On 04-May-2001 Stanislav Malyshev a.k.a Frodo wrote:
>>> This is not a PROBLEM but a FEATURE. All Sys-V IPC (semaphores,
>>> message queues, shared memory) outlive their creators.
>
> Wrong. Shared memory can be pre-deleted, so that it is removed when last
> process is detached. Just like files.
True, but they can only be used by an already attached processes just like
open files that are unlinked (although they appear in ipcs(1), a shmget(2)
fails with 'identifier removed' error).
Actually, this was very interesting remark. Since the API's of the 3 Sys-V
IPC mechanisms is so similar I haven't noticed (until now) that shared
memory has different sematics (because it has shmdt() <==> close(), while
message queues and semaphores don't have an equivalent call).
Thanks for the enlightenment...
BTW: we both agree that for *mutual exclusion* there are better means than
semaphores.
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