win32process.CreateProcess inherit handles not working ?

[David Bolen]

teyc at cognoware.com (Chui Tey) writes:

> I've been trying to get this going for a while and I'd appreciate it
> if someone can point out what's wrong with the following test? It works
> fine on Win98 but fails on NT and W2K. I am using Python 2.1

I don't know that this is the most elegant solution, but I've used
DuplicateHandle rather than security attributes to create inheritable
handles in the past successfully.  It was a while ago, but I seem to
recall getting into trouble with SAs because they also include the
DACL which defaults to no access unless you explicitly assign it a
NULL DACL, and it's just sort of a pain in the neck in terms of extra
steps just to inherit the darn handle properly.

I don't know that it's what is happening here, but perhaps Win98 is
ignoring the security information whereas NT/W2K aren't.  I tried
modifying your code to use DuplicateHandle and it seems to work fine
on my NT4 SP5 system.

I'm sure there's a way to make it work with a security attribute as
well (and avoid the extra file handle), but this isn't all that bad.

So something like:

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def _CreateProcess(app, args, filein, fileout):

    """Returns the pid.
       app = executable name
       args = list of arguments
       filein = name of file to redirect to stdin
       fileout = name of file to redirect the stdout to
    """
 
    import win32process
    import win32file
    import pywintypes
    import win32event
    import win32api
    import win32con

    u_filein = pywintypes.Unicode(filein)
    u_fileout = pywintypes.Unicode(fileout)

    SI = win32process.GetStartupInfo()
    SI.dwFlags = win32process.STARTF_USESTDHANDLES
    
    hInput = win32file.CreateFile(
        u_filein,                   # filename
        win32file.GENERIC_READ,     # mode
        win32file.FILE_SHARE_READ,  # share
        None,                       # security attributes 
        win32file.OPEN_EXISTING,    # creation disposition
        win32file.FILE_ATTRIBUTE_NORMAL, # flags
        0                           # hTemplate file
    )
    hOutput = win32file.CreateFile(
        u_fileout,                  # filename
        win32file.GENERIC_WRITE,    # mode
        win32file.FILE_SHARE_WRITE, # share
        None,                       # security attributes 
        win32file.CREATE_ALWAYS,    # creation disposition
        win32file.FILE_ATTRIBUTE_NORMAL, # flags
        0                           # hTemplate file
    )

    hStdInput = win32api.DuplicateHandle(win32api.GetCurrentProcess(),
                                         hInput,
                                         win32api.GetCurrentProcess(),
                                         0,1,
                                         win32con.DUPLICATE_SAME_ACCESS)
    hStdOutput = win32api.DuplicateHandle(win32api.GetCurrentProcess(),
                                          hOutput,
                                          win32api.GetCurrentProcess(),
                                          0,1,
                                          win32con.DUPLICATE_SAME_ACCESS)

    SI.hStdInput = hStdInput
    SI.hStdOutput = hStdOutput
    SI.hStdError  = hStdOutput

    cmdline = app + " " + " ".join(args)
    hProcess, hThread, pid, threadid =  \
        win32process.CreateProcess( 
        app,                    # lpApplicationName
        cmdline,                # command line
        None,                   # Process security attributes
        None,                   # Thread security attributes
        1,                      # Inherit handles
        win32process.DETACHED_PROCESS,  #
        None, 
        None, 
        SI)

    win32event.WaitForSingleObject(hProcess, win32event.INFINITE)

    win32file.CloseHandle(hInput)
    win32file.CloseHandle(hOutput)
    win32file.CloseHandle(hStdInput)
    win32file.CloseHandle(hStdOutput)
    
    return pid
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--
-- David
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