[PATCH v8] Cygwin: pipe: Switch pipe mode to blocking mode by default

[Takashi Yano]

On Mon, 28 Oct 2024 20:23:01 +0900
Takashi Yano wrote:
> Hi Corinna,
> 
> On Mon, 28 Oct 2024 10:55:31 +0100
> Corinna Vinschen wrote:
> > Hi Takashi,
> > 
> > On Oct 27 17:57, Takashi Yano wrote:
> > > Hi Corinna,
> > > 
> > > On Thu, 24 Oct 2024 12:21:04 +0200
> > > Corinna Vinschen wrote:
> > > > > > Before:
> > > > > > 
> > > > > >   $ ./x 40000
> > > > > >   pipe capacity: 65536
> > > > > >   write: writable 1, 40000 25536
> > > > > >   write: writable 1, 24576 960
> > > > > >   write: writable 0, 512 448
> > > > > >   write: writable 0, 256 192
> > > > > >   write: writable 0, 128 64
> > > > > >   write: writable 0, 64 0
> > > > > >   write: writable 0, -1 / Resource temporarily unavailable
> > > > > > 
> > > > > > After:
> > > > > > 
> > > > > >   $ ./x 40000
> > > > > >   pipe capacity: 65536
> > > > > >   write: writable 1, 40000 25536
> > > > > >   write: writable 1, 25536 0
> > > > > >   write: writable 0, -1 / Resource temporarily unavailable
> > > > > > 
> > > > > > This way, we get into the EAGAIN case much faster again, which was
> > > > > > one reason for 170e6badb621.
> > > > > > 
> > > > > > Does this make more sense, and if so, why?  If this is really the
> > > > > > way to go, the comment starting at line 634 (after applying your patch)
> > > > > > will have to be changed as well.
> > > > > 
> > > > > Perhaps, I did not understand intent of 170e6badb621. Could you please
> > > > > provide the test program (./x)? I will check my code.
> > > > 
> > > > I attached it.  If you call it with just the number of bytes per write,
> > > > e.g. `./x 12345', the writes are blocking.  If you add another parameter,
> > > > e.g. `./x 12345 1', the writes are nonblocking.
> > > 
> > > Thanks for the test case.
> > > I think I could restore the previous behaviour. Please try v9 patch.
> > > 
> > > CYGWIN_NT-10.0-19045 HP-Z230 3.5.4-1.x86_64 2024-08-25 16:52 UTC x86_64 Cygwin
> > > $ ./a.exe 40000 1
> > > pipe capacity: 65536
> > > write: writable 1, 40000 25536
> > > write: writable 1, 24576 960
> > > write: writable 0, -1 / Resource temporarily unavailable
> > > 
> > > Just after the commit 170e6badb621 (master branch)
> > 
> > Oops.  You tested in the wrong spot.  The original patch wasn't quite
> > polished, the followup patches 1ed909e047a2 and 686e46ce7148 are also
> > required to show the intended behaviour, and the intended behaviour is
> > the same in the blocking and non-blocking case...
> > 
> > > $ ./a.exe 40000 1
> > > pipe capacity: 65536
> > > write: writable 1, 40000 25536
> > > write: writable 1, 24576 960
> > > write: writable 0, -1 / Resource temporarily unavailable
> > 
> > So this should actually be:
> > 
> >   pipe capacity: 65536
> >   write: writable 1, 40000 25536
> >   write: writable 1, 24576 960
> >   write: writable 0, 512 448
> >   write: writable 0, 256 192
> >   write: writable 0, 128 64
> >   write: writable 0, 64 0
> >   write: writable 0, -1 / Resource temporarily unavailable
> > 
> > just as in the blocking case.
> 
> I have just tried commit 686e46ce714803f47d3183c954ceaf51976157cc,
> however the result is the same:
> CYGWIN_NT-10.0-19045 HP-Z230 3.6.0-dev-182-g686e46ce7148.x86_64 2024-10-28 11:17 UTC x86_64 Cygwin
> $ ./a.exe 40000 1
> pipe capacity: 65536
> write: writable 1, 40000 25536
> write: writable 1, 24576 960
> write: writable 0, -1 / Resource temporarily unavailable
> 
> What is wrong???

Is the test case I used different from yours? Without the 2nd arg,
$ ./a.exe 40000
pipe capacity: 65536
write: writable 1, 40000 25536
write: writable 1, SIGALRM 24576 960
write: writable 0, SIGALRM -1 / Interrupted system call

-- 
Takashi Yano <takashi.yano@nifty.ne.jp>