From 85b9b7222d4a949cd673bf4ecf9c7278b5613c88 Mon Sep 17 00:00:00 2001
From: Julian Orth <ju.orth@gmail.com>
Date: Fri, 13 Mar 2026 12:56:17 +0100
Subject: [PATCH] object_drop_queue: add new utility

---
 src/compositor.rs              |  2 +
 src/state.rs                   |  4 ++
 src/utils.rs                   |  1 +
 src/utils/object_drop_queue.rs | 84 ++++++++++++++++++++++++++++++++++
 4 files changed, 91 insertions(+)
 create mode 100644 src/utils/object_drop_queue.rs

diff --git a/src/compositor.rs b/src/compositor.rs
index 27a96be2..fa6777b5 100644
--- a/src/compositor.rs
+++ b/src/compositor.rs
@@ -72,6 +72,7 @@ use {
             fdcloser::FdCloser,
             nice::{did_elevate_scheduler, elevate_scheduler},
             numcell::NumCell,
+            object_drop_queue::ObjectDropQueue,
             oserror::OsError,
             queue::AsyncQueue,
             rc_eq::RcEq,
@@ -390,6 +391,7 @@ fn start_compositor2(
         supports_presentation_feedback: Default::default(),
         eventfd_cache,
         lazy_event_sources: Default::default(),
+        bo_drop_queue: Rc::new(ObjectDropQueue::new(&ring)),
     });
     state.tracker.register(ClientId::from_raw(0));
     create_dummy_output(&state);
diff --git a/src/state.rs b/src/state.rs
index 652f50a0..5788a95f 100644
--- a/src/state.rs
+++ b/src/state.rs
@@ -1,6 +1,7 @@
 use {
     crate::{
         acceptor::Acceptor,
+        allocator::BufferObject,
         async_engine::{AsyncEngine, SpawnedFuture},
         backend::{
             Backend, BackendConnectorState, BackendConnectorStateSerials, BackendDrmDevice,
@@ -115,6 +116,7 @@ use {
             hash_map_ext::HashMapExt,
             linkedlist::LinkedList,
             numcell::NumCell,
+            object_drop_queue::ObjectDropQueue,
             queue::AsyncQueue,
             refcounted::RefCounted,
             run_toplevel::RunToplevel,
@@ -292,6 +294,7 @@ pub struct State {
     pub supports_presentation_feedback: Cell<bool>,
     pub eventfd_cache: Rc<EventfdCache>,
     pub lazy_event_sources: Rc<LazyEventSources>,
+    pub bo_drop_queue: Rc<ObjectDropQueue<Rc<dyn BufferObject>>>,
 }
 
 // impl Drop for State {
@@ -1154,6 +1157,7 @@ impl State {
         self.wait_for_syncobj.clear();
         self.xdg_surface_configure_events.clear();
         self.lazy_event_sources.clear();
+        self.bo_drop_queue.kill();
     }
 
     pub fn remove_toplevel_id(&self, id: ToplevelIdentifier) {
diff --git a/src/utils.rs b/src/utils.rs
index 7c956c82..31cadb59 100644
--- a/src/utils.rs
+++ b/src/utils.rs
@@ -31,6 +31,7 @@ pub mod nice;
 pub mod nonblock;
 pub mod num_cpus;
 pub mod numcell;
+pub mod object_drop_queue;
 pub mod on_change;
 pub mod on_drop_event;
 pub mod once;
diff --git a/src/utils/object_drop_queue.rs b/src/utils/object_drop_queue.rs
new file mode 100644
index 00000000..2ce1ea45
--- /dev/null
+++ b/src/utils/object_drop_queue.rs
@@ -0,0 +1,84 @@
+use {
+    crate::{
+        io_uring::{IoUring, PendingPoll, PollCallback},
+        utils::{errorfmt::ErrorFmt, oserror::OsError, stack::Stack},
+    },
+    std::{
+        cell::{Cell, RefCell},
+        rc::Rc,
+    },
+    uapi::{OwnedFd, c::c_short},
+};
+
+pub struct ObjectDropQueue<T> {
+    ring: Rc<IoUring>,
+    killed: Cell<bool>,
+    pending: RefCell<Vec<Option<(T, PendingPoll)>>>,
+    stack: Stack<Rc<Pollable<T>>>,
+}
+
+struct Pollable<T> {
+    queue: Rc<ObjectDropQueue<T>>,
+    idx: usize,
+}
+
+impl<T> ObjectDropQueue<T> {
+    pub fn new(ring: &Rc<IoUring>) -> Self {
+        Self {
+            ring: ring.clone(),
+            killed: Default::default(),
+            pending: Default::default(),
+            stack: Default::default(),
+        }
+    }
+
+    #[expect(dead_code)]
+    pub fn push(self: &Rc<Self>, fd: &Rc<OwnedFd>, t: T)
+    where
+        T: 'static,
+    {
+        if self.killed.get() {
+            return;
+        }
+        let pending = &mut *self.pending.borrow_mut();
+        let pollable = match self.stack.pop() {
+            Some(p) => p,
+            None => {
+                let pollable = Rc::new(Pollable {
+                    queue: self.clone(),
+                    idx: pending.len(),
+                });
+                pending.push(None);
+                pollable
+            }
+        };
+        let idx = pollable.idx;
+        match self.ring.readable_external(fd, pollable) {
+            Ok(p) => {
+                pending[idx] = Some((t, p));
+            }
+            Err(e) => {
+                log::error!("Could not register object: {}", ErrorFmt(e));
+            }
+        }
+    }
+
+    pub fn kill(&self) {
+        self.killed.set(true);
+        self.pending.take();
+        self.stack.take();
+    }
+}
+
+impl<T> PollCallback for Pollable<T> {
+    fn completed(self: Rc<Self>, res: Result<c_short, OsError>) {
+        if let Err(e) = res {
+            log::error!("Could not wait for fd to become readable: {}", ErrorFmt(e));
+        }
+        let q = &self.queue;
+        if !q.killed.get() {
+            q.pending.borrow_mut()[self.idx] = None;
+            q.stack.push(self.clone());
+        }
+    }
+}