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Re: Posix Inter-process comunication on RH 7.1
- To: Shaul Karl <shaulka(at-nospam)bezeqint.net>
- Subject: Re: Posix Inter-process comunication on RH 7.1
- From: guy keren <choo(at-nospam)actcom.co.il>
- Date: Thu, 25 Oct 2001 09:55:25 +0200 (EET)
- cc: Gold Edward <avieal(at-nospam)inter.net.il>, <linux-il(at-nospam)linux.org.il>
- Delivered-To: linux.org.il-linux-il@linux.org.il
- In-Reply-To: <E15wWd9-0000UT-00@rakefet>
- Sender: linux-il-bounce(at-nospam)cs.huji.ac.il
On Thu, 25 Oct 2001, Shaul Karl wrote:
> You sounds to me very negative to system V IPC. Why is that?
for both practical and historic reasons.
1. sys V IPC _seems_ to be the feature that first broge (on large scale)
the 'everything is a file' metaphore. you cannot select() on sys V
queues or semaphores, for the simple reason that they do not have a
file descriptor.
2. because of the above, using sys V IPC together with other mechanisms
often requiers creatig threads (and adding complexity) that you don't
want to use. think of a program that needs to work with a socket (for
networking) and wishes to use a sys V message queue for its IPC
(a multi-process mail server, for example, if one truly existed).
3. in sysV message queues, the limit on queue size is system-wide, not
per-process, per-queue or per-user. this can cause one heck of a
problem if one program that uses them goes amock.
4. sys V queues and semaphores that interact between processes may exceed
the lives of the processes that created them. thus, you need to perform
various system managemend tasks (e.g. in case of software crash).
5. keys used to name resources aren't easily uniquely assigned, and
require you to use some 'black-magic', and hope not to land on some
race (i.e. man ftok, and then see that the key it generates is based on
inode numbers in a fiel system - what if another process used ftok on
another file system, and happened to land on the same inode number?)
btw, i don't know if similar problems do not exist with posix IPC - i
never bothered reading too much about it, because it wasn't portable
enough for my wishes.
--
guy
"For world domination - press 1,
or dial 0, and please hold, for the creator." -- nob o. dy
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