Re: [PATCH v3 1/2] add interface for /dev/tty interaction

Jeff King [off-list ref] writes:

Erik has looked into doing a Windows alternative in compat/terminal.c,
and I think an integer would be insufficient there. In particular, I
think Windows needs two descriptors to accomplish the same thing (one
for CONIN$ and one for CONOUT$).  So you'd need to turn term_t into a
struct (and you'd probably not want to return it by value then).

Maybe it would be better to keep the abstraction as non-leaky as
possible, and just provide "terminal_can_prompt()" or similar?

OK.  As we won't be giving separate instances of terminals to
different callers anyway, compat/terminal.c can keep a static
variable of whatever type that is necessary for the implementation
around.  That sounds like a reasonable way to go.

Returning the open descriptor (as Tay's patch does) avoids a race
condition where /dev/tty can be opened when terminal_can_prompt runs,
but not when we try to actually read from it. But we can either:

  1. Not care. Even if the tty is opened, if a user has closed the
     terminal we are going to get a read error anyway. So you can never
     avoid that race condition in some form.

  2. Open the terminal descriptor when either function is called, and
     never close it. I don't think there is any reason we can't just
     leak the descriptor.

-Peff