On Aug 29 00:43, 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.
Do you mean after execve? If the child is a non-Cygwin process, we could run a loop over the stdio descriptors in child_info_spawn::worker setting pipes to blocking. But that's a corner problem, easily solved. It's more important that it works nicely for Cygwin processes. Corinna -- 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
