3.3.0: Possible regression in cygwin DLL (Win10); fixed in snapshot

Corinna Vinschen corinna-cygwin@cygwin.com
Thu Nov 11 11:33:21 GMT 2021


On Nov 11 20:12, Takashi Yano wrote:
> On Thu, 11 Nov 2021 10:52:33 +0100
> Corinna Vinschen wrote:
> > On Nov 10 21:35, Corinna Vinschen wrote:
> > > On Nov 10 22:30, Takashi Yano wrote:
> > > > On Wed, 10 Nov 2021 11:34:25 +0100
> > > > Corinna Vinschen wrote:
> > > > > On Nov 10 17:30, Takashi Yano wrote:
> > > > > > So I would like to propose alternative implementation with
> > > > > > FILE_SYNCHRONOUS_IO_NONALERT being set. Please have a look
> > > > > > at attached patch. With this patch, pipe itself in read side
> > > > > > is always set to nonblocking mode and simulate the blocking
> > > > > > behaviour in raw_read(). This can eliminate creating thread
> > > > > > for reading as well as calling CancelSynchronousIo().
> > > > > > 
> > > > > > Note that setting FILE_SYNCHRONOUS_IO_NONALERT only for read
> > > > > > pipe seems to be enough for C# programs.
> > > > > > 
> > > > > > What do you think of this implementation?
> > > > > [...]
> > What I like with this approach is that it actually simplifies the code.
> > 
> > What I don't like much is that we are now running a busy loop, but the
> > NtQueryObject hang is... disappointing, to say the least.  What about
> > using another function like NtQueryInformationFile(FileNameInformation)?
> > I bet this hangs, too, right?  
> 
> I have just confirmed that NtQueryInformationFile(FileNameInformation)
> also hangs.

Yeah, drat... but expected.

> > [FileProcessIdsUsingFileInformation]
> 
> Thanks for advice. get_query_hdl_per_* is called in the write side,
> so only knows pipe handle of the write side. We would like to know
> ProcessId which have pipe handle of the read side. Can we use
> FileProcessIdsUsingFileInformation for this perpose?

I don't know.  I just stumbled over it yesterday and I thought it might
be something we could utilize.  Supposedly it returns PIDs for processes
having that file open, but how this works for pipe read/write sides
needs testing.  Of course, knowing how Windows functions usually only go
half the way, the function will either only return the current side of
the pipe, or even an error code :-/  Never mind, it was just an idea.


Corinna


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