[Openmcl-devel] Bug in concatenated-stream implementation

[Stas Boukarev]

Which would violate the standard, as "The effect of close on a constructed
stream is to close the argument stream only. There is no effect on the
constituents of composite streams."

On Thu, Mar 16, 2017 at 3:54 PM, Paul Meurer <paul.meurer at uni.no> wrote:

> Hello,
>
> there seems to be a bug in the concatenated-stream class in connection
> with with-open-stream().
>
> When a concatenated-stream is read from in the body of the macro, (e.g.
> with read-sequence()), concatenated-stream-next-input-stream() is called
> subsequently, which removes the first stream from the
> concatenated-stream-streams slot, eventually emptying this slot.
>
> In its unwind-protect cleanup-form, with-open-stream() should close the
> stream, but there is no close method for concatenated-stream. (The
> superclass method on composite-stream-mixin just sets open-p to NIL.) With
> the concatenated-stream-streams slot being empty after an exhaustive read
> with e.g. read-sequence(), there is no obvious way either how the stream
> could be closed. The best way to solve this problem would probably be to
> have a copy of the stream list in an additional slot, and have close map
> over them when closing the concatenated-stream.
>
> This bug manifests itself e.g. in the mel-base library.
>
> My fix (in l1-streams.lisp) looks like this:
>
> (defclass concatenated-stream (composite-stream-mixin
> fundamental-input-stream)
>     ((streams :initarg :streams :accessor concatenated-stream-streams)
>      (stream-list :initarg :stream-list :accessor
> concatenated-stream-stream-list)))
>
> (defmethod close :after ((stream concatenated-stream) &key abort)
>   (mapc (lambda (s) (close s :abort abort))
>         (concatenated-stream-stream-list stream)))
>
> (defun make-concatenated-stream (&rest streams)
>   "Return a stream which takes its input from each of the streams in turn,
>    going on to the next at EOF."
>   (dolist (s streams (make-instance 'concatenated-stream :streams streams
> :stream-list streams))
>     (unless (input-stream-p s)
>       (error "~S is not an input stream" s))))
>
>
> Paul Meurer
>
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>



-- 
With best regards, Stas.
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