Improve sync.py typing and utilities performance (#390)

asgiref/current_thread_executor.py

@@ -1,6 +1,17 @@
 import queue
+import sys
 import threading
 from concurrent.futures import Executor, Future
+from typing import TYPE_CHECKING, Any, Callable, TypeVar, Union
+
+if sys.version_info >= (3, 10):
+    from typing import ParamSpec
+else:
+    from typing_extensions import ParamSpec
+
+_T = TypeVar("_T")
+_P = ParamSpec("_P")
+_R = TypeVar("_R")
 
 
 class _WorkItem:
@@ -9,13 +20,19 @@ class _WorkItem:
     Copied from ThreadPoolExecutor (but it's private, so we're not going to rely on importing it)
     """
 
-    def __init__(self, future, fn, args, kwargs):
+    def __init__(
+        self,
+        future: "Future[_R]",
+        fn: Callable[_P, _R],
+        *args: _P.args,
+        **kwargs: _P.kwargs,
+    ):
         self.future = future
         self.fn = fn
         self.args = args
         self.kwargs = kwargs
 
-    def run(self):
+    def run(self) -> None:
         __traceback_hide__ = True  # noqa: F841
         if not self.future.set_running_or_notify_cancel():
             return
@@ -24,7 +41,7 @@ def run(self):
         except BaseException as exc:
             self.future.set_exception(exc)
             # Break a reference cycle with the exception 'exc'
-            self = None
+            self = None  # type: ignore[assignment]
         else:
             self.future.set_result(result)
 
@@ -36,12 +53,12 @@ class CurrentThreadExecutor(Executor):
     the thread they came from.
     """
 
-    def __init__(self):
+    def __init__(self) -> None:
         self._work_thread = threading.current_thread()
-        self._work_queue = queue.Queue()
+        self._work_queue: queue.Queue[Union[_WorkItem, "Future[Any]"]] = queue.Queue()
         self._broken = False
 
-    def run_until_future(self, future):
+    def run_until_future(self, future: "Future[Any]") -> None:
         """
         Runs the code in the work queue until a result is available from the future.
         Should be run from the thread the executor is initialised in.
@@ -60,12 +77,18 @@ def run_until_future(self, future):
                 work_item = self._work_queue.get()
                 if work_item is future:
                     return
+                assert isinstance(work_item, _WorkItem)
                 work_item.run()
                 del work_item
         finally:
             self._broken = True
 
-    def submit(self, fn, *args, **kwargs):
+    def _submit(
+        self,
+        fn: Callable[_P, _R],
+        *args: _P.args,
+        **kwargs: _P.kwargs,
+    ) -> "Future[_R]":
         # Check they're not submitting from the same thread
         if threading.current_thread() == self._work_thread:
             raise RuntimeError(
@@ -75,8 +98,18 @@ def submit(self, fn, *args, **kwargs):
         if self._broken:
             raise RuntimeError("CurrentThreadExecutor already quit or is broken")
         # Add to work queue
-        f = Future()
-        work_item = _WorkItem(f, fn, args, kwargs)
+        f: "Future[_R]" = Future()
+        work_item = _WorkItem(f, fn, *args, **kwargs)
         self._work_queue.put(work_item)
         # Return the future
         return f
+
+    # Python 3.9+ has a new signature for submit with a "/" after `fn`, to enforce
+    # it to be a positional argument. If we ignore[override] mypy on 3.9+ will be
+    # happy but 3.7/3.8 will say that the ignore comment is unused, even when
+    # defining them differently based on sys.version_info.
+    # We should be able to remove this when we drop support for 3.7/3.8.
+    if not TYPE_CHECKING:
+
+        def submit(self, fn, *args, **kwargs):
+            return self._submit(fn, *args, **kwargs)