respawn-exe-via-python.py

#!python

import sys
import time
import ctypes
import ctypes.wintypes
import subprocess

GetCurrentProcess = ctypes.windll.kernel32.GetCurrentProcess
GetCurrentProcess.argtypes = []
GetCurrentProcess.restype = ctypes.wintypes.HANDLE

# https://msdn.microsoft.com/en-us/library/windows/desktop/ms724251%28v=vs.85%29.aspx
DuplicateHandle = ctypes.windll.kernel32.DuplicateHandle
DuplicateHandle.argtypes = [
    # hSourceProcessHandle
    ctypes.wintypes.HANDLE,
    # hSourceHandle
    ctypes.wintypes.HANDLE,
    # hTargetProcessHandle
    ctypes.wintypes.HANDLE,
    # lpTargetHandle
    ctypes.wintypes.LPHANDLE,
    # dwDesiredAccess
    ctypes.wintypes.DWORD,
    # bInheritHandle
    ctypes.wintypes.BOOL,
    # dwOptions
    ctypes.wintypes.DWORD,
    ]
DuplicateHandle.restype = ctypes.wintypes.BOOL
DUPLICATE_SAME_ACCESS = 0x2

WaitForSingleObject = ctypes.windll.kernel32.WaitForSingleProcess
WaitForSingleObject.argtypes = [ctypes.wintypes.HANDLE, ctypes.wintypes.DWORD]
WaitForSingleObject.restype = ctypes.wintypes.DWORD
INFINITE = -1

CloseHandle = ctypes.windll.kernel32.CloseHandle
CloseHandle.argtypes = [ctypes.wintypes.HANDLE]
CloseHandle.restype = ctypes.wintypes.BOOL

if __name__ = "__main__":
    if "child" not in sys.argv:
        print("parent: starting")

        h = ctypes.wintypes.HANDLE(-1)
        me = GetCurrentProcess()
        if not DuplicateHandle(me, me, me,
                               ctypes.byref(h),
                               0, # ignored for DUPLICATE_SAME_ACCESS
                               ctypes.wintypes.BOOL(True), # inheritable
                               DUPLICATE_SAME_ACCESS):
            raise RuntimeError("failed to create inheritable process handle")
        print("parent: created handle to parent process, value =", h.value)

        print("parent: spawning child")
        # We have an inheritable HANDLE pointing to the parent process; pass
        # its value to the child so it can reconstitute it.
        # In real life for pip's purposes, we'd probably want to instead have
        # pip.exe spawn a call to something like:
        #     [sys.executable, "-m", "pip._windows_respawn", handle_value]
        #     + sys.argv[1:]
        p = subprocess.Popen([sys.executable, __file__,
                              "child", str(h.value)])

        print("parent: sleeping for 3 seconds...")
        time.sleep(3)

        print("parent: ...exiting")

    else:
        (_, child, parent_handle_str) = sys.argv
        assert child == "child"

        print("child: started, handle value is", parent_handle_str)
        h = ctypes.wintypes.HANDLE(int(parent_handle_str))

        print("child: waiting for parent to exit...")
        WaitForSingleObject(h, INFINITE)
        CloseHandle(h)

        print("child: parent has exited -- I'm free!")

        # now we are being run by python.exe, and our parent has exited, so we can safely write to our-parent.exe