GNU bug report logs - #72092
popen creates "/dev/null" fds and never closes them

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: jakub-w <at> riseup.net
To: bug-guile <at> gnu.org
Subject: popen creates "/dev/null" fds and never closes them
Date: Sat, 13 Jul 2024 12:07:52 +0000

Consider the following example:

(use-modules (ice-9 popen))

(parameterize ((current-error-port (%make-void-port OPEN_BOTH)))
  (while #t
    (close-pipe (open-pipe* OPEN_READ "free"))
    (sleep 1)))

This opens a new "/dev/null" file descriptor every second and doesn't
close it when close-pipe is called.
If current ports are all fd ports, this doesn't happen.

AFAICT the problem was introduced by the commit
36fd2b4920ae926c79b936c29e739e71a6dff2bc in Guile 3.0.10.

Message #8 received at 72092 <at> debbugs.gnu.org (full text, mbox):

From: nathan <nathan_mail <at> nborghese.com>
To: 72092 <at> debbugs.gnu.org, jakub-w <at> riseup.net
Subject: [PATCH] fix file descriptor leak in piped_process/system*/popen/etc
Date: Sat, 13 Jul 2024 18:22:58 +0000

[Message part 1 (text/plain, inline)]

fix is attached

test code:
(use-modules (ice-9 ftw))
(use-modules (ice-9 popen))
(define (print-open)
   (format #t "~a\n" (length (scandir "/proc/self/fd"))))
(let ((p (%make-void-port "rw")))
   (print-open)
   (parameterize ((current-output-port p) (current-input-port p) (current-error-port p))
     (system* "ls"))
   (close-port p)
   (print-open))
(parameterize ((current-error-port (%make-void-port OPEN_BOTH)))
     (while
      #t
      (close-pipe (open-pipe* OPEN_READ "free"))
      (print-open)
      (sleep 1)))

there's still a one-time increase in the file descriptors, but it seems unrelated. or at least much harder to find.

(by the way, ignoring current-output-port and using /dev/null is bad. it would be nice to open a pipe in that case and forward whatever the child writes to the scheme port.
but that would require a separate thread, and it may be impossible to do something like that for current-input-port)

[0001-fix-file-descriptor-leak-in-piped_process-system-pop.patch (text/x-patch, attachment)]

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