[PATCH] Cygwin: console: Change timing of set/unset xterm compatible mode.

[Corinna Vinschen]

On Feb 17 10:00, Corinna Vinschen wrote:
> Hi Takashi,
> 
> On Feb 16 17:13, Takashi Yano wrote:
> > - If two cygwin programs are executed simultaneousley with pipes
> >   in cmd.exe, xterm compatible mode is accidentally disabled by
> >   the process which ends first. After that, escape sequences are
> >   not handled correctly in the other app. This is the problem 2
> >   reported in https://cygwin.com/ml/cygwin/2020-02/msg00116.html.
> >   This patch fixes the issue. This patch also fixes the problem 3.
> >   For these issues, the timing of setting and unsetting xterm
> >   compatible mode is changed. For read, xterm compatible mode is
> >   enabled only within read() or select() functions. For write, it
> >   is enabled every time write() is called, and restored on close().
> 
> Oh well, I was just going to release 3.1.3 :}
> 
> In terms of this patch, rather than to change the mode on every
> invocation of read/write/select/close, wouldn't it make more sense to
> count the number of mode switches in a shared per-console variable, i.e.
> 
> LONG shared_console_info::xterms_mode = 0;
> 
> on open:
> 
>   if (InterlockedIncrement (&xterm_mode) == 1)
>     switch to xterm mode;
> 
> on close:
> 
>   if (InterlockedDecrement (&xterm_mode)) == 0)
>     switch back to compat mode;
> 
> ?

On second thought, also consider that switching the mode and
reading/writing is not atomic.  You'd either have to add locking, or you
may suffer the same problem on unfortunate task switching.


Corinna

-- 
Corinna Vinschen
Cygwin Maintainer
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