Category Archives: Uncategorized

SBCL: Testsuites Cannot Prevent All Possible Bugs

On OS X, SBCL as of 1.3.14 can’t sleep after fork. The following simple program exits with an error.

(require 'sb-posix)

(let ((pid (sb-posix:fork)))
  (if (= 0 pid)
        (format t "Child: Sleeping for 10 seconds.~%")
        (sleep 10)
        (format t "Child: I woke up.~%"))
    (format t "Parent, exiting.~%")))

When the above script is run on OS X, it fails with the weird error we see below. Note that it works perfectly on Linux.

% sbcl --script
Parent, exiting.
Child: Sleeping for 10 seconds.
fatal error encountered in SBCL pid 16145:
(ipc/send) invalid destination port

The point of this, is that there is no reasonable way a testsuite will catch this kind of a bug. Testsuites, no matter how comprehensive, will never prevent bugs 100%. At most, they prevent the same bug from reappearing.

Hopefully the SBCL team will fix this bug soon.