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

Corinna Vinschen corinna-cygwin@cygwin.com
Wed Nov 10 10:34:25 GMT 2021


On Nov 10 17:30, Takashi Yano wrote:
> Hi Corinna,
> 
> On Sat, 6 Nov 2021 12:42:46 +0100
> Corinna Vinschen wrote:
> > On Nov  6 15:10, Takashi Yano wrote:
> > > Unfortunately, these solutions do not resolve the issue
> > > which is another issue with C# program:
> > > https://cygwin.com/pipermail/cygwin/2021-March/247987.html
> > > This still needs FILE_SYNCHRONOUS_IO_NONALERT flag.
> > 
> > If we want to add FILE_SYNCHRONOUS_IO_NONALERT, this would have to be
> > solved by running NtReadFile/NtWriteFile synchronously in a thread,
> > started on every invocation of raw_read/raw_write.  raw_read/raw_write
> > would then call cygwait on the thread object.  To break on signal or
> > thread cancallation events, it would have to call CancelSynchronousIo.
> > That's certainly doable.
> 
> 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,
Corinna


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