Use asyncio (2) by rwols · Pull Request #3021 · sublimelsp/LSP

rwols · 2026-09-04T18:18:28Z

This PR switches the codebase to using async def functions and asyncio. The loop provider is sublime_aio.

should be merged (and released) at the same time as:

The main driver for doing this is to decrease the thread usage of this plugin from O(n) to O(1) threads, where n is the number of language servers running. The secondary driver is syntax sugar.

Why is this PR so large? Please read: What color is your function?

Continuation of: #2880

…se later

Also write the rest of the requests in terms of Session.request

- Add sublime.set_timeout executor wrapper - Make all request handlers `async` - Define a CancellableInflightStreamingRequest class that enables `async for` syntax - Start inheriting DocumentSyncListener from sublime_aio.ViewEventListener (This one doesn't work yet) The state is fairly broken at this point.

… resolving

- Typo fixes: various typos fixed - Session starting logic: only partially. Sessions attach to listeners now, but, only one session starts while multiple should start. I think the solution is now to simply start all the `WindowManager.start` coroutines at the same time. They'll wait on each other via the `WindowManager._start_lock`. - Fix folding ranges using `send_request_async` while it should be using `send_request` (because it calls that from the main thread). - Requests seem to be generally working *provided pull diagnostics are not used*. Testing with clangd works, testing with pyright shows requests not working and something fundamental being stuck somewhere. Broken: - didOpen/didClose is sent two times - Workspace/pull diagnostics are broken - There's various `sublime.set_timeout_async` calls throughout the codebase, but we're now at the point where that's "wrong". I hope to find-and-replace these invocations with `sublime_aio.call_soon_threadsafe`.

…o.py

…tion

…tops

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rchl · 2026-09-06T20:05:24Z

+        if task := self.create_task_threadsafe(
+            self.run_command(command, progress=progress, view=view, is_refactoring=is_refactoring)
+        ):
+            return Promise.wrap_task(task)
+        raise RuntimeError("unable to schedule task")


self.create_task_threadsafe doesn't return anything so this will always throw.

rchl · 2026-09-06T20:08:22Z

            self._plugin = self._plugin_class(weakref.ref(self))
        self.transport = transport
        self.working_directory = working_directory
-        self._variables = variables


This line was dropped but there is still code that references self._variables which now will always be empty.

rchl · 2026-09-06T20:11:21Z

+                return
+            self.workspace_diagnostics_pending_responses[identifier] = None
+            return
+        self._on_workspace_diagnostics_async(identifier, response, reset_pending_response=False)


All callers now call _on_workspace_diagnostics_async with reset_pending_response=False. That doesn't seem right.

rchl · 2026-09-06T20:12:24Z

                    request_id = int(token[len(_WORK_DONE_PROGRESS_PREFIX):])
                    request = self._response_handlers[request_id][0]
-                    self._invoke_views(request, "on_request_progress", request_id, params)
+                    lambda: self._invoke_views(request, "on_request_progress", request_id, params)


This syntax doesn't quite make sense - lambda created and discarded immediately?

rchl · 2026-09-06T20:13:00Z

+            if os.path.isfile(new_path):  # noqa: ASYNC240
+                if options.get('overwrite') and os.path.isfile(old_path):  # noqa: ASYNC240
+                    await delete_file(new_path)
+                    await _continue(rename_file(old_path, new_path))


Missing return?

rchl · 2026-09-06T20:17:04Z

+            while os.path.exists(path) and attempts < self._FILE_DELETED_MAX_CHECK_ATTEMPTS:  # noqa: ASYNC240
+                await asyncio.sleep(0.1)
+                attempts += 1
+            if attempts >= self._FILE_DELETED_MAX_CHECK_ATTEMPTS:
+                raise asyncio.TimeoutError(f"Timeout waiting for deletion of {path}")


There should be a final check after the last sleep. Otherwise that last sleep is pointless.

rchl · 2026-09-06T20:18:50Z

+        with self._threading_condition:
+            run_on_asyncio_thread(set_request_id)
+            self._threading_condition.wait_for(lambda: request_id is not None)


This will deadlock when request errors?

rchl · 2026-09-06T20:20:12Z

+                return cast('ApplyWorkspaceEditResult', {}), cast('WorkspaceEditSummary', {})
+            return x
+
+        if task := self.create_task(self.apply_workspace_edit(edit, label=label, is_refactoring=is_refactoring)):


Should this use a threadsafe variant to create task?

rchl · 2026-09-07T19:50:20Z

-    def purge_changes_async(self) -> None:
+    def purge_changes(self) -> asyncio.Future[list[BaseException | None]]:
        raise NotImplementedError

    @abstractmethod
-    def trigger_on_pre_save_async(self) -> None:
+    def trigger_on_pre_save(self) -> asyncio.Future[list[BaseException | None]]:


Is there specific reason for annotating the return value with asyncio.Future vs. just using async keyword on the method?

Some methods here do it one way and some do another.

The reason for returning asyncio.Future is that this function will unconditionally do that.

In a coroutine, say

async def trigger_on_pre_save(self) -> list[BaseException | None]: ...

you can conditionally return early, or conditionally await something and suspend. You need the function to be a coroutine function in that case.

But unconditionally, always, returning something awaitable, such a function does not have to be a coroutine function but can be a "simpler" regular function that returns the Future.

And why do that? What is the benefit of trigger_on_pre_save implementation returning a Future rather than awaiting it itself?

rchl · 2026-09-07T19:55:11Z

+    _id: int | None
+    _weaksession: weakref.ref[Session]


Why declare private properties this way? I would understand public, to act as a documentation, but for private this seems unnecessary. It would be better to let the type be inferred from the assignment in __init__ or assign explicit type there (can matter if class is overridden).

rchl · 2026-09-07T20:18:30Z

-    ) -> None:
+        transport: TransportWrapper
+    ) -> InitializeResult | Error:
+        loop = asyncio.get_running_loop()


Is there a particular reason why loop variable is assigned on the first line if it's only needed in the last line?

rchl · 2026-09-07T20:25:49Z

-                task: PackagedTask[R | Error | None] = Promise.packaged_task()
+                task: PackagedTask[LSPAny | Error | None] = Promise.packaged_task()
                promise, resolve = task
                if self._plugin.on_pre_server_command(command, lambda: resolve(None)):
-                    return promise
-                resolve(None)
+                    return cast("LSPAny", await promise)


There was a resolve(None) here before. I think it should still be here. Not sure if not having it would prevent GC but even if not, better to clean after ourselves.

rchl · 2026-09-07T20:38:34Z

+        code_action_or_error = await self._maybe_resolve_code_action(code_action, view)
+        if isinstance(code_action_or_error, Error):
+            return code_action_or_error
+        return await self._apply_code_action(code_action_or_error, view)


_apply_code_action does handle Error too. If you've made decision here to handle error at call-site then we can now remove Error handling from _apply_code_action.

rchl · 2026-09-07T20:39:21Z

+            return await self._open_file_uri(uri, r, flags, group)
+
        # Try to find a pre-existing session-buffer
        if sb := self.get_session_buffer_for_uri_async(uri):
            view = sb.get_view_in_group(group)
            self.window.focus_view(view)
            if r:
                center_selection(view, r)
-            return Promise.resolve(view)
+            return view
        if scheme == 'res':
-            return self._open_res_uri_async(uri, r, group)
+            return await self._open_res_uri(uri, r, group)
+
        if scheme == 'untitled':  # VSCode specific URI scheme for unsaved buffers


Can we remove empty lines?

rchl · 2026-09-07T20:46:56Z

+            return
        if isinstance(code_action, Error):
-            # TODO: our promise must be able to handle exceptions (or, wait until we can use coroutines)
+            # TODO: do something with the error?


don't see what else than printing an error we can do

rchl · 2026-09-07T20:54:42Z

+            x: tuple[ApplyWorkspaceEditResult, WorkspaceEditSummary] | BaseException,
+        ) -> tuple[ApplyWorkspaceEditResult, WorkspaceEditSummary]:
+            if isinstance(x, BaseException):
+                return cast('ApplyWorkspaceEditResult', {}), cast('WorkspaceEditSummary', {})


Forcing types could lead to crashes. This might be better:

Suggested change

return cast('ApplyWorkspaceEditResult', {}), cast('WorkspaceEditSummary', {})

return {"applied": False}, {"created_files": 0, "edited_files": 0, "total_changes": 0}

rwols added 30 commits April 22, 2026 20:17

Remove code in server.py, I really screwed up the merge but will reba…

6cad098

…se later

refactor Promise.__await__

1597782

Add more comments to _SetTimeoutAsyncExecutor

cc642f4

Rename Session._invoke_views -> Session._invoke_views_async

cea0e99

Also write the rest of the requests in terms of Session.request

debugging sublime_aio.ViewEventListener

472705b

Merge branch 'main' into feat/asyncio

ea34714

Fix calls

069ed50

More fix calls

776749a

More work. Some diagnostics show intermittently. Request logic is not…

0227877

… resolving

Tweaks to pull diagnostics handling

2649a6f

Restore method names

54af917

Forgot import

1a4589c

Restore more method names

900f721

ResponseException is not needed, we already have Error

35621cf

Merge branch 'main' into feat/asyncio

dbf4d7d

More rename reverts

f3b2f84

Add more tracing for understanding why requests are not resolving

a9c1692

Start fixing up 'goto' functionality

7004df5

debugging

d27aa93

We have something working

341ff99

Start fixing diagnostic errors because diagnostics work

4ed4e3f

Remove trace() calls

7aba65e

Remove trace() calls

e3ccba2

Remove trace() calls

c2c2a8c

Fixups

af561a8

Remove trace() calls and fixup type hints

7260c90

Reintroduce request_code_actions_async for SessionBuffer

a60ddd2

Consolidate sublime_aio & asyncio functions/classes in plugin/core/ai…

23210e3

…o.py

rwols and others added 24 commits July 28, 2026 21:45

Fix ancient completionItem/resolve rendering bug and simplify

cb2913b

Merge branch 'main' into feat/asyncio

af4235b

update docblock for @uri_handler

f67aa98

Fix ancient completionItem/resolve rendering bug, part 2

73285fd

Rename: _MAX_WAIT_ATTEMPTS -> _FILE_DELETED_MAX_CHECK_ATTEMPTS

c3b112d

Fix: make Session.{execute_command,run_code_action_async} threadsafe

91c495d

Fix: make DocumentSyncListener.purge_changes_async threadsafe

936736e

Merge branch 'main' into feat/asyncio

9eb5a7b

Rename: CancellableRequest -> RequestController

e1f441c

Rename: CancellableInflightRequest -> CancellableRequest

a81bef5

Merge branch 'main' into feat/asyncio

1d0b821

Organize imports

02fcfd3

Merge branch 'main' into feat/asyncio

bff80da

Rename: 'cancellable' -> 'controller' (variable/param names)

537a541

Remove: ExceptionPolicy IntEnum

92bc614

Change Signature: tick(int) -> tick()

308adf6

Remove redundant type annotation

84fc088

Change Signature: show_summary_message last arg cannot be a BaseExcep…

f9922e2

…tion

Less indentation (... but more lines)

56bd63f

Code Style: no blank lines in function bodies

017092d

Remove: Session.run_code_action_async

df4b3fb

Resolve all pending futures at session exit

d0275fa

Print server's partial received bytes (if any) when it unexpectedly s…

43f19ac

…tops

Merge branch 'main' into feat/asyncio

e6ea018

rwols requested a review from rchl September 4, 2026 18:20

rchl reviewed Sep 6, 2026

View reviewed changes

rchl reviewed Sep 7, 2026

View reviewed changes

rwols added 2 commits September 9, 2026 21:28

Address review comments

02af381

Merge branch 'main' into feat/asyncio

13db423

	return cast('ApplyWorkspaceEditResult', {}), cast('WorkspaceEditSummary', {})
	return {"applied": False}, {"created_files": 0, "edited_files": 0, "total_changes": 0}

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