backward compatibility with Python <=3.10

Signed-off-by: Achille Roussel <achille.roussel@gmail.com>

Author: achille-roussel

src/dispatch/asyncio.py

@@ -0,0 +1,105 @@
+import asyncio
+import functools
+import inspect
+import signal
+import threading
+
+class Runner:
+    """Runner is a class similar to asyncio.Runner but that we use for backward
+    compatibility with Python 3.10 and earlier.
+    """
+
+    def __init__(self):
+        self._loop = asyncio.new_event_loop()
+        self._interrupt_count = 0
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, *args, **kwargs):
+        self.close()
+
+    def close(self):
+        try:
+            loop = self._loop
+            _cancel_all_tasks(loop)
+            loop.run_until_complete(loop.shutdown_asyncgens())
+            if hasattr(loop, 'shutdown_default_executor'): # Python 3.9+
+                loop.run_until_complete(loop.shutdown_default_executor())
+        finally:
+            loop.close()
+
+    def get_loop(self):
+        return self._loop
+
+    def run(self, coro):
+        if not inspect.iscoroutine(coro):
+            raise ValueError("a coroutine was expected, got {!r}".format(coro))
+
+        try:
+            asyncio.get_running_loop()
+        except RuntimeError:
+            pass
+        else:
+            raise RuntimeError("Runner.run() cannot be called from a running event loop")
+
+        task = self._loop.create_task(coro)
+        sigint_handler = None
+
+        if (threading.current_thread() is threading.main_thread()
+            and signal.getsignal(signal.SIGINT) is signal.default_int_handler
+        ):
+            sigint_handler = functools.partial(self._on_sigint, main_task=task)
+            try:
+                signal.signal(signal.SIGINT, sigint_handler)
+            except ValueError:
+                # `signal.signal` may throw if `threading.main_thread` does
+                # not support signals (e.g. embedded interpreter with signals
+                # not registered - see gh-91880)
+                sigint_handler = None
+
+        self._interrupt_count = 0
+        try:
+            asyncio.set_event_loop(self._loop)
+            return self._loop.run_until_complete(task)
+        except asyncio.CancelledError:
+            if self._interrupt_count > 0:
+                uncancel = getattr(task, "uncancel", None)
+                if uncancel is not None and uncancel() == 0:
+                    raise KeyboardInterrupt()
+            raise  # CancelledError
+        finally:
+            asyncio.set_event_loop(None)
+            if (sigint_handler is not None
+                and signal.getsignal(signal.SIGINT) is sigint_handler
+            ):
+                signal.signal(signal.SIGINT, signal.default_int_handler)
+
+    def _on_sigint(self, signum, frame, main_task):
+        self._interrupt_count += 1
+        if self._interrupt_count == 1 and not main_task.done():
+            main_task.cancel()
+            # wakeup loop if it is blocked by select() with long timeout
+            self._loop.call_soon_threadsafe(lambda: None)
+            return
+        raise KeyboardInterrupt()
+
+def _cancel_all_tasks(loop):
+    to_cancel = asyncio.all_tasks(loop)
+    if not to_cancel:
+        return
+
+    for task in to_cancel:
+        task.cancel()
+
+    loop.run_until_complete(asyncio.gather(*to_cancel, return_exceptions=True))
+
+    for task in to_cancel:
+        if task.cancelled():
+            continue
+        if task.exception() is not None:
+            loop.call_exception_handler({
+                'message': 'unhandled exception during asyncio.run() shutdown',
+                'exception': task.exception(),
+                'task': task,
+            })

src/dispatch/experimental/lambda_handler.py

@@ -26,6 +26,7 @@ def handler(event, context):
 
 from awslambdaric.lambda_context import LambdaContext
 
+from dispatch.asyncio import Runner
 from dispatch.function import Registry
 from dispatch.proto import Input
 from dispatch.sdk.v1 import function_pb2 as function_pb
@@ -93,7 +94,7 @@ def handle(
 
         input = Input(req)
         try:
-            with asyncio.Runner() as runner:
+            with Runner() as runner:
                 output = runner.run(func._primitive_call(input))
         except Exception:
             logger.error("function '%s' fatal error", req.function, exc_info=True)

src/dispatch/flask.py

@@ -23,6 +23,7 @@ def read_root():
 
 from flask import Flask, make_response, request
 
+from dispatch.asyncio import Runner
 from dispatch.function import Registry
 from dispatch.http import FunctionServiceError, function_service_run
 from dispatch.signature import Ed25519PublicKey, parse_verification_key
@@ -90,7 +91,7 @@ def _handle_error(self, exc: FunctionServiceError):
     def _execute(self):
         data: bytes = request.get_data(cache=False)
 
-        with asyncio.Runner() as runner:
+        with Runner() as runner:
             content = runner.run(
                 function_service_run(
                     request.url,

src/dispatch/http.py

@@ -9,6 +9,7 @@
 
 from http_message_signatures import InvalidSignature
 
+from dispatch.asyncio import Runner
 from dispatch.function import Registry
 from dispatch.proto import Input
 from dispatch.sdk.v1 import function_pb2 as function_pb
@@ -121,7 +122,7 @@ def do_POST(self):
         url = self.requestline  # TODO: need full URL
 
         try:
-            with asyncio.Runner() as runner:
+            with Runner() as runner:
                 content = runner.run(
                     function_service_run(
                         url,

tests/dispatch/test_scheduler.py

@@ -1,7 +1,7 @@
-import asyncio
 import unittest
 from typing import Any, Callable, List, Optional, Set, Type
 
+from dispatch.asyncio import Runner
 from dispatch.coroutine import AnyException, any, call, gather, race
 from dispatch.experimental.durable import durable
 from dispatch.proto import Arguments, Call, CallResult, Error, Input, Output, TailCall
@@ -55,7 +55,7 @@ async def raises_error():
 
 class TestOneShotScheduler(unittest.TestCase):
     def setUp(self):
-        self.runner = asyncio.Runner()
+        self.runner = Runner()
 
     def tearDown(self):
         self.runner.close()