I finally figured out why autoconf is still failing its flock-related tests,
and why perl was reliably failing even though my simple attempts in C were
always passing. It turns out that if you do:
open
flock(LOCK_EX)
if (!fork)
execlp("sleep","sleep","10",NULL);
sleep(10);
then ProcessExplorer shows that the Event in the global namespace of flock-dev-
ino\20-2-* exists in both parent and child, and with a notification level of
false, blocking any outside influence until both the parent and forkee exit.
But if you do:
open
fcntl (fd, F_SETFD, FD_CLOEXEC | fcntl (fd, F_GETFD))
flock(LOCK_EX)
if (!fork)
execlp("sleep","sleep","10",NULL);
sleep(10);
then only the parent holds a handle to the Event, but with a notification level
of true, allowing any outside party to do whatever they want.
I'm still trying to figure out why the close-on-exec cleanup appears to be
spuriously triggering the flock Event to unlock. But my understanding is that
F_FLOCK locks should survive over exec, so the close-on-exec cleanup should
only trigger lock release on F_POSIX locks.
--
Eric Blake
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