static or stuff like that

static or stuff like that

[Wrazlov]

Hi there,
I want to control whether a process is already running or not, and i don't 
know how without using some kind of lock-files, wasn't there something like
static int x=0;
or stuff like that to get how many processes are running?

Re: static or stuff like that

[Glynn Clements]

Wrazlov wrote:

> I want to control whether a process is already running or not, and i don't 
> know how without using some kind of lock-files

You can scan the files under /proc/<pid> to obtain details about which
processes are running. E.g. /proc/<pid>/exe is a symlink to the
program which process <pid> is executing.

-- 
Glynn Clements <glynn.clements@virgin.net>

Re: static or stuff like that

[wwp]

Hi Glynn,


On Sun, 28 Apr 2002 22:52:39 +0100 Glynn Clements <glynn.clements@virgin.net> wrote:

> 
> Wrazlov wrote:
> 
> > I want to control whether a process is already running or not, and i don't 
> > know how without using some kind of lock-files
> 
> You can scan the files under /proc/<pid> to obtain details about which
> processes are running. E.g. /proc/<pid>/exe is a symlink to the
> program which process <pid> is executing.

Is /proc always available? (if not, how to do what Wrazlov asked?)


Regards

-- 
wwp

Re: static or stuff like that

[Glynn Clements]

wwp wrote:

> > > I want to control whether a process is already running or not, and i don't 
> > > know how without using some kind of lock-files
> > 
> > You can scan the files under /proc/<pid> to obtain details about which
> > processes are running. E.g. /proc/<pid>/exe is a symlink to the
> > program which process <pid> is executing.
> 
> Is /proc always available?

It's possible that /proc isn't mounted but, if it isn't, many OS
features won't work (e.g. modprobe). Unless you're targeting a very
minimal system (e.g. embedded systems), or writing code which will run
early in the boot sequence, it's safe to assume that /proc will be
available.

> (if not, how to do what Wrazlov asked?)

Without /proc, the only way in which you could obtain information on
other processes is by examining the kernel data structures via
/dev/kmem.

BTW, /dev/kmem is the traditional mechanism for implementing "ps", but
it has a number of drawbacks (e.g. requiring root privilege, having to
modify "ps" if the format of the relevant kernel data structures
changes).

-- 
Glynn Clements <glynn.clements@virgin.net>

Re: static or stuff like that

[wwp]

Hi Glynn,

On Mon, 29 Apr 2002 10:48:41 +0100 Glynn Clements
<glynn.clements@virgin.net> wrote:

> > > > I want to control whether a process is already running or not,
> > > > and i don't know how without using some kind of lock-files
> > > 
> > > You can scan the files under /proc/<pid> to obtain details about
> > > which processes are running. E.g. /proc/<pid>/exe is a symlink to
> > > the program which process <pid> is executing.
> > 
> > Is /proc always available?
> 
> It's possible that /proc isn't mounted but, if it isn't, many OS
> features won't work (e.g. modprobe). Unless you're targeting a very
> minimal system (e.g. embedded systems), or writing code which will run
> early in the boot sequence, it's safe to assume that /proc will be
> available.
[snip]

Thanx for your answers.
I've also seen software using unix domain socket to prohibit duplicate
launch of a program on a POSIX system.
What do you think of this method, Glynn?


Regards,

-- 
wwp

Re: static or stuff like that

[Glynn Clements]

wwp wrote:

> > > > > I want to control whether a process is already running or not,
> > > > > and i don't know how without using some kind of lock-files
> > > > 
> > > > You can scan the files under /proc/<pid> to obtain details about
> > > > which processes are running. E.g. /proc/<pid>/exe is a symlink to
> > > > the program which process <pid> is executing.
> > > 
> > > Is /proc always available?
> > 
> > It's possible that /proc isn't mounted but, if it isn't, many OS
> > features won't work (e.g. modprobe). Unless you're targeting a very
> > minimal system (e.g. embedded systems), or writing code which will run
> > early in the boot sequence, it's safe to assume that /proc will be
> > available.
> [snip]
> 
> Thanx for your answers.
> I've also seen software using unix domain socket to prohibit duplicate
> launch of a program on a POSIX system.
> What do you think of this method, Glynn?

I don't see that this is any different to using a lock file.

-- 
Glynn Clements <glynn.clements@virgin.net>