On Wed, May 11, 2011 at 11:02:40AM -0400, Edward Lam wrote: >On 5/11/2011 2:34 AM, Corinna Vinschen wrote: >> Kind of weird. The difference is that in tty mode the stdio handles are >> pipes, while in the notty case the stdio handles are console handles. >> Usually native Windows applications shouldn't see a difference and even >> work *better* in notty mode. > >One problem I ran into was with *Windows mode* applications (ie. MS >link.exe option /SUBSYSTEM:windows) trying to detect stdout redirection. >I apologize that this takes a bit of explaining first as to why we run >into a problem with Cygwin. > >For Windows-mode applications, _isatty(_fileno(stdout)) will always >return false. Due to a bug (in Windows and/or the CRT), the FILE *stdout >object will be initialized to a black hole. So if you want printf's to >make its way into the redirected file, you have to manually connect the >FILE *stdout object to the redirected file output handle. > >The usual method is to call GetStartupInfo(&info) and check if >info.dwFlags has the STARTF_USESTDHANDLES flag set. If it is set, then >assume that info.hStdOutput contains the redirected file output handle >and attach it with something like: > *stdout = _fdopen(_open_osfhandle(info.hStdOutput, _O_TEXT)); > >So this brings us to Cygwin. When we spawn such a Windows mode app from >Cygwin, the method I describe above fails. The call to >_open_osfhandle(info.hStdOutput, _O_TEXT) returns with an error value of >-1. This is likely why jam reports "the handle is invalid". > >Personally, when I first ran into this problem, I never realized that >CYGWIN=tty would fix it. I did notice that there was a change in the >behavior between Cygwin B20 and the Cygwin 1.X releases but I only >realize now that this was probably the reason.
Just to go on mean record: I don't think the fact that jam works better as side effect of setting CYGWIN=tty is a good enough reason to derail any plans to get rid of CYGWIN=tty. It seems like you might be able to get the same behavior by saying jam </dev/null 2>&1 | cat 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
