Subject: Re: cygipc-1.11 SHM-patch: fork, handling in ipc-daemon
From: "Robert Collins" <[email-masked]>
To: "Michael Haubenwallner" <[email-masked]>, "Charles Wilson" <[email-masked]>
Cc: <[email-masked]>
Date: Sat, 19 Jan 2002 10:38:58 +1100

===
----- Original Message -----
From: "Michael Haubenwallner" <[email-masked]>
> - 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

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