utils/asyn: Replace nest_asyncio with greenback

Fixes #682

devlib/utils/asyn.py

@@ -27,17 +27,7 @@
 import os.path
 import inspect
 
-# 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()
-
+import greenback
 
 def create_task(awaitable, name=None):
     if isinstance(awaitable, asyncio.Task):
@@ -291,13 +281,26 @@ def __set__(self, obj, value):
     def __set_name__(self, owner, name):
         self.name = name
 
-
 def run(coro):
     """
     Similar to :func:`asyncio.run` but can be called while an event loop is
     running.
     """
-    return asyncio.run(coro)
+    try:
+        asyncio.get_running_loop()
+    except RuntimeError:
+        # We are not currently running an event loop, so it's ok to just use
+        # asyncio.run() and let it create one
+        async def f():
+            await greenback.ensure_portal()
+            return await coro
+        return asyncio.run(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
+        return greenback.await_(coro)
 
 
 def asyncf(f):

setup.py

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