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Re: windows bug: filewritable() returns 0 if we use it on the current script being read

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  • Philippe Vaucher
    ... I don t know how I can make sure this doens t make any trouble... but if your question is if CreateFile() s dwShareMode flag is supported on all flavors of
    Message 1 of 16 , Nov 3, 2010
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      > It makes sense, but we must make sure this does not cause any trouble.
      > Does it work on all Windows versions?

      I don't know how I can make sure this doens't make any trouble... but
      if your question is if CreateFile()'s dwShareMode flag is supported on
      all flavors of windows I think the answer is yes. Based on
      http://msdn.microsoft.com/en-us/library/aa363874(v=VS.85).aspx and on
      http://msdn.microsoft.com/en-us/library/aa363858(VS.85).aspx it looks
      like CreateFile goes back to windows 2000.

      I'm pretty new to digging into vim's source so I don't know if windows
      98 is supported (I was also a bit surprised by the old-style function
      declarations :).

      Anyway, I guess I could simply build vim and check if the problem goes
      away if I add the relevant flag everywhere CreateFile is used, but how
      do I make sure it didn't break other stuffs? My instincts tell me this
      should not create any problem as you'd normally not care about any
      file being already opened or not, but maybe I'm wrong, and I'm not
      sure about what I should test to assert at least the basic stuffs work
      as expected beside opening some files and checking my vim still
      works :)


      > On Unix we never care about others having the file open, thus I don't
      > see a reason to check for that on MS-Windows.

      Well yes on Unix the behavior is to permit others to open the file, so
      the current windows behavior differs in that respect.

      Thanks,
      Philippe

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    • Philippe Vaucher
      ... This bug arised from a script that checked wether itself was writable in order to decide to go and write to the parent directory or go to alternate routes
      Message 2 of 16 , Nov 3, 2010
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        > I'm pretty sure you nomally WANT to lock a file from being written,
        > while you are executing its contents as a script. It sounds like this
        > is what is happening. Is there some reason you want to write the file
        > while executing it?

        This bug arised from a script that checked wether itself was writable
        in order to decide to go and write to the parent directory or go to
        alternate routes like ~/.vim etc. If you want more details I'll be
        happy to provide them but the point is that if such behavior is
        enabled in *nix it'd also be enabled in windows or disabled in both.

        The thing I'm really after is consistency, the fix for the particular
        script was to change it to check the script's directory instead which
        works consistently on both platforms.

        Philippe

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      • Craig Barkhouse
        ... Changing the share mode to (FILE_SHARE_READ | FILE_SHARE_WRITE) in mch_access() is theoretically safe, because mch_access() doesn t do any I/O and closes
        Message 3 of 16 , Nov 3, 2010
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          Phillippe Vaucher wrote:

          > > I'm pretty sure you nomally WANT to lock a file from being written,
          > > while you are executing its contents as a script. It sounds like this
          > > is what is happening. Is there some reason you want to write the file
          > > while executing it?
          >
          > This bug arised from a script that checked wether itself was writable in order to
          > decide to go and write to the parent directory or go to alternate routes like
          > ~/.vim etc. If you want more details I'll be happy to provide them but the point is
          > that if such behavior is enabled in *nix it'd also be enabled in windows or
          > disabled in both.
          >
          > The thing I'm really after is consistency, the fix for the particular script was to
          > change it to check the script's directory instead which works consistently on
          > both platforms.
          >
          > Philippe

          Changing the share mode to (FILE_SHARE_READ | FILE_SHARE_WRITE) in mch_access() is theoretically safe, because mch_access() doesn't do any I/O and closes the handle immediately. It would not be ok to make a broader change throughout the source code to always open handles with more permissive sharing. When you use those share modes, basically you're saying "I'm opening a file handle now, and I really don't care if anyone else is reading and/or writing the file at the same time as I'm working with the file." In general you do care. If you're writing to a file, you don't want another process also writing, which would result in undefined file contents. You don't really want one process reading while another process is writing either, because then the reader will see an inconsistent view. The only type of sharing that is typically safe is read-read.

          Assuming you don't want permissive sharing when doing actual I/O (I argue above that you don't), I question the value of changing mch_access() in the proposed way. The point of mch_access() is to give you a predictor of what types of access will likely work. If the access check tells you that opening the file for write will work, but then when you actually open it for write (using realistic sharing values) it fails, isn't this worse than what we have now?

          The proposed change to mch_access() would only address a narrow scenario anyway. It allows you to avoid a sharing violation imposed by *your* handle. You'll still see sharing violations imposed by *other* handles. The general rule is that the access mode of any opened handle must be compatible with the share mode of all other opened handles.

          Craig

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        • John Beckett
          ... Although I haven t followed exactly what the OP is proposing, what Craig says is correct. Allowing multiple writers to the same file is only desirable
          Message 4 of 16 , Nov 3, 2010
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            Craig Barkhouse wrote:
            > Assuming you don't want permissive sharing when doing actual
            > I/O (I argue above that you don't), I question the value of
            > changing mch_access() in the proposed way. The point of
            > mch_access() is to give you a predictor of what types of
            > access will likely work. If the access check tells you that
            > opening the file for write will work, but then when you
            > actually open it for write (using realistic sharing values)
            > it fails, isn't this worse than what we have now?

            Although I haven't followed exactly what the OP is proposing,
            what Craig says is correct. Allowing multiple writers to the
            same file is only desirable under very planned circumstances
            which do NOT include a text editor writing to a file.

            John

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          • Philippe Vaucher
            ... As I said I m pretty fine with this way of seeing things, but then it means the bug is in the current *nix version. IMHO vim should behave as
            Message 5 of 16 , Nov 4, 2010
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              > > Assuming you don't want permissive sharing when doing actual
              > > I/O (I argue above that you don't), I question the value of
              > > changing mch_access() in the proposed way.  The point of
              > > mch_access() is to give you a predictor of what types of
              > > access will likely work.  If the access check tells you that
              > > opening the file for write will work, but then when you
              > > actually open it for write (using realistic sharing values)
              > > it fails, isn't this worse than what we have now?
              >
              > Although I haven't followed exactly what the OP is proposing,
              > what Craig says is correct. Allowing multiple writers to the
              > same file is only desirable under very planned circumstances
              > which do NOT include a text editor writing to a file.

              As I said I'm pretty fine with this way of seeing things, but then it
              means the "bug" is in the current *nix version. IMHO vim should behave
              as consistently as possible on the platforms it runs on, thus we'd
              then change the *nix api to behave like the current win32 one.

              Also, the way vim behaves on win32 about this is probably
              inconsistent, as a test script I did the following:

              echo 'writable: ' . filewritable(expand('<sfile>'))
              write!

              When I do ":source %" it output writable: 0, then writes the file
              anyway :)

              So I *think* that originally the vim authors never intended to prevent
              other processes/whatever from begin able to open the same files, only
              that on windows on some occasions the authors got lazy and forgot
              about the dwSharedMode flag and just set it to 0. Someone should
              decide wether we want to prevent it or not and then implement it on
              all the platforms.

              Philippe

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            • Philippe Vaucher
              So, who has to authority on this? Should we allow multiple writers to a file? Should we allow writers on currently read file? If no how drastics are the
              Message 6 of 16 , Nov 7, 2010
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                So, who has to authority on this? Should we allow multiple writers to
                a file? Should we allow writers on currently read file? If no how
                drastics are the changes to be made to the linux api?

                Philippe

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              • Roland Puntaier
                Hi Bram, After installing vim7.3 on a ubuntu system, I had again the problem that import did not work for .so libraries in lib-dynload. I found that sys.path
                Message 7 of 16 , Nov 7, 2010
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                  Hi Bram,

                  After installing vim7.3 on a ubuntu system, I had again the problem that
                  import did not work for .so libraries in lib-dynload. I found that
                  sys.path was initialized with "/usr/..." instead of "/usr/local/...". On
                  ubuntu (and probably on other linux distros as well) python3 is
                  installed in /usr/local while python2 is installed in /usr.

                  The attached patch calls Py_SetPythonHome with PYTHON3_PREFIX defined by
                  configure.
                  This solves the problem.

                  regards, Roland
                • James Vega
                  ... That s not the case at all[0]. No distribution package should install to /usr/local as that s a reserved directory structure for the system
                  Message 8 of 16 , Nov 7, 2010
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                    On Sun, Nov 07, 2010 at 06:04:35PM +0200, Roland Puntaier wrote:
                    > Hi Bram,
                    >
                    > After installing vim7.3 on a ubuntu system, I had again the problem
                    > that import did not work for .so libraries in lib-dynload. I found
                    > that sys.path was initialized with "/usr/..." instead of
                    > "/usr/local/...". On ubuntu (and probably on other linux distros as
                    > well) python3 is installed in /usr/local while python2 is installed
                    > in /usr.

                    That's not the case at all[0]. No distribution package should install
                    to /usr/local as that's a reserved directory structure for the system
                    administrator[1]. If your Python3 install is in /usr/local, then whoever
                    admins that system installed it there.

                    > The attached patch calls Py_SetPythonHome with PYTHON3_PREFIX
                    > defined by configure.
                    > This solves the problem.

                    This does make sense for supporting people who have installed Python
                    outside of the standard paths, though. This should probably be done for
                    Python2.x as well.

                    [0]: http://packages.ubuntu.com/maverick/i386/python3.1/filelist
                    [1]: http://www.pathname.com/fhs/pub/fhs-2.3.html#USRLOCALLOCALHIERARCHY
                    --
                    James
                    GPG Key: 1024D/61326D40 2003-09-02 James Vega <jamessan@...>
                  • James Vega
                    ... Would it make more sense to use Py_GetPrefix() or Py_GetExecPrefix() as the input to Py_SetPythonHome() instead? -- James GPG Key: 1024D/61326D40
                    Message 9 of 16 , Nov 7, 2010
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                      On Sun, Nov 07, 2010 at 01:53:05PM -0500, James Vega wrote:
                      > On Sun, Nov 07, 2010 at 06:04:35PM +0200, Roland Puntaier wrote:
                      > > The attached patch calls Py_SetPythonHome with PYTHON3_PREFIX
                      > > defined by configure.
                      > > This solves the problem.
                      >
                      > This does make sense for supporting people who have installed Python
                      > outside of the standard paths, though. This should probably be done for
                      > Python2.x as well.

                      Would it make more sense to use Py_GetPrefix() or Py_GetExecPrefix() as the
                      input to Py_SetPythonHome() instead?

                      --
                      James
                      GPG Key: 1024D/61326D40 2003-09-02 James Vega <jamessan@...>
                    • Philippe Vaucher
                      ... Why the hell happened there? Seems you replied to the wrong thread and managed to change the subject. Look at
                      Message 10 of 16 , Nov 7, 2010
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                        > After installing vim7.3 on a ubuntu system, I had again the problem that
                        > import did not work for .so libraries in lib-dynload. I found that
                        > sys.path was initialized with "/usr/..." instead of "/usr/local/...". On
                        > ubuntu (and probably on other linux distros as well) python3 is
                        > installed in /usr/local while python2 is installed in  /usr.
                        >
                        > The attached patch calls Py_SetPythonHome with PYTHON3_PREFIX defined by
                        > configure.
                        > This solves the problem.


                        Why the hell happened there? Seems you replied to the wrong thread and
                        managed to change the subject.

                        Look at http://groups.google.com/group/vim_dev/browse_thread/thread/6972ae8d369cf671/a183f61488f3006c#

                        Philippe

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                      • Roland Puntaier
                        ... OK, maybe I didn t use apt-get. Nevertheless, as most original sources do, python 3.x defaults to /usr/local prefix. And anyway, for the problem, it
                        Message 11 of 16 , Nov 7, 2010
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                          James Vega wrote:
                          > On Sun, Nov 07, 2010 at 06:04:35PM +0200, Roland Puntaier wrote:
                          >
                          >> Hi Bram,
                          >>
                          >> After installing vim7.3 on a ubuntu system, I had again the problem
                          >> that import did not work for .so libraries in lib-dynload. I found
                          >> that sys.path was initialized with "/usr/..." instead of
                          >> "/usr/local/...". On ubuntu (and probably on other linux distros as
                          >> well) python3 is installed in /usr/local while python2 is installed
                          >> in /usr.
                          >>
                          >
                          > That's not the case at all[0]. No distribution package should install
                          > to /usr/local as that's a reserved directory structure for the system
                          > administrator[1]. If your Python3 install is in /usr/local, then whoever
                          > admins that system installed it there.
                          >
                          OK, maybe I didn't use apt-get. Nevertheless, as most original sources do,
                          python 3.x defaults to /usr/local prefix. And anyway, for the problem,
                          it doesn't matter how it got there.
                          >> The attached patch calls Py_SetPythonHome with PYTHON3_PREFIX
                          >> defined by configure.
                          >> This solves the problem.
                          >>
                          >
                          > This should probably be done for Python2.x as well.
                          >
                          Yeah, you are right. I will send a new patch soon.

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                        • Roland Puntaier
                          ... Sorry Philippe, Using Thunderbird I ve chosen an arbitrary message from vim_dev and changed subject and body. I didn t know that the threading is done on
                          Message 12 of 16 , Nov 7, 2010
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                            Philippe Vaucher wrote:
                            >
                            > Why the hell happened there? Seems you replied to the wrong thread and
                            > managed to change the subject.
                            >
                            > Look at http://groups.google.com/group/vim_dev/browse_thread/thread/6972ae8d369cf671/a183f61488f3006c#
                            >
                            > Philippe
                            >
                            >
                            Sorry Philippe,

                            Using Thunderbird I've chosen an arbitrary message from vim_dev and
                            changed subject and body.

                            I didn't know that the threading is done on invisible email message
                            fields other than the subject. I looked at the email source and found
                            fields like References and In-Reply-To.

                            There is always something new to learn. For my next message I'll take it
                            into account.

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