Use lock to make sure target started

Author: iaalm

Lib/test/test_asyncio/test_tasks.py

@@ -8,6 +8,7 @@
 import random
 import re
 import sys
+from threading import Event
 import traceback
 import types
 import unittest
@@ -3681,15 +3682,21 @@ def task_factory(loop, coro):
         self.assertEqual(context['exception'], exc_context.exception)
 
     def test_run_coroutine_threadsafe_and_cancel(self):
-        async def target():
-            thread_future = asyncio.run_coroutine_threadsafe(self.add(1, 2), self.loop)
-            await asyncio.sleep(0)
+        target_started = Event()
+        async def _target():
+            target_started.set()
+            await asyncio.sleep(0.1)
+            return 1
 
+        def _in_thread():
+            thread_future = asyncio.run_coroutine_threadsafe(_target(), self.loop)
+            # wait target started then cancel
+            target_started.wait()
             thread_future.cancel()
-            await asyncio.sleep(0)
+        _ = self.loop.run_in_executor(None, _in_thread)
 
-        future = self.loop.run_in_executor(None, target)
-        self.loop.run_until_complete(future)
+        # start main loop to do things
+        self.loop.run_until_complete(asyncio.sleep(0.05))
         self.assertEqual(0, len(self.loop._ready))