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

[Corinna Vinschen <corinna-cygwin@cygwin.com>]

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:
> > > > I tried to implement your idea, however, I noticed that
> > > > NtQueryObject(ObjectNameInformation) call in
> > > > get_query_hdl_per_process() is blocked while reading the
> > > > pipe if FIPE_SYNCHRONOUS_IO_NONALERT is set and pipe is
> > > > in blocking mode.
> > > > 
> > > > 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?
> > > 
> > > Can you push this to the topic/pipe branch for playing?  I updated
> > > the branch to current master.
> > 
> > Thanks. I have just pushed the experimental patch to topic/pipe.
> > Please try. If something wrong, please point it out.
> 
> Great, I'll have a look.  Ken, you're looking as well, right?

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?  

Btw., while looking I was wondering if get_query_hdl_per_process and
get_query_hdl_per_system could be replaced by a function utilizing
NtQueryInformationFile(FileProcessIdsUsingFileInformation).  This
supposedly returns all process ids of processes having an open handle to
this file.  This could be quite a bit faster than the other two
functions, ideally.  Per MSDN, FileProcessIdsUsingFileInformation
exists since Vista.


Corinna