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SubjectRe: directory notifications lost after fork?
(Manually quoted from the archive)

> Just a "me too".
> I have tried also to use the default (SIGIO) by setting owner pid (just
> in case). It is all the same.
> Does someone use the notifications, btw?
> The whole thing seems somewhat untested.
> -alex
We used to use them in the KDE libraries. However, we decided to disable it
for now due to this problem since it's not theoretical, it hits quite often
in konqueror and especially kdesktop as both spawn child processes.
On a side note, dnotify is pretty weak compared to FAM with imon
Imagine a file manager that has a view on a large directory like /usr/bin. Now
a file in that directory is added / removed / changed. With dnotify, the
filemanager will have to rescan the whole directory as a reaction to the
signal, to find out which file has changed. OTOH, with FAM, it gets a precise
event that tells "file `somebinary' has been added" or similar.
I don't have much of a clue about the kernel, so please excuse my ignorance,
but the imon patch seems pretty unintrusive to me and enables more
fine-grained file change notifications than dnotify. Also, FAM can monitor
NFS-mounted directories with almost no network overhead when it's also
running on the server.

> On Sun, Mar 10, 2002 at 10:08:02PM +0100, Oskar Liljeblad wrote:
> > The code snipper demonstrates what I consider a bug in the
> > dnotify facilities in the kernel. After a fork, all registered
> > notifications are lost in the process where they originally
> > where registered (the parent process). "lost" here means that
> > the signal specified with F_SETSIG fcntl no longer is delivered
> > when notified.


PS: I'm not subscribed, please CC me on answers; I'll also watch the archive.
Malte Starostik
PGP: 1024D/D2F3C787 [C138 2121 FAF3 410A 1C2A 27CD 5431 7745 D2F3 C787]

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