On Fri, Oct 19, 2012 at 02:17:29PM +0200, Corinna Vinschen wrote: >On Oct 19 12:26, Andy Koppe wrote: >> On 13 October 2012 16:38, Christopher Faylor wrote: >> > On Sat, Oct 06, 2012 at 05:48:44AM +0100, Andy Koppe wrote: >> >>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. > >Too bad. Are you sure? I tried really hard to get a deadlock and could >not reproduce it anymore under W7. My Enter key is still on paracetamol.
I can't duplicate it either. I do notice that Cygwin doesn't work like UNIX in that characters are still echoed after CTRL-S is hit. That's wrong but it looks like making it right will require major surgery. Must. Resist. YA. Pty. Rewrite. cgf -- 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
