On 13 October 2012 16:38, Christopher Faylor wrote: > On Sat, Oct 06, 2012 at 05:48:44AM +0100, Andy Koppe wrote: >>On 25 September 2012 14:32, Ryan Johnson wrote: >>> On 25/09/2012 6:05 AM, Helmut Karlowski wrote: >>>> >>>> I type >>>> >>>> cat [some long ascii-file] >>>> >>>> then Ctrl-S (output stops), then Ctrl-Q (terminal hangs, can only be >>>> terminated by closing the window). >>>> >>>> Using minty 1.1.2 and 1.7.16(0.262/5/3) 2012-07-20 22:55 i686 Cygwin >>>> >>>> Can anybody reproduce this? >>>> >>> Confirmed with mintty 1.1.1 and the same version of cygwin (w7-64). FWIW, >>> doing it with `find .' rather than `cat' works fine. >> >>The issue isn't specific to any of mintty, cat or Ctrl+S; for example, >>I've managed to reproduce it with xterm, hexdump, and just hitting >>Enter. Any other key that sends a keycode will do too. Ctrl+Q isn't >>needed for the freeze to happen. In xterm I've even managed it with >>find, by hitting Enter repeatedly. >> >>If you then look at the situation in ps, you'll see something like this: >> >>O 3396 1 3396 1472 ? 1004 05:11:07 /usr/bin/xterm >>O 3528 4460 3528 528 pty3 1004 05:25:01 /usr/bin/cat >> >>The interesting bit there is the two 'O's in the first column, which >>means both processes are waiting to output. I think what's happening >>is that both of them are trying to write to their side of the >>underlying pty device, but that those writes are blocking until data >>is read from the other side of the pty. Result: deadlock. If the cat >>is killed (possibly with -9, because of its nine lives), the terminal >>happily continues on its way. >> >>So why doesn't this happen more often? Not sure. The speed difference >>between the client process output and the terminal seems to play a >>role here. I can only guess that the issue occurs if a buffer in the >>pty's slave->master pipe overflows and something is written to the >>master->slave pipe at the same time (which is unbuffered?). >> >>I don't understand the pty implementation enough to verify any of >>that, so cgf would need to comment further. Note besides: I couldn't >>make this deadlock happen on Ubuntu. > > This should work in the latest snapshot. I added a polling kludge for > 1.7.17 while I mull over the best way to handle this.
Using snapshot 2012-10-16, I confirmed that Ctrl+S during a long cat no longer freezes the terminal and that Ctrl+Q However, I still see the deadlock described above when hitting any other key that sends something, e.g. just Enter. Andy -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
