Hi Ken, On Sat, 28 Aug 2021 16:55:52 -0400 Ken Brown wrote: > On 8/28/2021 11:43 AM, Takashi Yano via Cygwin wrote: > > On Sat, 28 Aug 2021 13:58:08 +0200 > > Corinna Vinschen wrote: > >> On Aug 28 18:41, Takashi Yano via Cygwin wrote: > >>> On Sat, 28 Aug 2021 10:43:27 +0200 > >>> Corinna Vinschen wrote: > >>>> On Aug 28 02:21, Takashi Yano via Cygwin wrote: > >>>>> On Fri, 27 Aug 2021 12:00:50 -0400 > >>>>> Ken Brown wrote: > >>>>>> Two years ago I thought I needed nt_create to avoid problems when > >>>>>> calling > >>>>>> set_pipe_non_blocking. Are you saying that's not an issue? Is > >>>>>> set_pipe_non_blocking unnecessary? Is that the point of your > >>>>>> modification to > >>>>>> raw_read? > >>>>> > >>>>> Yes. Instead of making windows read function itself non-blocking, > >>>>> it is possible to check if the pipe can be read before read using > >>>>> PeekNamedPipe(). If the pipe cannot be read right now, EAGAIN is > >>>>> returned. > >>>> > >>>> The problem is this: > >>>> > >>>> if (PeekNamedPipe()) > >>>> ReadFile(blocking); > >>>> > >>>> is not atomic. I. e., if PeekNamedPipe succeeds, nothing keeps another > >>>> thread from draining the pipe between the PeekNamedPipe and the ReadFile > >>>> call. And as soon as ReadFile runs, it hangs indefinitely and we can't > >>>> stop it via a signal. > >>> > >>> Hmm, you are right. Mutex guard seems to be necessary like pty code > >>> if we go this way. > >>> > >>>> Is a blocking ReadFile actually faster than a non-blocking read? Or > >>>> does it mainly depend on BYTE vs. MESSAGE mode? > >>> > >>> Actually, I don't think so. Perhaps it is not essential problem of > >>> overlapped I/O but something is wrong with current pipe code. > >>> > >>>> What if the pipe is created non-blocking and stays non-blocking all the > >>>> time and uses BYTE mode all the time? Just as sockets, it would always > >>>> only emulate blocking mode. Wouldn't that drop code size a lot and fix > >>>> most problems? > >>> > >>> If 'non-blocking' means overlapped I/O, only the problem will be: > >>> https://cygwin.com/pipermail/cygwin/2021-March/247987.html > >> > >> Sorry if that wasn't clear, but I was not talking about overlapped I/O, > >> which we should get rid off, but of real non-blocking mode, which > >> Windows pipes are fortunately capable of. > > > > Do you mean, PIPE_NOWAIT flag? If this flags is specified in > > the read pipe, non-cygwin apps cannot read the pipe correctly. > > While waiting for Corinna's response to this, I have one more question. Do > you > understand why nt_create() failed and you had to revert to create()? Was it > an > access problem because nt_create requested FILE_WRITE_ATTRIBUTES? Or did I > make > some careless mistake in writing nt_create?
I am sorry but no. I don't understand why piping C# program via the pipe created by nt_create() has the issue. I tried to change setup parameters in nt_create(), however, I did not succeed it to work. I also couldn't find any mistake in nt_create() so far. Win32 programs which use ReadFile() and WriteFile() work even with the pipe created by nt_create() as well as overlapped I/O. What does C# program differ from legacy win32 program at all? -- Takashi Yano <takashi.y...@nifty.ne.jp> -- Problem reports: https://cygwin.com/problems.html FAQ: https://cygwin.com/faq/ Documentation: https://cygwin.com/docs.html Unsubscribe info: https://cygwin.com/ml/#unsubscribe-simple
