handle closed event loop in async script magics

leave other problems with asyncio implementation for another PR

IPython/core/magics/script.py

@@ -1,357 +1,375 b''
 """Magic functions for running cells in various scripts."""
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
 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 traitlets import Dict, List, default
 
 from IPython.core import magic_arguments
 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
 
 #-----------------------------------------------------------------------------
 # Magic implementation classes
 #-----------------------------------------------------------------------------
 
 def script_args(f):
     """single decorator for adding script args"""
     args = [
         magic_arguments.argument(
             '--out', type=str,
             help="""The variable in which to store stdout from the script.
             If the script is backgrounded, this will be the stdout *pipe*,
             instead of the stderr text itself and will not be auto closed.
             """
         ),
         magic_arguments.argument(
             '--err', type=str,
             help="""The variable in which to store stderr from the script.
             If the script is backgrounded, this will be the stderr *pipe*,
             instead of the stderr text itself and will not be autoclosed.
             """
         ),
         magic_arguments.argument(
             '--bg', action="store_true",
             help="""Whether to run the script in the background.
             If given, the only way to see the output of the command is
             with --out/err.
             """
         ),
         magic_arguments.argument(
             '--proc', type=str,
             help="""The variable in which to store Popen instance.
             This is used only when --bg option is given.
             """
         ),
         magic_arguments.argument(
             '--no-raise-error', action="store_false", dest='raise_error',
             help="""Whether you should raise an error message in addition to 
             a stream on stderr if you get a nonzero exit code.
             """
         )
     ]
     for arg in args:
         f = arg(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
 
-    loop = policy.get_event_loop()
+    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
     
     This defines a base `%%script` cell magic for running a cell
     with a program in a subprocess, and registers a few top-level
     magics that call %%script with common interpreters.
     """
     script_magics = List(
         help="""Extra script cell magics to define
         
         This generates simple wrappers of `%%script foo` as `%%foo`.
         
         If you want to add script magics that aren't on your path,
         specify them in script_paths
         """,
     ).tag(config=True)
     @default('script_magics')
     def _script_magics_default(self):
         """default to a common list of programs"""
         
         defaults = [
             'sh',
             'bash',
             'perl',
             'ruby',
             'python',
             'python2',
             'python3',
             'pypy',
         ]
         if os.name == 'nt':
             defaults.extend([
                 'cmd',
             ])
         
         return defaults
     
     script_paths = Dict(
         help="""Dict mapping short 'ruby' names to full paths, such as '/opt/secret/bin/ruby'
         
         Only necessary for items in script_magics where the default path will not
         find the right interpreter.
         """
     ).tag(config=True)
     
     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)
 
     def __del__(self):
         self.kill_bg_processes()
     
     def _generate_script_magics(self):
         cell_magics = self.magics['cell']
         for name in self.script_magics:
             cell_magics[name] = self._make_script_magic(name)
     
     def _make_script_magic(self, name):
         """make a named magic, that calls %%script with a particular program"""
         # expand to explicit path if necessary:
         script = self.script_paths.get(name, name)
         
         @magic_arguments.magic_arguments()
         @script_args
         def named_script_magic(line, cell):
             # if line, add it as cl-flags
             if line:
                 line = "%s %s" % (script, line)
             else:
                 line = script
             return self.shebang(line, cell)
         
         # write a basic docstring:
         named_script_magic.__doc__ = \
         """%%{name} script magic
         
         Run cells with {script} in a subprocess.
         
         This is a shortcut for `%%script {script}`
         """.format(**locals())
         
         return named_script_magic
     
     @magic_arguments.magic_arguments()
     @script_args
     @cell_magic("script")
     @dec_safe_watcher
     def shebang(self, line, cell):
         """Run a cell via a shell command
         
         The `%%script` line is like the #! line of script,
         specifying a program (bash, perl, ruby, etc.) with which to run.
         
         The rest of the cell is run by that program.
         
         Examples
         --------
         ::
         
             In [1]: %%script bash
                ...: for i in 1 2 3; do
                ...:   echo $i
                ...: done
             1
             2
             3
         """
 
         async def _handle_stream(stream, stream_arg, file_object):
             while True:
                 line = (await stream.readline()).decode("utf8")
                 if not line:
                     break
                 if stream_arg:
                     self.shell.user_ns[stream_arg] = line
                 else:
                     file_object.write(line)
                     file_object.flush()
 
         async def _stream_communicate(process, cell):
             process.stdin.write(cell)
             process.stdin.close()
             stdout_task = asyncio.create_task(
                 _handle_stream(process.stdout, args.out, sys.stdout)
             )
             stderr_task = asyncio.create_task(
                 _handle_stream(process.stderr, args.err, sys.stderr)
             )
             await asyncio.wait([stdout_task, stderr_task])
             await process.wait()
 
-        if sys.platform.startswith("win"):
-            asyncio.set_event_loop_policy(asyncio.WindowsProactorEventLoopPolicy())
-        loop = asyncio.get_event_loop_policy().get_event_loop()
+        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(
                 asyncio.create_subprocess_exec(
                     *cmd,
                     stdout=asyncio.subprocess.PIPE,
                     stderr=asyncio.subprocess.PIPE,
                     stdin=asyncio.subprocess.PIPE,
                 )
             )
         except OSError as e:
             if e.errno == errno.ENOENT:
                 print("Couldn't find program: %r" % cmd[0])
                 return
             else:
                 raise
         
         if not cell.endswith('\n'):
             cell += '\n'
         cell = cell.encode('utf8', 'replace')
         if args.bg:
             self.bg_processes.append(p)
             self._gc_bg_processes()
             to_close = []
             if args.out:
                 self.shell.user_ns[args.out] = p.stdout
             else:
                 to_close.append(p.stdout)
             if args.err:
                 self.shell.user_ns[args.err] = p.stderr
             else:
                 to_close.append(p.stderr)
             self.job_manager.new(self._run_script, p, cell, to_close, daemon=True)
             if args.proc:
                 self.shell.user_ns[args.proc] = p
             return
         
         try:
             loop.run_until_complete(_stream_communicate(p, cell))
         except KeyboardInterrupt:
             try:
                 p.send_signal(signal.SIGINT)
                 time.sleep(0.1)
                 if p.returncode is not None:
                     print("Process is interrupted.")
                     return
                 p.terminate()
                 time.sleep(0.1)
                 if p.returncode is not None:
                     print("Process is terminated.")
                     return
                 p.kill()
                 print("Process is killed.")
             except OSError:
                 pass
             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,
             # in case it's stuck in uninterruptible sleep. -9 = SIGKILL
             rc = p.returncode or -9
             raise CalledProcessError(rc, cell)
 
     shebang.__skip_doctest__ = os.name != "posix"
     
     def _run_script(self, p, cell, to_close):
         """callback for running the script in the background"""
         p.stdin.write(cell)
         p.stdin.close()
         for s in to_close:
             s.close()
         p.wait()
 
     @line_magic("killbgscripts")
     def killbgscripts(self, _nouse_=''):
         """Kill all BG processes started by %%script and its family."""
         self.kill_bg_processes()
         print("All background processes were killed.")
 
     def kill_bg_processes(self):
         """Kill all BG processes which are still running."""
         if not self.bg_processes:
             return
         for p in self.bg_processes:
             if p.returncode is None:
                 try:
                     p.send_signal(signal.SIGINT)
                 except:
                     pass
         time.sleep(0.1)
         self._gc_bg_processes()
         if not self.bg_processes:
             return
         for p in self.bg_processes:
             if p.returncode is None:
                 try:
                     p.terminate()
                 except:
                     pass
         time.sleep(0.1)
         self._gc_bg_processes()
         if not self.bg_processes:
             return
         for p in self.bg_processes:
             if p.returncode is None:
                 try:
                     p.kill()
                 except:
                     pass
         self._gc_bg_processes()
 
     def _gc_bg_processes(self):
         self.bg_processes = [p for p in self.bg_processes if p.returncode is None]