3 files changed, 26 insertions, 7 deletions
diff --git a/Lib/asyncio/base_events.py b/Lib/asyncio/base_events.py
index a675fff..9c9d98d 100644
--- a/Lib/asyncio/base_events.py
+++ b/Lib/asyncio/base_events.py
@@ -561,8 +561,13 @@ class BaseEventLoop(events.AbstractEventLoop):
                     'asyncgen': agen
                 })
 
-    async def shutdown_default_executor(self):
-        """Schedule the shutdown of the default executor."""
+    async def shutdown_default_executor(self, timeout=None):
+        """Schedule the shutdown of the default executor.
+
+        The timeout parameter specifies the amount of time the executor will
+        be given to finish joining. The default value is None, which means
+        that the executor will be given an unlimited amount of time.
+        """
         self._executor_shutdown_called = True
         if self._default_executor is None:
             return
@@ -572,7 +577,13 @@ class BaseEventLoop(events.AbstractEventLoop):
         try:
             await future
         finally:
-            thread.join()
+            thread.join(timeout)
+
+        if thread.is_alive():
+            warnings.warn("The executor did not finishing joining "
+                             f"its threads within {timeout} seconds.",
+                             RuntimeWarning, stacklevel=2)
+            self._default_executor.shutdown(wait=False)
 
     def _do_shutdown(self, future):
         try:
diff --git a/Lib/asyncio/constants.py b/Lib/asyncio/constants.py
index f171ead..f0ce043 100644
--- a/Lib/asyncio/constants.py
+++ b/Lib/asyncio/constants.py
@@ -26,6 +26,9 @@ SENDFILE_FALLBACK_READBUFFER_SIZE = 1024 * 256
 FLOW_CONTROL_HIGH_WATER_SSL_READ = 256  # KiB
 FLOW_CONTROL_HIGH_WATER_SSL_WRITE = 512  # KiB
 
+# Default timeout for joining the threads in the threadpool
+THREAD_JOIN_TIMEOUT = 300
+
 # The enum should be here to break circular dependencies between
 # base_events and sslproto
 class _SendfileMode(enum.Enum):
diff --git a/Lib/asyncio/runners.py b/Lib/asyncio/runners.py
index 840b133..b1c4dbd 100644
--- a/Lib/asyncio/runners.py
+++ b/Lib/asyncio/runners.py
@@ -9,7 +9,7 @@ from . import coroutines
 from . import events
 from . import exceptions
 from . import tasks
-
+from . import constants
 
 class _State(enum.Enum):
     CREATED = "created"
@@ -69,7 +69,8 @@ class Runner:
             loop = self._loop
             _cancel_all_tasks(loop)
             loop.run_until_complete(loop.shutdown_asyncgens())
-            loop.run_until_complete(loop.shutdown_default_executor())
+            loop.run_until_complete(
+                loop.shutdown_default_executor(constants.THREAD_JOIN_TIMEOUT))
         finally:
             if self._set_event_loop:
                 events.set_event_loop(None)
@@ -160,8 +161,8 @@ def run(main, *, debug=None):
     """Execute the coroutine and return the result.
 
     This function runs the passed coroutine, taking care of
-    managing the asyncio event loop and finalizing asynchronous
-    generators.
+    managing the asyncio event loop, finalizing asynchronous
+    generators and closing the default executor.
 
     This function cannot be called when another asyncio event loop is
     running in the same thread.
@@ -172,6 +173,10 @@ def run(main, *, debug=None):
     It should be used as a main entry point for asyncio programs, and should
     ideally only be called once.
 
+    The executor is given a timeout duration of 5 minutes to shutdown.
+    If the executor hasn't finished within that duration, a warning is
+    emitted and the executor is closed.
+
     Example:
 
         async def main():