On Windows, Python uses the POSIX API (file descriptors), instead of the native API (file handles). Some features cannot be used using the POSIX API, like setting security attributes. It would be nice to have a io.FileIO using Windows file handlers to get access to all Windows features. It would help feature #12105 to implement "O_CLOEXEC" flag using the lpSecurityAttributes argument.

We can maybe try with a prototype written in Python. Using _pyio.RawIOBase, only readinto(), write(), seek() and truncate() have to be implemented. But it is better to implement also close() :-)

See also issue #1602: a prototype of a console object has been proposed to use the native Windows console API, instead of the POSIX API (read from fd 0, write to fd 1 or 2). The prototype is implemented in Python using ctypes.

Instead of rewriting your own RawIO implementation, why not use _open_osfhandle?
This should be simple now with the "opener" argument.
http://msdn.microsoft.com/en-us/library/bdts1c9x.aspx

why not use _open_osfhandle?

Because it is wrapper for other CRT functions for Windows, like close(). In other words it is an emulation. I think Python should not create wrapper around wrapper around wrapper...

For example, in Python3, open() implemented using open() and not using fopen(). Why we should use another wrapper on Windows platform?

> why not use _open_osfhandle?
> 
> Because it is wrapper for other CRT functions for Windows, like
> close(). In other words it is an emulation. I think Python should not
> create wrapper around wrapper around wrapper...

Why do you think it makes a difference?

An implementation of RawIO with the win32 API can be useful (and I'd be interested to compare the performance)
But maybe not for all usages: some Python interfaces are defined in terms of file descriptors, imp.load_module(), and PyTokenizer_FindEncoding for example.

> Why do you think it makes a difference?
Because adding one more dependency on unneeded libraries add the pain. Also it limit us on very restricted API of that wrapper. Windows native API is stable. So it's OK to rely on it's documented imlementation.

Suppose, we receive file-descriptor from _open_osfhandle.... For example it is a socket. It still unusable for stdin. Many standard functions does not work with such handle. The list of available functions : http://msdn.microsoft.com/en-us/library/kdfaxaay.aspx . As we see it is very narrow and function names are not POSIX-compatible (_chsize vs ftruncate). Documentation is very poor. For example, _close() is documented only here: http://msdn.microsoft.com/en-US/library/40bbyw78(v=VS.80).aspx .

The good example of implemetation is QT. I think we can get some things from this library. (Like using  "\\?\" for long paths (or always, as in QT)).

> > Why do you think it makes a difference?
> Because adding one more dependency on unneeded libraries add the pain.

MSVCRT is unneeded?? What are you talking about?

> Also it limit us on very restricted API of that wrapper. Windows
> native API is stable. So it's OK to rely on it's documented
> imlementation.

Please provide a patch to demonstrate the claimed improvement.

> Like using  "\\?\" for long paths

That's completely unrelated to this issue.

> Instead of rewriting your own RawIO implementation, why not use
> _open_osfhandle?

I don't know yet what is the best approach. One important point is to keep the 
HANDLE, to be able to manipulate the open file using the Windows API (e.g. call 
WriteFile instead of write).

I propose a RawIO to call directly the Windows API: file.write() would call 
directly WriteFile() instead of the POSIX wrapper (write()).

We may use it to implement new features like async I/O on Windows (e.g. 
WriteFileEx).

Modules/_multiprocessing/win32_functions.c exposes already some low-level 
Windows functions like WriteFile(). We may reuse the RawIO to offer an object 
oriented API for the Windows multiprocessing pipes. Such RawIO would have 
extra methods, maybe a file.WriteFile() method to give access to extra options 
like "overlapped".

I'm not really motivated to work on a Windows-specific issue. The issue has no patch, even no proof-of-concept implemented in Python. Can I close the issue, or is someone interested to work on this topic?

Python 3.3 adds a opener argument to open(). It may be enough to workaround this issue?

Yes, re-writing windows IO to direct API, without intemediate layer is still needed.

Please don't close bug. Maybe someone will implement this.

A while ago I did write a PipeIO class which subclasses io.RawIOBase and works for overlapped pipe handles.  (It was intended for multiprocessing and doing asynchronous IO with subprocess.)

As it is it would not work with normal files because when you do overlapped IO on files you must manually track the file position.

> Yes, re-writing windows IO to direct API, without intemediate layer is still 
> needed.

What are the expected benefits?

> It would help feature #12105 to implement "O_CLOEXEC" flag using the 
> lpSecurityAttributes argument.

Isn't O_NOINHERIT the Windows equivalent of O_CLOEXEC?

Attached is a module for Python 3.3+ which subclasses io.RawIOBase.  The constructor signature is

    WinFileIO(handle, mode="r", closehandle=True)

where mode is "r", "w", "r+" or "w+".  Handles can be created using _winapi.CreateFile().

Issues:
- No support for append mode.
- Truncate is not atomic.  (Is atomicity supposed to be guaranteed?)
- Not properly tested.

Attached is a patch which adds a winio module which is a replacement for io, but uses windows handles instead of fds.

It reimplements FileIO and open(), and provides openhandle() and closehandle() as replacements for os.open() and os.close().

test_io has been modified to exercise winio (in addition to _io and _pyio) and all the tests pass.

Note that some of the implementation (openhandle(), open(), FileIO.__init__()) is still done in Python rather than C.

I don't like the idea of a specific I/O module for an OS. Is the public API
different? Can't you reuse the io module?
Le 6 janv. 2013 14:59, "Richard Oudkerk" <report@bugs.python.org> a écrit :

>
> Richard Oudkerk added the comment:
>
> Attached is a patch which adds a winio module which is a replacement for
> io, but uses windows handles instead of fds.
>
> It reimplements FileIO and open(), and provides openhandle() and
> closehandle() as replacements for os.open() and os.close().
>
> test_io has been modified to exercise winio (in addition to _io and _pyio)
> and all the tests pass.
>
> Note that some of the implementation (openhandle(), open(),
> FileIO.__init__()) is still done in Python rather than C.
>
> ----------
> keywords: +patch
> Added file: http://bugs.python.org/file28590/winfileio.patch
>
> _______________________________________
> Python tracker <report@bugs.python.org>
> <http://bugs.python.org/issue12939>
> _______________________________________
>

> I don't like the idea of a specific I/O module for an OS. Is the public API
> different?

It was partly to make integration with the existing tests easier: _io, _pyio and winio are tested in parallel.

> Can't you reuse the io module?

In what sense?

I don't really know how the API should be exposed.

Hum, _get_osfhandle() was not mentionned in this issue. This function may be used to retrieve the internel file handle from a file descriptor.
http://msdn.microsoft.com/en-us/library/ks2530z6%28v=vs.100%29.aspx

There is also the opposite: _open_osfhandle(). This function may be used for fileno() method of the Windows implementation of FileIO.
http://msdn.microsoft.com/en-us/library/bdts1c9x%28v=vs.100%29.aspx

Attached is a new patch which is implemented completely in C.

It adds a WinFileIO class to the io module, which has the same API 
as FileIO except that:

* It has a handle attribute instead of a fileno() method.

* It has staticmethods openhandle() and closehandle() which are
  analogues of os.open() and os.close().

The patch also adds a keyword-only "rawfiletype" argument to
io.open() so that you can write

    f = open("somefile", "w", rawfiletype=WinFileIO)

Forgot to mention, the handles are non-inheritable.

You can use _winapi.DuplicateHandle() to create an inheritable duplicate handle if you really need to.

Added some comments on Rietveld.
The .fileno() method is missing. Can this cause a problem when the file is passed to stdlib functions? subprocess for example?

What does this proposal bring exactly?

> Added some comments on Rietveld.
> The .fileno() method is missing. Can this cause a problem when the file 
> is passed to stdlib functions? subprocess for example?

Thanks.  An older version of the patch had a fileno() method which returned the handle -- but that would have confused anything that expects fileno() to return a true fd.

It would be possible to make fileno() lazily create an fd using open_osfhandle().

> What does this proposal bring exactly?

Unless we are willing to completely replace fds with handles on Windows, perhaps not too much.  (At one point I had assumed that that was the plan for py3k.)

Although not advertised, openhandle() does have a share_flags parameter to control the share mode of the file.  This makes it possible to delete files for which there are open handles.  Mercurial needs a C extension to support this.  regrtest could certainly benefit from such a feature.

But one thing that I would at least like to do is create a FileIO replacement for overlapped pipe/socket handles.  Then multiprocessing.Connection could be a simple wrapper round a file object, and most of the platform specific code in multiprocessing.connection can go away.

The current patch does not support overlapped IO, but that could be added easily enough.  (Overlapped IO for normal files might be more complicated.)

New patch reflecting Amaury's comments.

> The current patch does not support overlapped IO, but that could be
> added easily enough.  (Overlapped IO for normal files might be more
> complicated.)

That could be cool. Wouldn't it belong in the fabled winapi module?

Just a note of support for Richard -- having I/O use the native APIs directly rather than via emulation or other wrappers is a good idea, because the emulations / wrappers usually add restrictions that are not present in the native API.  This is also the reason why we dropped going through stdio -- it did not give enough control over buffering and made integration with (UNIX native) file descriptors complex.  Integration with native I/O primitives on Windows seems sense in the light of e.g. PEP 3156.

I guess extracting Richard's patch to a package and placing it on PyPI would be a good move. I recalled reading this bug after I saw "Does Python IO allow opened file to be deleted/renamed on Windows?" question on Stackoverflow (http://stackoverflow.com/q/19280836/95735)

It strikes me as far more sense to use the native API so how do we take this forward, formal patch review, put it on pypi, or what?

Serhiy implemented the FileIO class in pure Python: see the issue #21859 (patch under review). Using thre Python class, it becomes easier to reimplement FileIO using the Windows API, at least to play with a prototype in pure Python.

Lack of interest, I'm not convinced that it's *really* needed. We survived 8 years with the current io module in Python 3, it's probably enough. I close the issue.

Please reopen. I still have interest for that. Fact that we survive 8 years is not enough for closing bugs as "Won't fix".

This fact point only on that ther are no good specialists that can fix that bug, since it is Windows-only, actually.

Sorry, for the "there are no good specialist". I mean "There are no well motivated good specialist" :)

Since Guido voted in favor and there's a patch proposal, I think we should keep this open in the hopes that someone will come along who can move it forward.  I don't know enough to know what moving it forward would look like, though.

(I know you opened the issue originally, Victor, and you aren't interested in it any more, but obviously others are.)

If Марк Коренберг (mmarkk) is interested, they should move it forward.  If they're not interested, move it too "languishing", where it can sit happily for ever and a day.  Pay your money, take your choice?

I reopen the issue. The patch is outdated. Richard Oudkerk doens't seem to be active last weeks :-/

While it might be a good idea, we failed to find anyone to implement it in 6 years, and so I close the issue. Sorry!

If it's a good idea, why close the issue?  Maybe post it to core-mentorship instead?  It's not an easy issue, but it also has the beginnings of a patch.  So if there is anyone on core-mentorship with some windows knowledge (and I'm guessing their are), maybe they'd be interested in the challenge.

R. David Murray: "If it's a good idea, why close the issue?"

Yesterday I tried to cleanup the list of issues that I opened. I reduced my list from 140 to around 100 issues. I'm happier :-) I don't like having a too long "TODO list".

Sometimes, closing an issue helps to shake up people and it can even unblock an old issue :-)

In this case, I already closed and then reopened the issue, and nothing happened.

The benefit doesn't seem worth it, compared to the risk of backward compatibility issue and the cost of maintaining this new code.


"Maybe post it to core-mentorship instead?  It's not an easy issue, but it also has the beginnings of a patch."

Sorry, but it's very far from an easy issue. It seems like even our existing Windows experts failed to implement the feature in 6 years. I don't expect that any newcomer will success to fix the technical issues, especially if nobody is available to answer to the newcomer questions...

It's not because an issue is closed that the data that it contains is definitevely lost. If someone wants to work on that issue, it will be easy to find this issue using a Google search.

I see open issues as "bugs that must be fixed" or "important missing features", not as an unlimited wishlist. I know that each developer uses a bug tracker differently ;-)

At least, I don't want to the author of such wishlist issue anymore, and I don't want how to change the author of an issue. So I will continue to close it regulary to reduce my list of open issues (that I opened). Again, it's important for me to keep this list as short as possible.

Given that background, closing it seems reasonable to me :)