Revert "utils/asyn: Replace nest_asyncio with greenback"

This reverts commit 83d3568.

devlib/utils/asyn.py

@@ -26,43 +26,17 @@
 import pathlib
 import os.path
 import inspect
-import threading
 
-import greenback
-
-
-def _wrap_coro(coro):
-    async def coro_f():
-        await greenback.ensure_portal()
-        return await coro
-    return coro_f()
-
-
-class _GreenbackEventLoop(asyncio.AbstractEventLoop):
-    def __init__(self, loop):
-        self.__loop = loop
-
-    # Because AbstractEventLoop has default implementation for every method, we
-    # cannot just use __getattr__, otherwise we will hit these default
-    # implementation first.
-    def __getattribute__(self, attr):
-        if attr == '_GreenbackEventLoop__loop':
-            return object.__getattribute__(self, '_GreenbackEventLoop__loop')
-        else:
-            try:
-                override = type(self)._OVERRIDES[attr]
-            except KeyError:
-                return getattr(self.__loop, attr)
-            else:
-                return override.__get__(self, type(self))
-
-    def create_task(self, coro, *args, **kwargs):
-        loop = self.__loop
-        return loop.create_task(_wrap_coro(coro), *args, **kwargs)
-
-    _OVERRIDES = dict(
-        create_task=create_task,
-    )
+# Allow nesting asyncio loops, which is necessary for:
+# * Being able to call the blocking variant of a function from an async
+#   function for backward compat
+# * Critically, run the blocking variant of a function in a Jupyter notebook
+#   environment, since it also uses asyncio.
+#
+# Maybe there is still hope for future versions of Python though:
+# https://bugs.python.org/issue22239
+import nest_asyncio
+nest_asyncio.apply()
 
 
 def create_task(awaitable, name=None):
@@ -318,58 +292,12 @@ def __set_name__(self, owner, name):
         self.name = name
 
 
-# This thread runs an event loop that guarantees having greenback portals
-# installed for each task that is created. This can otherwise not be
-# guaranteed, even with import-time manipulations as the import itself might
-# happen in an already-created tasks, e.g. inside Jupyter lab notebooks.
-_LOOP = None
-_LOOP_READY = threading.Event()
-
-def _coro_runner():
-    global _LOOP
-    loop = asyncio.new_event_loop()
-    loop = _GreenbackEventLoop(loop)
-    asyncio.set_event_loop(loop)
-
-    _LOOP = loop
-    _LOOP_READY.set()
-    _LOOP.run_forever()
-
-_RUN_THREAD = threading.Thread(target=_coro_runner, daemon=True)
-_RUN_THREAD.start()
-
-
 def run(coro):
     """
     Similar to :func:`asyncio.run` but can be called while an event loop is
     running.
     """
-    try:
-        asyncio.get_running_loop()
-    except RuntimeError:
-        async def coro_f():
-            return await coro
-
-        # We are not currently running an event loop, so it's ok to just use
-        # asyncio.run() and let it create one
-        return asyncio.run(
-            # Create a portal, so that nested calls to run() can cross async
-            # boundaries
-            greenback.with_portal_run(coro_f)
-        )
-    else:
-        # We are currently running an event loop, so we need greenback to
-        # re-enter the event loop, as this is not supported in the standard
-        # library:
-        # https://github.com/python/cpython/issues/66435
-        if greenback.has_portal():
-            return greenback.await_(coro)
-        else:
-            # If we don't have a portal setup for the current task, run the
-            # coroutine on the dedicated thread that has a policy which
-            # installs portals for every new task.
-            _LOOP_READY.wait()
-            return asyncio.run_coroutine_threadsafe(coro, _LOOP).result()
+    return asyncio.run(coro)
 
 
 def asyncf(f):

setup.py

@@ -104,7 +104,7 @@ def _load_path(filepath):
         'pandas',
         'pytest',
         'lxml', # More robust xml parsing
-        'greenback', # Allows running nested asyncio loops
+        'nest_asyncio', # Allows running nested asyncio loops
         'future', # for the "past" Python package
         'ruamel.yaml >= 0.15.72', # YAML formatted config parsing
     ],