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"""Utilities for launching kernels"""
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# Copyright (c) Jupyter Development Team.
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# Distributed under the terms of the Modified BSD License.
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import os
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import sys
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from subprocess import Popen, PIPE
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from IPython.utils.encoding import getdefaultencoding
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from IPython.utils.py3compat import cast_bytes_py2
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def launch_kernel(cmd, stdin=None, stdout=None, stderr=None, env=None,
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independent=False,
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cwd=None,
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**kw
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):
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""" Launches a localhost kernel, binding to the specified ports.
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Parameters
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----------
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cmd : Popen list,
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A string of Python code that imports and executes a kernel entry point.
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stdin, stdout, stderr : optional (default None)
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Standards streams, as defined in subprocess.Popen.
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independent : bool, optional (default False)
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If set, the kernel process is guaranteed to survive if this process
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dies. If not set, an effort is made to ensure that the kernel is killed
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when this process dies. Note that in this case it is still good practice
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to kill kernels manually before exiting.
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cwd : path, optional
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The working dir of the kernel process (default: cwd of this process).
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Returns
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-------
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Popen instance for the kernel subprocess
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"""
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# Popen will fail (sometimes with a deadlock) if stdin, stdout, and stderr
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# are invalid. Unfortunately, there is in general no way to detect whether
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# they are valid. The following two blocks redirect them to (temporary)
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# pipes in certain important cases.
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# If this process has been backgrounded, our stdin is invalid. Since there
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# is no compelling reason for the kernel to inherit our stdin anyway, we'll
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# place this one safe and always redirect.
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redirect_in = True
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_stdin = PIPE if stdin is None else stdin
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# If this process in running on pythonw, we know that stdin, stdout, and
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# stderr are all invalid.
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redirect_out = sys.executable.endswith('pythonw.exe')
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if redirect_out:
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blackhole = open(os.devnull, 'w')
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_stdout = blackhole if stdout is None else stdout
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_stderr = blackhole if stderr is None else stderr
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else:
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_stdout, _stderr = stdout, stderr
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env = env if (env is not None) else os.environ.copy()
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encoding = getdefaultencoding(prefer_stream=False)
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kwargs = dict(
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stdin=_stdin,
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stdout=_stdout,
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stderr=_stderr,
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cwd=cwd,
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env=env,
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)
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# Spawn a kernel.
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if sys.platform == 'win32':
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# Popen on Python 2 on Windows cannot handle unicode args or cwd
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cmd = [ cast_bytes_py2(c, encoding) for c in cmd ]
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if cwd:
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cwd = cast_bytes_py2(cwd, sys.getfilesystemencoding() or 'ascii')
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kwargs['cwd'] = cwd
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from .win_interrupt import create_interrupt_event
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# Create a Win32 event for interrupting the kernel
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# and store it in an environment variable.
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interrupt_event = create_interrupt_event()
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env["JPY_INTERRUPT_EVENT"] = str(interrupt_event)
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# deprecated old env name:
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env["IPY_INTERRUPT_EVENT"] = env["JPY_INTERRUPT_EVENT"]
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try:
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from _winapi import DuplicateHandle, GetCurrentProcess, \
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DUPLICATE_SAME_ACCESS, CREATE_NEW_PROCESS_GROUP
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except:
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from _subprocess import DuplicateHandle, GetCurrentProcess, \
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DUPLICATE_SAME_ACCESS, CREATE_NEW_PROCESS_GROUP
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# Launch the kernel process
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if independent:
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kwargs['creationflags'] = CREATE_NEW_PROCESS_GROUP
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else:
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pid = GetCurrentProcess()
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handle = DuplicateHandle(pid, pid, pid, 0,
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True, # Inheritable by new processes.
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DUPLICATE_SAME_ACCESS)
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env['JPY_PARENT_PID'] = str(int(handle))
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proc = Popen(cmd, **kwargs)
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# Attach the interrupt event to the Popen objet so it can be used later.
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proc.win32_interrupt_event = interrupt_event
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else:
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if independent:
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kwargs['preexec_fn'] = lambda: os.setsid()
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else:
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env['JPY_PARENT_PID'] = str(os.getpid())
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proc = Popen(cmd, **kwargs)
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# Clean up pipes created to work around Popen bug.
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if redirect_in:
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if stdin is None:
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proc.stdin.close()
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return proc
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__all__ = [
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'launch_kernel',
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]
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