avoid deprecated get_event_loop

use our own `async_helpers.get_asyncio_loop` to track the global event loop

script magics use dedicated background asyncio loop
instead of trying to work on the main loop, which may or may not exist

_AsyncIOProxy wraps background script objects to transfer awaitables across loops

only works for coroutine methods, which might be good enough? Works for read, etc.

IPython/core/async_helpers.py

@@ -14,26 +14,46 b' Python semantics.'
 import ast
 import asyncio
 import inspect
+from functools import wraps
 
+_asyncio_event_loop = None
 
-class _AsyncIORunner:
-    def __init__(self):
-        self._loop = None
-
-    @property
-    def loop(self):
-        """Always returns a non-closed event loop"""
-        if self._loop is None or self._loop.is_closed():
-            policy = asyncio.get_event_loop_policy()
-            self._loop = policy.new_event_loop()
-            policy.set_event_loop(self._loop)
-        return self._loop
 
+def get_asyncio_loop():
+    """asyncio has deprecated get_event_loop
+
+    Replicate it here, with our desired semantics:
+
+    - always returns a valid, not-closed loop
+    - not thread-local like asyncio's,
+      because we only want one loop for IPython
+    - if called from inside a coroutine (e.g. in ipykernel),
+      return the running loop
+
+    .. versionadded:: 8.0
+    """
+    try:
+        return asyncio.get_running_loop()
+    except RuntimeError:
+        # not inside a coroutine,
+        # track our own global
+        pass
+
+    # not thread-local like asyncio's,
+    # because we only track one event loop to run for IPython itself,
+    # always in the main thread.
+    global _asyncio_event_loop
+    if _asyncio_event_loop is None or _asyncio_event_loop.is_closed():
+        _asyncio_event_loop = asyncio.new_event_loop()
+    return _asyncio_event_loop
+
+
+class _AsyncIORunner:
     def __call__(self, coro):
         """
         Handler for asyncio autoawait
         """
-        return self.loop.run_until_complete(coro)
+        return get_asyncio_loop().run_until_complete(coro)
 
     def __str__(self):
         return "asyncio"
@@ -42,6 +62,39 b' class _AsyncIORunner:'
 _asyncio_runner = _AsyncIORunner()
 
 
+class _AsyncIOProxy:
+    """Proxy-object for an asyncio
+
+    Any coroutine methods will be wrapped in event_loop.run_
+    """
+
+    def __init__(self, obj, event_loop):
+        self._obj = obj
+        self._event_loop = event_loop
+
+    def __repr__(self):
+        return f"<_AsyncIOProxy({self._obj!r})>"
+
+    def __getattr__(self, key):
+        attr = getattr(self._obj, key)
+        if inspect.iscoroutinefunction(attr):
+            # if it's a coroutine method,
+            # return a threadsafe wrapper onto the _current_ asyncio loop
+            @wraps(attr)
+            def _wrapped(*args, **kwargs):
+                concurrent_future = asyncio.run_coroutine_threadsafe(
+                    attr(*args, **kwargs), self._event_loop
+                )
+                return asyncio.wrap_future(concurrent_future)
+
+            return _wrapped
+        else:
+            return attr
+
+    def __dir__(self):
+        return dir(self._obj)
+
+
 def _curio_runner(coroutine):
     """
     handler for curio autoawait

IPython/core/magics/script.py

@@ -6,19 +6,18 b''
 import asyncio
 import atexit
 import errno
-import functools
 import os
 import signal
 import sys
 import time
-from contextlib import contextmanager
 from subprocess import CalledProcessError
+from threading import Thread
 
-from traitlets import Dict, List, default
+from traitlets import Any, Dict, List, default
 
 from IPython.core import magic_arguments
+from IPython.core.async_helpers import _AsyncIOProxy
 from IPython.core.magic import Magics, cell_magic, line_magic, magics_class
-from IPython.lib.backgroundjobs import BackgroundJobManager
 from IPython.utils.process import arg_split
 
 #-----------------------------------------------------------------------------
@@ -67,48 +66,6 b' def script_args(f):'
     return f
 
 
-@contextmanager
-def safe_watcher():
-    if sys.platform == "win32":
-        yield
-        return
-
-    from asyncio import SafeChildWatcher
-
-    policy = asyncio.get_event_loop_policy()
-    old_watcher = policy.get_child_watcher()
-    if isinstance(old_watcher, SafeChildWatcher):
-        yield
-        return
-
-    try:
-        loop = policy.get_event_loop()
-        if loop.is_closed():
-            raise RuntimeError("open a new one")
-    except RuntimeError:
-        # closed loop, make a new one
-        loop = policy.new_event_loop()
-        policy.set_event_loop(loop)
-
-    try:
-        watcher = asyncio.SafeChildWatcher()
-        watcher.attach_loop(loop)
-        policy.set_child_watcher(watcher)
-        yield
-    finally:
-        watcher.close()
-        policy.set_child_watcher(old_watcher)
-
-
-def dec_safe_watcher(fun):
-    @functools.wraps(fun)
-    def _inner(*args, **kwargs):
-        with safe_watcher():
-            return fun(*args, **kwargs)
-
-    return _inner
-
-
 @magics_class
 class ScriptMagics(Magics):
     """Magics for talking to scripts
@@ -117,6 +74,17 b' class ScriptMagics(Magics):'
     with a program in a subprocess, and registers a few top-level
     magics that call %%script with common interpreters.
     """
+
+    event_loop = Any(
+        help="""
+        The event loop on which to run subprocesses
+
+        Not the main event loop,
+        because we want to be able to make blocking calls
+        and have certain requirements we don't want to impose on the main loop.
+        """
+    )
+
     script_magics = List(
         help="""Extra script cell magics to define
         
@@ -158,7 +126,6 b' class ScriptMagics(Magics):'
     def __init__(self, shell=None):
         super(ScriptMagics, self).__init__(shell=shell)
         self._generate_script_magics()
-        self.job_manager = BackgroundJobManager()
         self.bg_processes = []
         atexit.register(self.kill_bg_processes)
 
@@ -199,7 +166,6 b' class ScriptMagics(Magics):'
     @magic_arguments.magic_arguments()
     @script_args
     @cell_magic("script")
-    @dec_safe_watcher
     def shebang(self, line, cell):
         """Run a cell via a shell command
 
@@ -221,6 +187,27 b' class ScriptMagics(Magics):'
             3
         """
 
+        # Create the event loop in which to run script magics
+        # this operates on a background thread
+        if self.event_loop is None:
+            if sys.platform == "win32":
+                # don't override the current policy,
+                # just create an event loop
+                event_loop = asyncio.WindowsProactorEventLoopPolicy().new_event_loop()
+            else:
+                event_loop = asyncio.new_event_loop()
+            self.event_loop = event_loop
+
+            # start the loop in a background thread
+            asyncio_thread = Thread(target=event_loop.run_forever, daemon=True)
+            asyncio_thread.start()
+        else:
+            event_loop = self.event_loop
+
+        def in_thread(coro):
+            """Call a coroutine on the asyncio thread"""
+            return asyncio.run_coroutine_threadsafe(coro, event_loop).result()
+
         async def _handle_stream(stream, stream_arg, file_object):
             while True:
                 line = (await stream.readline()).decode("utf8")
@@ -244,23 +231,11 b' class ScriptMagics(Magics):'
             await asyncio.wait([stdout_task, stderr_task])
             await process.wait()
 
-        policy = asyncio.get_event_loop_policy()
-        if sys.platform.startswith("win") and not isinstance(
-            policy, asyncio.WindowsProactorEventLoopPolicy
-        ):
-            # _do not_ overwrite the current policy
-            policy = asyncio.WindowsProactorEventLoopPolicy()
-
-        try:
-            loop = policy.get_event_loop()
-        except RuntimeError:
-            # closed loop, make a new one
-            loop = policy.new_event_loop()
-            policy.set_event_loop(loop)
         argv = arg_split(line, posix=not sys.platform.startswith("win"))
         args, cmd = self.shebang.parser.parse_known_args(argv)
+
         try:
-            p = loop.run_until_complete(
+            p = in_thread(
                 asyncio.create_subprocess_exec(
                     *cmd,
                     stdout=asyncio.subprocess.PIPE,
@@ -283,29 +258,34 b' class ScriptMagics(Magics):'
             self._gc_bg_processes()
             to_close = []
             if args.out:
-                self.shell.user_ns[args.out] = p.stdout
+                self.shell.user_ns[args.out] = _AsyncIOProxy(p.stdout, event_loop)
             else:
                 to_close.append(p.stdout)
             if args.err:
-                self.shell.user_ns[args.err] = p.stderr
+                self.shell.user_ns[args.err] = _AsyncIOProxy(p.stderr, event_loop)
             else:
                 to_close.append(p.stderr)
-            self.job_manager.new(self._run_script, p, cell, to_close, daemon=True)
+            event_loop.call_soon_threadsafe(
+                lambda: asyncio.Task(self._run_script(p, cell, to_close))
+            )
             if args.proc:
-                self.shell.user_ns[args.proc] = p
+                proc_proxy = _AsyncIOProxy(p, event_loop)
+                proc_proxy.stdout = _AsyncIOProxy(p.stdout, event_loop)
+                proc_proxy.stderr = _AsyncIOProxy(p.stderr, event_loop)
+                self.shell.user_ns[args.proc] = proc_proxy
             return
         
         try:
-            loop.run_until_complete(_stream_communicate(p, cell))
+            in_thread(_stream_communicate(p, cell))
         except KeyboardInterrupt:
             try:
                 p.send_signal(signal.SIGINT)
-                time.sleep(0.1)
+                in_thread(asyncio.wait_for(p.wait(), timeout=0.1))
                 if p.returncode is not None:
                     print("Process is interrupted.")
                     return
                 p.terminate()
-                time.sleep(0.1)
+                in_thread(asyncio.wait_for(p.wait(), timeout=0.1))
                 if p.returncode is not None:
                     print("Process is terminated.")
                     return
@@ -316,6 +296,7 b' class ScriptMagics(Magics):'
             except Exception as e:
                 print("Error while terminating subprocess (pid=%i): %s" % (p.pid, e))
             return
+
         if args.raise_error and p.returncode!=0:
             # If we get here and p.returncode is still None, we must have
             # killed it but not yet seen its return code. We don't wait for it,
@@ -325,13 +306,19 b' class ScriptMagics(Magics):'
 
     shebang.__skip_doctest__ = os.name != "posix"
     
-    def _run_script(self, p, cell, to_close):
+    async def _run_script(self, p, cell, to_close):
         """callback for running the script in the background"""
+
         p.stdin.write(cell)
+        await p.stdin.drain()
         p.stdin.close()
+        await p.stdin.wait_closed()
+        await p.wait()
+        # asyncio read pipes have no close
+        # but we should drain the data anyway
         for s in to_close:
-            s.close()
-        p.wait()
+            await s.read()
+        self._gc_bg_processes()
 
     @line_magic("killbgscripts")
     def killbgscripts(self, _nouse_=''):

IPython/core/tests/test_interactiveshell.py

@@ -1049,10 +1049,10 b' def test_custom_exc_count():'
 
 
 def test_run_cell_async():
-    loop = asyncio.get_event_loop_policy().get_event_loop()
     ip.run_cell("import asyncio")
     coro = ip.run_cell_async("await asyncio.sleep(0.01)\n5")
     assert asyncio.iscoroutine(coro)
+    loop = asyncio.new_event_loop()
     result = loop.run_until_complete(coro)
     assert isinstance(result, interactiveshell.ExecutionResult)
     assert result.result == 5

IPython/core/tests/test_magic.py

@@ -988,7 +988,7 b' def test_script_out(event_loop):'
 
     ip = get_ipython()
     ip.run_cell_magic("script", "--out output sh", "echo 'hi'")
-    assert event_loop.is_running() is False
+    assert not event_loop.is_running()
     assert ip.user_ns["output"] == "hi\n"
 
 
@@ -998,9 +998,9 b' def test_script_out(event_loop):'
 )
 def test_script_err(event_loop):
     ip = get_ipython()
-    assert event_loop.is_running() is False
+    assert not event_loop.is_running()
     ip.run_cell_magic("script", "--err error sh", "echo 'hello' >&2")
-    assert event_loop.is_running() is False
+    assert not event_loop.is_running()
     assert ip.user_ns["error"] == "hello\n"
 
 
@@ -1022,13 +1022,11 b' def test_script_out_err():'
 @pytest.mark.skipif(
     sys.platform == "win32", reason="This test does not run under Windows"
 )
-async def test_script_bg_out(event_loop):
+async def test_script_bg_out():
     ip = get_ipython()
     ip.run_cell_magic("script", "--bg --out output sh", "echo 'hi'")
     assert (await ip.user_ns["output"].read()) == b"hi\n"
-    ip.user_ns["output"].close()
-    event_loop.stop()
-
+    assert ip.user_ns["output"].at_eof()
 
 @dec.skip_win32
 @pytest.mark.skipif(
@@ -1038,7 +1036,7 b' async def test_script_bg_err():'
     ip = get_ipython()
     ip.run_cell_magic("script", "--bg --err error sh", "echo 'hello' >&2")
     assert (await ip.user_ns["error"].read()) == b"hello\n"
-    ip.user_ns["error"].close()
+    assert ip.user_ns["error"].at_eof()
 
 
 @dec.skip_win32
@@ -1052,8 +1050,27 b' async def test_script_bg_out_err():'
     )
     assert (await ip.user_ns["output"].read()) == b"hi\n"
     assert (await ip.user_ns["error"].read()) == b"hello\n"
-    ip.user_ns["output"].close()
-    ip.user_ns["error"].close()
+    assert ip.user_ns["output"].at_eof()
+    assert ip.user_ns["error"].at_eof()
+
+
[e-mail]_win32
[e-mail](
+    sys.platform == "win32", reason="This test does not run under Windows"
+)
+async def test_script_bg_proc():
+    ip = get_ipython()
+    ip.run_cell_magic(
+        "script", "--bg --proc p sh --out out", "echo 'hi'\necho 'hello' >&2"
+    )
+    p = ip.user_ns["p"]
+    await p.wait()
+    assert p.returncode == 0
+    assert (await p.stdout.read()) == b"hi\n"
+    # not captured, so empty
+    assert (await p.stderr.read()) == b""
+    assert p.stdout.at_eof()
+    assert p.stderr.at_eof()
 
 
 def test_script_defaults():

IPython/terminal/interactiveshell.py

@@ -6,6 +6,7 b' import sys'
 import warnings
 from warnings import warn
 
+from IPython.core.async_helpers import get_asyncio_loop
 from IPython.core.interactiveshell import InteractiveShell, InteractiveShellABC
 from IPython.utils import io
 from IPython.utils.py3compat import input
@@ -521,13 +522,13 b' class TerminalInteractiveShell(InteractiveShell):'
         # while/true inside which will freeze the prompt.
 
         policy = asyncio.get_event_loop_policy()
-        try:
-            old_loop = policy.get_event_loop()
-        except RuntimeError:
-            # This happens when the the event loop is closed,
-            # e.g. by calling `asyncio.run()`.
-            old_loop = None
+        old_loop = get_asyncio_loop()
 
+        # FIXME: prompt_toolkit is using the deprecated `asyncio.get_event_loop`
+        # to get the current event loop.
+        # This will probably be replaced by an attribute or input argument,
+        # at which point we can stop calling the soon-to-be-deprecated `set_event_loop` here.
+        if old_loop is not self.pt_loop:
         policy.set_event_loop(self.pt_loop)
         try:
             with patch_stdout(raw=True):
@@ -536,7 +537,7 b' class TerminalInteractiveShell(InteractiveShell):'
                     **self._extra_prompt_options())
         finally:
             # Restore the original event loop.
-            if old_loop is not None:
+            if old_loop is not None and old_loop is not self.pt_loop:
                 policy.set_event_loop(old_loop)
 
         return text
@@ -652,7 +653,7 b' class TerminalInteractiveShell(InteractiveShell):'
                 # When we integrate the asyncio event loop, run the UI in the
                 # same event loop as the rest of the code. don't use an actual
                 # input hook. (Asyncio is not made for nesting event loops.)
-                self.pt_loop = asyncio.get_event_loop_policy().get_event_loop()
+                self.pt_loop = get_asyncio_loop()
 
             elif self._inputhook:
                 # If an inputhook was set, create a new asyncio event loop with

IPython/terminal/pt_inputhooks/asyncio.py

@@ -27,15 +27,12 b' prompt_toolkit`s `patch_stdout`)::'
     In [4]: asyncio.ensure_future(f())
 
 """
-import asyncio
 from prompt_toolkit import __version__ as ptk_version
 
-PTK3 = ptk_version.startswith('3.')
+from IPython.core.async_helpers import get_asyncio_loop
 
+PTK3 = ptk_version.startswith('3.')
 
-# Keep reference to the original asyncio loop, because getting the event loop
-# within the input hook would return the other loop.
-loop = asyncio.get_event_loop_policy().get_event_loop()
 
 
 def inputhook(context):
@@ -52,6 +49,9 b' def inputhook(context):'
     # For prompt_toolkit 2.0, we can run the current asyncio event loop,
     # because prompt_toolkit 2.0 uses a different event loop internally.
 
+    # get the persistent asyncio event loop
+    loop = get_asyncio_loop()
+
     def stop():
         loop.stop()
 
@@ -61,4 +61,3 b' def inputhook(context):'
         loop.run_forever()
     finally:
         loop.remove_reader(fileno)
-