[Twisted-Python] Incorrect "Another twistd server is running..."

[Simone Deponti]

On 07/21/2009 04:06 PM, Jean-Paul Calderone wrote:
> This is probably due to<http://twistedmatrix.com/trac/ticket/3851>.  It's
> not clear what the best solution is yet.

Hi all,

In the bug report I see:

 > after an unclean shutdown by a previous twistd, a new process is
 > started and is allocated the same pid as is in the pidfile which was
 > left behind. This process now causes twistd to think another twistd
 > process is still running in the directory.

If I understand well, the (rather unlucky, but not all that improbable) 
case we are talking about here is twisted getting reassigned the same 
PID that it was running with before?

Example:
1. Twisted is running with PID 401 and suffers an unclean shutdown.
2. Twisted is restarted and is reassigned the same PID (likely if it's a 
daemon launched during startup and a reboot has happened)
3. Twisted invokes checkPID (which reads from the stale pidfile) and 
sees that, after all, there is a process 401 running
4. Twisted claims another process is running

Why this can't be solved by comparing the pid in the file with 
os.getpid() (before throwing the error)?