Formal comment #186 (defect)

Buffer mode should be specifiable on open-file-input-port
Reported by: 	John Cowan
Version:	5.92

Currently, buffer modes are for output only. However, operating
systems also distinguish between buffered and unbuffered input. The
open-file-input-port procedure should be allowed to accept an
additional argument specifying the buffer mode, in parallel with
open-file-output-port. Allowing input to be unbuffered can limit
deadlocks when dealing with communicating processes.


RESPONSE:

The next draft will adopt this recommendation.

If two ports are connected to the same mutable source,
and both ports are unbuffered, and reading a byte or
character from that shared source via one of the two
ports would change the bytes or characters seen via
the other port, then peeking (or lookahead) on one port
will render the peeked byte or character inaccessible
via the other port, while a subsequent read (or get)
on the peeked port will see the peeked byte or character
even though the port is otherwise unbuffered.

In other words, the semantics of buffering is defined
in terms of side effects on shared mutable sources,
and a peek or lookahead operation has the same side
effect on the shared source as a read or get.