fd-closing finalizer on streams considered unwarranted

[Tobias C. Rittweiler]

OPEN passes :AUTO-CLOSE T to MAKE-FD-STREAM, resulting in the creation
of a finalizer for the stream which closes the underlying file descriptor in case
it has not when the stream will be garbaged collected.

I think that is not a good thing to do (by default anyway) because it postpones
fd leakage problems, and makes them harder to track down.

[Gábor Melis (melisgl)]

Sounds reasonable to me. Maybe the finalizer could warn though or
print a message as it does with #!+sb-show.

[Tobias C. Rittweiler (tcr)]

I'd think :AUTO-CLOSE should be keyword parameter of OPEN, defaulting to
*STREAM-AUTO-CLOSE-BEHAVIOUR* which is NIL by default, but
can also be T, :WARN, and :ERROR.

[James Y Knight (foom)]

Wait, what? You think it should keep the FD open forever instead? Sounds like a terrible idea.

It sounds like you're asking for debugging assistance; it seems to me that all you really need is for the lambda to become a named function so you can call 'trace' on it.

[Stig Hemmer (stighemmer)]

It seems to me that AUTO-CLOSE doesn't postpone fd leakage problems, but solves them.

[Paul Khuong (pvk)]

It only solves them by accident, if the application triggers full-enough GCs at the right frequency.

[Tobias C. Rittweiler (tcr)]

James: What lambda?

[James Y Knight (foom)]

Sorry: the finalizer's:

    (when (and auto-close (fboundp 'finalize))
      (finalize stream
                (lambda ()
                  (sb!unix:unix-close fd)
                  #!+sb-show
                  (format *terminal-io* "** closed file descriptor ~W **~%"
                          fd))
                :dont-save t))

I meant, if it was something like this:

(defun finalize-close-fd (fd)
  (sb!unix:unix-close fd)
  #!+sb-show
  (format *terminal-io* "** closed file descriptor ~W **~%"
          fd))
[...]
      (finalize stream
                (lambda ()
                  (finalize-close-fd fd))
                :dont-save t))

You could easily do (trace sb-impl::finalize-close-fd :break t).

[Nikodemus Siivola (nikodemus)]

I agree that it should be easier to debug such potential FD leaks, however this is exactly implemented.