Wednesday, January 02, 2013

Python: get parent process id (pid) in windows

Below is code to monkey-patch the os module to provide a getppid() function to get the parent process id in windows using ctypes (note that on Python 3.2, os.getppid() already works and is available on windows, but if you're on an older version, this can be used as a workaround).

import os
if not hasattr(os, 'getppid'):
    import ctypes

    CreateToolhelp32Snapshot = ctypes.windll.kernel32.CreateToolhelp32Snapshot
    GetCurrentProcessId = ctypes.windll.kernel32.GetCurrentProcessId

    MAX_PATH = 260

    _kernel32dll = ctypes.windll.Kernel32
    CloseHandle = _kernel32dll.CloseHandle

    class PROCESSENTRY32(ctypes.Structure):
        _fields_ = [
            ("dwSize", ctypes.c_ulong),
            ("cntUsage", ctypes.c_ulong),
            ("th32ProcessID", ctypes.c_ulong),
            ("th32DefaultHeapID", ctypes.c_int),
            ("th32ModuleID", ctypes.c_ulong),
            ("cntThreads", ctypes.c_ulong),
            ("th32ParentProcessID", ctypes.c_ulong),
            ("pcPriClassBase", ctypes.c_long),
            ("dwFlags", ctypes.c_ulong),

            ("szExeFile", ctypes.c_wchar * MAX_PATH)

    Process32First = _kernel32dll.Process32FirstW
    Process32Next = _kernel32dll.Process32NextW

    def getppid():
        :return: The pid of the parent of this process.
        pe = PROCESSENTRY32()
        pe.dwSize = ctypes.sizeof(PROCESSENTRY32)
        mypid = GetCurrentProcessId()
        snapshot = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0)

        result = 0
            have_record = Process32First(snapshot, ctypes.byref(pe))

            while have_record:
                if mypid == pe.th32ProcessID:
                    result = pe.th32ParentProcessID

                have_record = Process32Next(snapshot, ctypes.byref(pe))


        return result

    os.getppid = getppid

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