did remove the resource; the underlying hal resource
+    /// is ready to be freed.
+    ///
+    /// This is generally only meaningful to apply to members of
+    /// [`Device::trackers`], which holds all resources allocated with that
+    /// [`Device`]. Other trackers should never be the final reference.
+    ///
+    /// [`Device`]: crate::device::Device
+    /// [`Device::trackers`]: crate::device::Device::trackers
     pub(crate) fn remove_abandoned(&mut self, id: Valid<S::Id>) -> bool {
         let (index, epoch, backend) = id.0.unzip();
         debug_assert_eq!(backend, self.backend);
@@ -287,7 +295,9 @@ impl<S: ResourceState> ResourceTracker<S> {
         self.map.clear();
     }
 
-    /// Initialize a resource to be used.
+    /// Begin tracking a new resource `id` in state `state`.
+    ///
+    /// Hold `ref_count` in the tracker.
     ///
     /// Returns false if the resource is already registered.
     pub(crate) fn init(
@@ -324,8 +334,18 @@ impl<S: ResourceState> ResourceTracker<S> {
         res.state.query(selector)
     }
 
-    /// Make sure that a resource is tracked, and return a mutable
-    /// reference to it.
+    /// Make sure that a resource is tracked, and return a mutable reference to it.
+    ///
+    /// If the resource isn't tracked, start it in the default state, and take a
+    /// clone of `ref_count`.
+    ///
+    /// The `self_backend` and `map` arguments should be the `backend` and `map`
+    /// fields of a `ResourceTracker`. Ideally this function would just take
+    /// `&mut self` and access those from there, but that would upset the borrow
+    /// checker in some callers, who want to borrow `ResourceTracker::temp`
+    /// alongside our return value. The approach taken here has the caller
+    /// borrow both `map` and `temp`, so the borrow checker can see that they
+    /// don't alias.
     fn get_or_insert<'a>(
         self_backend: wgt::Backend,
         map: &'a mut FastHashMap<Index, Resource<S>>,
@@ -347,6 +367,7 @@ impl<S: ResourceState> ResourceTracker<S> {
         }
     }
 
+    /// Return a mutable reference to `id`'s state.
     fn get<'a>(
         self_backend: wgt::Backend,
         map: &'a mut FastHashMap<Index, Resource<S>>,
@@ -359,7 +380,7 @@ impl<S: ResourceState> ResourceTracker<S> {
         e
     }
 
-    /// Extend the usage of a specified resource.
+    /// Extend the usage of `id`, tracking it if necessary.
     ///
     /// Returns conflicting transition as an error.
     pub(crate) fn change_extend(
@@ -553,6 +574,11 @@ pub enum UsageConflict {
 }
 
 /// A set of trackers for all relevant resources.
+///
+/// `Device` uses this to track all resources allocated from that device.
+/// Resources like `BindGroup`, `CommandBuffer`, and so on that may own a
+/// variety of other resources also use a value of this type to keep track of
+/// everything they're depending on.
 #[derive(Debug)]
 pub(crate) struct TrackerSet {
     pub buffers: ResourceTracker<BufferState>,