Pass Windows interrupt event to kernels as an environment variable

This allows third party kernels to use our interrupt mechanism on
Windows.

Closes gh-5840

IPython/kernel/launcher.py

@@ -1,256 +1,261 b''
 """Utilities for launching kernels
 """
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
 import os
 import sys
 from subprocess import Popen, PIPE
 
 from IPython.utils.encoding import getdefaultencoding
 from IPython.utils.py3compat import cast_bytes_py2
 
 
 def swallow_argv(argv, aliases=None, flags=None):
     """strip frontend-specific aliases and flags from an argument list
     
     For use primarily in frontend apps that want to pass a subset of command-line
     arguments through to a subprocess, where frontend-specific flags and aliases
     should be removed from the list.
     
     Parameters
     ----------
     
     argv : list(str)
         The starting argv, to be filtered
     aliases : container of aliases (dict, list, set, etc.)
         The frontend-specific aliases to be removed
     flags : container of flags (dict, list, set, etc.)
         The frontend-specific flags to be removed
     
     Returns
     -------
     
     argv : list(str)
         The argv list, excluding flags and aliases that have been stripped
     """
     
     if aliases is None:
         aliases = set()
     if flags is None:
         flags = set()
     
     stripped = list(argv) # copy
     
     swallow_next = False
     was_flag = False
     for a in argv:
         if a == '--':
             break
         if swallow_next:
             swallow_next = False
             # last arg was an alias, remove the next one
             # *unless* the last alias has a no-arg flag version, in which
             # case, don't swallow the next arg if it's also a flag:
             if not (was_flag and a.startswith('-')):
                 stripped.remove(a)
                 continue
         if a.startswith('-'):
             split = a.lstrip('-').split('=')
             name = split[0]
             # we use startswith because argparse accepts any arg to be specified
             # by any leading section, as long as it is unique,
             # so `--no-br` means `--no-browser` in the notebook, etc.
             if any(alias.startswith(name) for alias in aliases):
                 stripped.remove(a)
                 if len(split) == 1:
                     # alias passed with arg via space
                     swallow_next = True
                     # could have been a flag that matches an alias, e.g. `existing`
                     # in which case, we might not swallow the next arg
                     was_flag = name in flags
             elif len(split) == 1 and any(flag.startswith(name) for flag in flags):
                 # strip flag, but don't swallow next, as flags don't take args
                 stripped.remove(a)
     
     # return shortened list
     return stripped
 
 
 def make_ipkernel_cmd(code, executable=None, extra_arguments=[], **kw):
     """Build Popen command list for launching an IPython kernel.
 
     Parameters
     ----------
     code : str,
         A string of Python code that imports and executes a kernel entry point.
 
     executable : str, optional (default sys.executable)
         The Python executable to use for the kernel process.
 
     extra_arguments : list, optional
         A list of extra arguments to pass when executing the launch code.
     
     Returns
     -------
     
     A Popen command list
     """
     
     # Build the kernel launch command.
     if executable is None:
         executable = sys.executable
     arguments = [ executable, '-c', code, '-f', '{connection_file}' ]
     arguments.extend(extra_arguments)
 
     # Spawn a kernel.
     if sys.platform == 'win32':
 
         # If the kernel is running on pythonw and stdout/stderr are not been
         # re-directed, it will crash when more than 4KB of data is written to
         # stdout or stderr. This is a bug that has been with Python for a very
         # long time; see http://bugs.python.org/issue706263.
         # A cleaner solution to this problem would be to pass os.devnull to
         # Popen directly. Unfortunately, that does not work.
         if executable.endswith('pythonw.exe'):
             arguments.append('--no-stdout')
             arguments.append('--no-stderr')
 
     return arguments
 
 
 def launch_kernel(cmd, stdin=None, stdout=None, stderr=None, env=None,
                         independent=False,
                         cwd=None, ipython_kernel=True,
                         **kw
                         ):
     """ Launches a localhost kernel, binding to the specified ports.
 
     Parameters
     ----------
     cmd : Popen list,
         A string of Python code that imports and executes a kernel entry point.
 
     stdin, stdout, stderr : optional (default None)
         Standards streams, as defined in subprocess.Popen.
 
     independent : bool, optional (default False)
         If set, the kernel process is guaranteed to survive if this process
         dies. If not set, an effort is made to ensure that the kernel is killed
         when this process dies. Note that in this case it is still good practice
         to kill kernels manually before exiting.
 
     cwd : path, optional
         The working dir of the kernel process (default: cwd of this process).
 
     ipython_kernel : bool, optional
         Whether the kernel is an official IPython one,
         and should get a bit of special treatment.
 
     Returns
     -------
     
     Popen instance for the kernel subprocess
     """
 
     # Popen will fail (sometimes with a deadlock) if stdin, stdout, and stderr
     # are invalid. Unfortunately, there is in general no way to detect whether
     # they are valid.  The following two blocks redirect them to (temporary)
     # pipes in certain important cases.
 
     # If this process has been backgrounded, our stdin is invalid. Since there
     # is no compelling reason for the kernel to inherit our stdin anyway, we'll
     # place this one safe and always redirect.
     redirect_in = True
     _stdin = PIPE if stdin is None else stdin
 
     # If this process in running on pythonw, we know that stdin, stdout, and
     # stderr are all invalid.
     redirect_out = sys.executable.endswith('pythonw.exe')
     if redirect_out:
         _stdout = PIPE if stdout is None else stdout
         _stderr = PIPE if stderr is None else stderr
     else:
         _stdout, _stderr = stdout, stderr
     
+    env = env if (env is not None) else os.environ.copy()
+
     encoding = getdefaultencoding(prefer_stream=False)
     
     # Spawn a kernel.
     if sys.platform == 'win32':
         # Popen on Python 2 on Windows cannot handle unicode args or cwd
         cmd = [ cast_bytes_py2(c, encoding) for c in cmd ]
         if cwd:
             cwd = cast_bytes_py2(cwd, sys.getfilesystemencoding() or 'ascii')
         
         from IPython.kernel.zmq.parentpoller import ParentPollerWindows
         # Create a Win32 event for interrupting the kernel.
         interrupt_event = ParentPollerWindows.create_interrupt_event()
+        # Store this in an environment variable for third party kernels, but at
+        # present, our own kernel expects this as a command line argument.
+        env["IPY_INTERRUPT_EVENT"] = str(interrupt_event)
         if ipython_kernel:
             cmd += [ '--interrupt=%i' % interrupt_event ]
 
             # If the kernel is running on pythonw and stdout/stderr are not been
             # re-directed, it will crash when more than 4KB of data is written to
             # stdout or stderr. This is a bug that has been with Python for a very
             # long time; see http://bugs.python.org/issue706263.
             # A cleaner solution to this problem would be to pass os.devnull to
             # Popen directly. Unfortunately, that does not work.
             if cmd[0].endswith('pythonw.exe'):
                 if stdout is None:
                     cmd.append('--no-stdout')
                 if stderr is None:
                     cmd.append('--no-stderr')
 
         # Launch the kernel process.
         if independent:
             proc = Popen(cmd,
                          creationflags=512, # CREATE_NEW_PROCESS_GROUP
                          stdin=_stdin, stdout=_stdout, stderr=_stderr, env=env)
         else:
             if ipython_kernel:
                 try:
                     from _winapi import DuplicateHandle, GetCurrentProcess, \
                         DUPLICATE_SAME_ACCESS
                 except:
                     from _subprocess import DuplicateHandle, GetCurrentProcess, \
                         DUPLICATE_SAME_ACCESS
                 pid = GetCurrentProcess()
                 handle = DuplicateHandle(pid, pid, pid, 0,
                                          True, # Inheritable by new processes.
                                          DUPLICATE_SAME_ACCESS)
                 cmd +=[ '--parent=%i' % handle ]
             
             
             proc = Popen(cmd,
                          stdin=_stdin, stdout=_stdout, stderr=_stderr, cwd=cwd, env=env)
 
         # Attach the interrupt event to the Popen objet so it can be used later.
         proc.win32_interrupt_event = interrupt_event
 
     else:
         if independent:
             proc = Popen(cmd, preexec_fn=lambda: os.setsid(),
                          stdin=_stdin, stdout=_stdout, stderr=_stderr, cwd=cwd, env=env)
         else:
             if ipython_kernel:
                 cmd += ['--parent=1']
             proc = Popen(cmd,
                          stdin=_stdin, stdout=_stdout, stderr=_stderr, cwd=cwd, env=env)
 
     # Clean up pipes created to work around Popen bug.
     if redirect_in:
         if stdin is None:
             proc.stdin.close()
     if redirect_out:
         if stdout is None:
             proc.stdout.close()
         if stderr is None:
             proc.stderr.close()
 
     return proc
 
 __all__ = [
     'swallow_argv',
     'make_ipkernel_cmd',
     'launch_kernel',
 ]