[Installit-dev] "package manager " becomes "InstallIt"

[Benedikt Meurer]

Jannis Pohlmann wrote:
>>>>>Use kill($PID, 0) rather than /proc/$PID and you're ok. Trust me, it's 
>>>>>really not worth the trouble with fcntl()/lockf() locking. And we're not 
>>>>>developing a critical database, so if a user manages to start two 
>>>>>instances of InstallIt, then he'll run into trouble and may remember to 
>>>>>read the documentation when he uses a software next time. ;-)
>>>>
>>>>i tried this (it's in SVN, see Core/LockFile and i2t for the usage). It
>>>>doesn't really work at all. What did you expect it to do?
>>>
>>>
>>>Just checked it. Seems to work fine, except that you still use /proc
>>>instead of kill().
> 
> yes, I commented out the kill() thing for one reason: It didn't do
> anything useful. I asked myself what you could have meant by suggesting
> kill() and came to the conclusion that your intend was to kill the
> running instance before starting the new one, right? Well, I'd prefer
> aborting the program if another instance already is running.
> 
> I couldn't find a platform-independent way for determining if a process
> with a certain PID is running or not, this is why I used /proc. I'm
> still not sure about this, perhaps fcntl/lockf is better anyway.

The platform independent way is to use kill(pid, 0). 0 is a special
signal, that is not delivered to the target process, but is handled by
the kernel completely. The kernel will check if the process with the
given pid is still alive and if so, respond with 0, else it responds
with an error, telling you that the process is gone (or you don't have
permission to talk to the process).

> - Jannis

Benedikt