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Re: cygipc-1.11 SHM-patch: fork, handling in ipc-daemon
- From: Michael Haubenwallner <michael dot haubenwallner at salomon dot at>
- To: Robert Collins <robert dot collins at itdomain dot com dot au>
- Cc: Charles Wilson <cwilson at ece dot gatech dot edu>, cygwin at cygwin dot com
- Date: Mon, 21 Jan 2002 09:57:16 +0100
- Subject: Re: cygipc-1.11 SHM-patch: fork, handling in ipc-daemon
- References: <3C482133.E3C673D2@salomon.at> <0a9801c1a079$4dd50e60$0200a8c0@lifelesswks>
Robert Collins wrote:
>
> ===
> ----- Original Message -----
> From: "Michael Haubenwallner" <michael.haubenwallner@salomon.at>
> > - It is not clear what happens in following circumstance:
> > 1) the first process creates a shm
> > 2) a second one attaches to it
> > 3) now the second process dies without detaching
> > 4) the first process removes the shm with shmctl(IPC_RMID),
> > but the ipc-daemon was sleeping and did not remove the
> > second attachment-entry early enough to have shm_nattch==0,
> > which must be the case in shmctl() to really remove the shm
> > by the caller of shmctl(IPC_RMID).
> >
> > What IMHO surely not should happen is that a shmid with
> > shm_nattch==0 remains with having the destroy-flag set.
> > So the ipc-daemon must remove a shm in this state,
> > including the tmp-file.
>
> In this case, the daemon should wait on all the processes that are
> attached, so it gets woken up when a process quits. Alternatively, you
> could queue the removal, prevent now attachments, and when the second
> process termination is 'noticed' perform the removal.
>
> Rob
I forgot to say that the removal _is_ done with this patch by the
daemon when the second process (meaning the last attached process)
terminates, which is the 'alternative' way in your description.
haubi
--
Michael Haubenwallner SALOMON Automation GmbH
Forschung & Entwicklung A-8114 Friesach bei Graz
mailto:michael.haubenwallner@salomon.at http://www.salomon.at
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