Groups > comp.lang.java.programmer > #21090

Re: single instance

From	Twirlip of the Mists <twirlip@killfile.me.now.invalid>
Newsgroups	comp.lang.java.programmer
Subject	Re: single instance
Date	2013-01-06 20:04 -0500
Organization	Zamps Anonymous
Message-ID	<kcd6va$c9a$1@news.mixmin.net> (permalink)
References	(3 earlier) <kc4rpu$4at$1@localhost.localdomain> <PNidnQgKw5vavHXNnZ2dnUVZ8t-dnZ2d@bt.com> <kc9onj$bp9$1@localhost.localdomain> <kc9psj$5k0$1@news.mixmin.net> <kca2g0$gsb$1@localhost.localdomain>

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On Sat, 5 Jan 2013 20:29:52 +0000 (UTC), Martin Gregorie wrote:

> On Sat, 05 Jan 2013 13:02:57 -0500, Twirlip of the Mists wrote:
> 
>> C's atexit is probably vulnerable to the latter two, mitigatable only
>> partially by registering signal handlers.
>>
> I don't think any of these approaches are immune to system crashes, but 
> should be good enough to prevent single processes, whether launched by a 
> user or automatically by the system, from running more copies that are 
> wanted.

As I concluded at the end of my post.

> I'd normally use a shell script or programmed equivalent to launch a more 
> complex set of processes. Its first action would be to assume a crash had 
> ocurred and do a full clean-up: if the system had shut down normally the 
> clean-up would still run but would not find anything to do.

That may make sense for a lot of systems.

>> The only thing I can think of that even the thunderstorm won't fuck up
>> is an active system where the lockfile is only considered valid if some
>> associated "heartbeat" is still going, so, the lockfile invalidates on a
>> deadman switch even if not deleted.
>>
> Yes, that would work too: though it sounds as if the mere existence of a 
> small 'heartbeat' process could obviate the need for a lockfile:

Uh, something still has to point to the location of the heartbeat process.
Either that needs a fixed but configurable port, or else the lockfile (or
some sort of file, anyway) is needed (itself in a fixed location) to point
to the port-du-jour.

> if the heartbeat process is running and agrees that the limit for your
> process type hasn't been reached, your process can start.

"The limit for your process type"? That doesn't sound like you're thinking
of an app that should, by default, run as a single instance that "absorbs"
any more that the user triggers by e.g. double-clicking documents, more for
efficiency reasons or to avoid race conditions with its data files than for
any other reason. It sounds more like you're thinking of a situation
involving enforcing policy against users for reasons that have nothing to
do with those users' own wishes, say to limit their resource consumption on
a work computer that isn't theirs.

That's a whole different kettle of fish, but it's a kettle of fish best
handled at the OS level much of the time:

* The resource use at the guy's own cubicle box is his own business. If he
  squanders it and then can't get his work done, he can be let go for poor
  productivity or whatever.

* The resource use on shared machines, e.g. a network server supplying
  services to a whole office block, can be managed by that machine's OS
  having per-user quotas set up, if the users have accounts on it, or by
  the server software enforcing quotas. The latter is similar to how a
  publicly-exposed web service without authentication might prevent one
  user hogging too many resources -- per-connecting-IP resource quotas past
  which it slows down or times out, intentional latency high enough to
  limit the damage a rampaging bot client can do from rapid-fire sequential
  requests but low enough not to nuisance a human user with human reaction
  times, etc.
  Some situations likely in the wild 'net are much less so on the company
  LAN, of course, such as the rampaging bot. And, if something that
  egregious ever does occur, whoever's responsible can be fired.

In a workplace environment, with software customized for that particular
workplace, you can generally go much further in deciding things that users
should and should not do than with software intended for a general audience
including people running it on their own hardware with their own time and
paying their own utility bills.

Even then, it's often better to audit rather than strictly ration use, and
then hold employees accountable for unnecessary and excessive usage based
on the audit reports. Of all the different kinds of bureaucratic red tape
out there, the machine-enforced variety is easily the worst, because it's
typically *impossible* to circumvent without going through the proper
channels, even in direst emergency with some sort of looming deadline and,
with characteristically bad timing, the pointy-haired single point of
failure that holds the needed pad of permission slips home sick. In all
other situations, "contrition is easier than permission" should be a
possible approach, on pain of losing your job if your corner-cutting was
frivolous rather than out of good faith perceived necessity. Though it
certainly should not be the default.

(Of course, because machine-enforced red tape *is* so hard to circumvent,
the bureaucrats *really* love it...)

Another thing to note is that all of the possibly-limited computing
resources -- CPU, disk, memory, bandwidth -- are so cheap these days that a
company can easily afford to have internal servers with 10x or more
capacity than the likely peak load from normal employee use of its
services, such that it would take truly exceptional circumstances (a 10x
bigger than normal demand, or deliberate bad faith or a major malware
infestation) for it to be unable to meet demand. The result is that the
cost in enforcing quotas (or even in auditing usage, possibly) could
actually exceed the benefit (the cost in enforcing has to factor in the
eventuality of someone legitimately needing more than their quota, and the
relevant permission slip being slow or difficult to obtain, with a
deadline; and the cost of both has to factor in the added system complexity
and accompanying bugs; bugs in enforcement are quite likely to result in
people being locked out of the system that are *under* quota, since half of
errors can be expected to be in that direction).

The other limited resource is money, to pay for electricity and (external)
bandwidth whose use may go up. But with efficient hardware an employee
would have to cause very big jumps in server loads to cost noticeable
amounts of marginal hydro-bill dollars, and the firewall can work both ways
to make excessive use of external bandwidth unlikely. Business connections
tend to be non-metered anyway, so while congestion can be a problem overuse
won't directly cost money. (It might indirectly do so, if
revenue-generating public-facing services are knocked out. Those should
probably be on a separate pipe from the one feeding the offices' internet
connectivity, routed differently enough that congesting one won't impair
the other. That's equally important in reverse, so if the web server's
under a DDoS or unusually high legitimate demand it won't cripple the
office workers that need to deal with the problem by cutting them off from
email, Wikipedia, Google, et. al.)

-- 
Hexapodia is the key insight.

Thread

single instance Roedy Green <see_website@mindprod.com.invalid> - 2013-01-01 12:23 -0800
  Re: single instance Arne Vajhøj <arne@vajhoej.dk> - 2013-01-01 16:40 -0500
    Re: single instance Robert Tomsick <robert+usenet@tomsick.net> - 2013-01-03 01:20 -0500
  Re: single instance Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2013-01-03 00:55 -0800
    Re: single instance Knute Johnson <nospam@knutejohnson.com> - 2013-01-03 19:31 -0800
      Re: single instance Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2013-01-03 19:49 -0800
      Re: single instance Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2013-01-03 19:56 -0800
        Re: single instance Twirlip of the Mists <twirlip@killfile.me.now.invalid> - 2013-01-04 12:18 -0500
          Re: single instance Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2013-01-04 10:22 -0800
            Re: single instance Twirlip of the Mists <twirlip@killfile.me.now.invalid> - 2013-01-04 13:44 -0500
              Re: single instance Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2013-01-04 11:03 -0800
                Re: single instance Twirlip of the Mists <twirlip@killfile.me.now.invalid> - 2013-01-04 14:12 -0500
              Re: single instance Arne Vajhøj <arne@vajhoej.dk> - 2013-01-05 21:56 -0500
                Re: single instance Twirlip of the Mists <twirlip@killfile.me.now.invalid> - 2013-01-06 19:22 -0500
                Re: single instance Arne Vajhøj <arne@vajhoej.dk> - 2013-01-06 20:23 -0500
                Re: single instance Twirlip of the Mists <twirlip@killfile.me.now.invalid> - 2013-01-06 20:43 -0500
                Re: single instance Arne Vajhøj <arne@vajhoej.dk> - 2013-01-06 20:47 -0500
                Re: single instance Twirlip of the Mists <twirlip@killfile.me.now.invalid> - 2013-01-06 20:51 -0500
                Re: single instance Arne Vajhøj <arne@vajhoej.dk> - 2013-01-06 20:24 -0500
                Re: single instance Twirlip of the Mists <twirlip@killfile.me.now.invalid> - 2013-01-06 20:46 -0500
                Re: single instance Arne Vajhøj <arne@vajhoej.dk> - 2013-01-06 20:58 -0500
                Re: single instance Twirlip of the Mists <twirlip@killfile.me.now.invalid> - 2013-01-06 21:08 -0500
                Re: single instance Arne Vajhøj <arne@vajhoej.dk> - 2013-01-06 21:19 -0500
                Re: single instance Twirlip of the Mists <twirlip@killfile.me.now.invalid> - 2013-01-06 21:31 -0500
                Re: single instance Arne Vajhøj <arne@vajhoej.dk> - 2013-01-06 21:41 -0500
                Re: single instance Twirlip of the Mists <twirlip@killfile.me.now.invalid> - 2013-01-06 22:00 -0500
                Re: single instance Arne Vajhøj <arne@vajhoej.dk> - 2013-01-06 22:11 -0500
                Re: single instance Twirlip of the Mists <twirlip@killfile.me.now.invalid> - 2013-01-07 00:23 -0500
                Re: single instance Arne Vajhøj <arne@vajhoej.dk> - 2013-02-24 18:20 -0500
                Re: single instance Joshua Cranmer <Pidgeot18@verizon.invalid> - 2013-01-06 21:39 -0600
                Re: single instance Twirlip of the Mists <twirlip@killfile.me.now.invalid> - 2013-01-07 00:30 -0500
                Re: single instance lipska the kat <lipskathekat@yahoo.co.uk> - 2013-01-07 08:53 +0000
                Re: single instance Arne Vajhøj <arne@vajhoej.dk> - 2013-02-24 18:18 -0500
                Re: single instance lipska the kat <"nospam at neversurrender dot co dot uk"> - 2013-02-25 08:31 +0000
                Re: single instance Arne Vajhøj <arne@vajhoej.dk> - 2013-02-24 18:17 -0500
                Re: single instance Lew <lewbloch@gmail.com> - 2013-01-06 17:32 -0800
                Re: single instance Twirlip of the Mists <twirlip@killfile.me.now.invalid> - 2013-01-06 20:47 -0500
                Re: single instance Arne Vajhøj <arne@vajhoej.dk> - 2013-01-06 20:53 -0500
                Re: single instance Twirlip of the Mists <twirlip@killfile.me.now.invalid> - 2013-01-06 21:01 -0500
          Re: single instance Arne Vajhøj <arne@vajhoej.dk> - 2013-01-05 21:59 -0500
            Re: single instance Twirlip of the Mists <twirlip@killfile.me.now.invalid> - 2013-01-06 19:34 -0500
              Re: single instance Arne Vajhøj <arne@vajhoej.dk> - 2013-01-06 20:00 -0500
  Re: single instance Roedy Green <see_website@mindprod.com.invalid> - 2013-01-03 07:12 -0800
    Re: single instance Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2013-01-03 09:56 -0800
      Re: single instance Martin Gregorie <martin@address-in-sig.invalid> - 2013-01-03 21:05 +0000
        Re: single instance Martin Gregorie <martin@address-in-sig.invalid> - 2013-01-03 22:08 +0000
        Re: single instance "Chris Uppal" <chris.uppal@metagnostic.REMOVE-THIS.org> - 2013-01-05 12:48 +0000
          Re: single instance Martin Gregorie <martin@address-in-sig.invalid> - 2013-01-05 17:43 +0000
            Re: single instance Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2013-01-05 09:49 -0800
            Re: single instance Twirlip of the Mists <twirlip@killfile.me.now.invalid> - 2013-01-05 13:02 -0500
              Re: single instance Martin Gregorie <martin@address-in-sig.invalid> - 2013-01-05 20:29 +0000
                Re: single instance Roedy Green <see_website@mindprod.com.invalid> - 2013-01-05 19:07 -0800
                Re: single instance Twirlip of the Mists <twirlip@killfile.me.now.invalid> - 2013-01-06 20:04 -0500
            Re: single instance Arne Vajhøj <arne@vajhoej.dk> - 2013-01-05 21:40 -0500
    Re: single instance Arne Vajhøj <arne@vajhoej.dk> - 2013-01-05 22:10 -0500
      Re: single instance Knute Johnson <nospam@knutejohnson.com> - 2013-01-05 19:49 -0800
        Re: single instance Arne Vajhøj <arne@vajhoej.dk> - 2013-01-05 23:09 -0500
          Re: single instance Arne Vajhøj <arne@vajhoej.dk> - 2013-01-06 11:00 -0500
            Re: single instance Lew <lewbloch@gmail.com> - 2013-01-06 09:41 -0800
              Re: single instance Arne Vajhøj <arne@vajhoej.dk> - 2013-01-06 20:41 -0500
        Re: single instance Roedy Green <see_website@mindprod.com.invalid> - 2013-01-15 22:51 -0800
          Re: single instance Roedy Green <see_website@mindprod.com.invalid> - 2013-01-15 23:12 -0800
            Re: single instance Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2013-01-15 23:49 -0800
          Re: single instance Roedy Green <see_website@mindprod.com.invalid> - 2013-01-15 23:16 -0800
            Re: single instance Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2013-01-15 23:52 -0800
            Re: single instance Knute Johnson <nospam@knutejohnson.com> - 2013-01-16 08:46 -0800
              Re: single instance Roedy Green <see_website@mindprod.com.invalid> - 2013-01-16 10:46 -0800
                Re: single instance markspace <markspace@nospam.nospam> - 2013-01-16 13:01 -0800
                Re: single instance Knute Johnson <nospam@knutejohnson.com> - 2013-01-16 17:10 -0800
          Re: single instance Roedy Green <see_website@mindprod.com.invalid> - 2013-01-15 23:50 -0800
            Re: single instance Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2013-01-16 00:13 -0800
              Re: single instance Roedy Green <see_website@mindprod.com.invalid> - 2013-01-16 02:48 -0800
                Re: single instance Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2013-01-16 07:28 -0800
                Re: single instance Roedy Green <see_website@mindprod.com.invalid> - 2013-01-16 10:46 -0800
                Re: single instance Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2013-01-16 16:53 -0800
                Re: single instance Roedy Green <see_website@mindprod.com.invalid> - 2013-01-16 23:44 -0800
                Re: single instance Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2013-01-17 07:03 -0800
                Re: single instance Roedy Green <see_website@mindprod.com.invalid> - 2013-01-17 14:25 -0800
                Re: single instance Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2013-01-17 16:31 -0800
                Re: single instance Roedy Green <see_website@mindprod.com.invalid> - 2013-01-17 22:11 -0800
                Re: single instance Roedy Green <see_website@mindprod.com.invalid> - 2013-01-17 22:36 -0800
              Re: single instance Arne Vajhøj <arne@vajhoej.dk> - 2013-01-16 13:34 -0500
          Re: single instance Knute Johnson <nospam@knutejohnson.com> - 2013-01-16 08:45 -0800
          Re: single instance Arne Vajhøj <arne@vajhoej.dk> - 2013-01-16 13:29 -0500
            Re: single instance Knute Johnson <nospam@knutejohnson.com> - 2013-01-16 17:14 -0800
              Re: single instance Arne Vajhøj <arne@vajhoej.dk> - 2013-01-16 20:20 -0500
              Re: single instance Roedy Green <see_website@mindprod.com.invalid> - 2013-01-16 23:52 -0800
              Re: single instance Roedy Green <see_website@mindprod.com.invalid> - 2013-01-17 01:44 -0800
        Re: single instance Roedy Green <see_website@mindprod.com.invalid> - 2013-01-18 01:47 -0800
          Re: single instance Knute Johnson <nospam@knutejohnson.com> - 2013-01-18 20:50 -0800
            Re: single instance Roedy Green <see_website@mindprod.com.invalid> - 2013-01-20 00:53 -0800
              Re: single instance Lew <lewbloch@gmail.com> - 2013-01-20 12:00 -0800
                Re: single instance Knute Johnson <nospam@knutejohnson.com> - 2013-01-20 13:33 -0800
                Re: single instance Arne Vajhøj <arne@vajhoej.dk> - 2013-02-24 18:12 -0500
              Re: single instance Arne Vajhøj <arne@vajhoej.dk> - 2013-01-20 21:33 -0500
      Re: single instance "Chris Uppal" <chris.uppal@metagnostic.REMOVE-THIS.org> - 2013-01-06 13:34 +0000
  Re: single instance Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2013-01-04 10:26 -0800
    Re: single instance Twirlip of the Mists <twirlip@killfile.me.now.invalid> - 2013-01-04 14:04 -0500
  Re: single instance stledger@lanl.gov - 2013-01-16 14:51 -0800
    Re: single instance stledger@lanl.gov - 2013-01-16 15:09 -0800

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