Don't drop messages from workers that have already been closed (#11913)

When `worker.terminate()` is called, the spec requires that the
corresponding port message queue is emptied, so no messages can be
received after the call, even if they were sent from the worker before
it was terminated.

The spec doesn't require this of `self.close()`, and since Deno uses
different channels to send messages and to notify that the worker was
closed, messages might still arrive after the worker is known to be
closed, which are currently being dropped. This change fixes that.

The fix involves two parts: one on the JS side and one on the Rust side.
The JS side was using the `#terminated` flag to keep track of whether
the worker is known to be closed, without distinguishing whether further
messages should be dropped or not. This PR changes that flag to an
enum `#state`, which can be one of `"RUNNING"`, `"CLOSED"` or
`"TERMINATED"`.

The Rust side was removing the `WorkerThread` struct from the workers
table when a close control was received, regardless of whether there
were any messages left to read, which made any subsequent calls to
`op_host_recv_message` to return `Ok(None)`, as if there were no more
mesasges. This change instead waits for both a close control and for
the message channel's sender to be closed before the worker thread is
removed from the table.

1 files changed, 57 insertions, 14 deletions

diff --git a/runtime/ops/worker_host.rs b/runtime/ops/worker_host.rs
index d80a39502..829681ab6 100644
--- a/runtime/ops/worker_host.rs
+++ b/runtime/ops/worker_host.rs
@@ -67,6 +67,12 @@ pub struct CreateWebWorkerCbHolder(Arc<CreateWebWorkerCb>);
 pub struct WorkerThread {
   join_handle: JoinHandle<Result<(), AnyError>>,
   worker_handle: WebWorkerHandle,
+
+  // A WorkerThread that hasn't been explicitly terminated can only be removed
+  // from the WorkersTable once close messages have been received for both the
+  // control and message channels. See `close_channel`.
+  ctrl_closed: bool,
+  message_closed: bool,
 }
 
 pub type WorkersTable = HashMap<WorkerId, WorkerThread>;
@@ -553,6 +559,8 @@ fn op_create_worker(
   let worker_thread = WorkerThread {
     join_handle,
     worker_handle: worker_handle.into(),
+    ctrl_closed: false,
+    message_closed: false,
   };
 
   // At this point all interactions with worker happen using thread
@@ -582,19 +590,49 @@ fn op_host_terminate_worker(
   Ok(())
 }
 
-/// Try to remove worker from workers table - NOTE: `Worker.terminate()`
-/// might have been called already meaning that we won't find worker in
-/// table - in that case ignore.
-fn try_remove_and_close(state: Rc<RefCell<OpState>>, id: WorkerId) {
+enum WorkerChannel {
+  Ctrl,
+  Messages,
+}
+
+/// Close a worker's channel. If this results in both of a worker's channels
+/// being closed, the worker will be removed from the workers table.
+fn close_channel(
+  state: Rc<RefCell<OpState>>,
+  id: WorkerId,
+  channel: WorkerChannel,
+) {
+  use std::collections::hash_map::Entry;
+
   let mut s = state.borrow_mut();
   let workers = s.borrow_mut::<WorkersTable>();
-  if let Some(worker_thread) = workers.remove(&id) {
-    worker_thread.worker_handle.terminate();
-    worker_thread
-      .join_handle
-      .join()
-      .expect("Worker thread panicked")
-      .expect("Panic in worker event loop");
+
+  // `Worker.terminate()` might have been called already, meaning that we won't
+  // find the worker in the table - in that case ignore.
+  if let Entry::Occupied(mut entry) = workers.entry(id) {
+    let terminate = {
+      let worker_thread = entry.get_mut();
+      match channel {
+        WorkerChannel::Ctrl => {
+          worker_thread.ctrl_closed = true;
+          worker_thread.message_closed
+        }
+        WorkerChannel::Messages => {
+          worker_thread.message_closed = true;
+          worker_thread.ctrl_closed
+        }
+      }
+    };
+
+    if terminate {
+      let worker_thread = entry.remove();
+      worker_thread.worker_handle.terminate();
+      worker_thread
+        .join_handle
+        .join()
+        .expect("Worker thread panicked")
+        .expect("Panic in worker event loop");
+    }
   }
 }
 
@@ -620,13 +658,13 @@ async fn op_host_recv_ctrl(
   if let Some(event) = maybe_event {
     // Terminal error means that worker should be removed from worker table.
     if let WorkerControlEvent::TerminalError(_) = &event {
-      try_remove_and_close(state, id);
+      close_channel(state, id, WorkerChannel::Ctrl);
     }
     return Ok(event);
   }
 
   // If there was no event from worker it means it has already been closed.
-  try_remove_and_close(state, id);
+  close_channel(state, id, WorkerChannel::Ctrl);
   Ok(WorkerControlEvent::Close)
 }
 
@@ -646,7 +684,12 @@ async fn op_host_recv_message(
       return Ok(None);
     }
   };
-  worker_handle.port.recv(state).await
+
+  let ret = worker_handle.port.recv(state.clone()).await?;
+  if ret.is_none() {
+    close_channel(state, id, WorkerChannel::Messages);
+  }
+  Ok(ret)
 }
 
 /// Post message to guest worker as host