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 -- 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
