Why workers die when sending KILL to master?

Why workers die when sending KILL to master?

[Iñaki Baz Castillo]

Hi, in my customized "unicorn" executable I create N forks in master process 
to behave as posix_mq readers.

I added a "at_exit" block just in master process so they are killed when the 
master receives a signal to terminate.

The only issue I'm experimenting is the fact that they are not killed if the 
master process receives a KILL signal. However Unicorn workers are terminated 
after master is killed with KILL signal. Could I know how such cool feature is 
implemented?

AFAIK when a process receives a KILL signal it just dies and cannot capture 
such signal so this should be a feature implemented in workers (in some way 
they can detect if master has died, am I right?). If so, could I be pointed to 
the exact code in which the feature is implemented? I would like to replicate 
it in my extra-processes.

Thanks a lot.

-- 
Iñaki Baz Castillo <ibc@aliax.net>
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Re: Why workers die when sending KILL to master?

[Eric Wong]

Iñaki Baz Castillo <ibc@aliax.net> wrote:
> Hi, in my customized "unicorn" executable I create N forks in master process 
> to behave as posix_mq readers.
> 
> I added a "at_exit" block just in master process so they are killed when the 
> master receives a signal to terminate.
> 
> The only issue I'm experimenting is the fact that they are not killed if the 
> master process receives a KILL signal. However Unicorn workers are terminated 
> after master is killed with KILL signal. Could I know how such cool feature is 
> implemented?
> 
> AFAIK when a process receives a KILL signal it just dies and cannot capture 
> such signal so this should be a feature implemented in workers (in some way 
> they can detect if master has died, am I right?). If so, could I be pointed to 
> the exact code in which the feature is implemented? I would like to replicate 
> it in my extra-processes.
> 

Hi Iñaki,

The worker_loop just compares Process.ppid with the original ppid it
was started with.  They wakeup from IO.select() every timeout/2 seconds
to check for original_ppid != ppid if the server is idle.

-- 
Eric Wong
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Re: Why workers die when sending KILL to master?

[Iñaki Baz Castillo]

El Sábado, 9 de Enero de 2010, Eric Wong escribió:
> The worker_loop just compares Process.ppid with the original ppid it
> was started with.  They wakeup from IO.select() every timeout/2 seconds
> to check for original_ppid != ppid if the server is idle.

Thanks, I was expecting exactly that as the ppid changes when the master 
process dies :) 


-- 
Iñaki Baz Castillo <ibc@aliax.net>
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Re: Why workers die when sending KILL to master?

[Iñaki Baz Castillo]

El Sábado, 9 de Enero de 2010, Iñaki Baz Castillo escribió:
> El Sábado, 9 de Enero de 2010, Eric Wong escribió:
> > The worker_loop just compares Process.ppid with the original ppid it
> > was started with.  They wakeup from IO.select() every timeout/2 seconds
> > to check for original_ppid != ppid if the server is idle.
> 
> Thanks, I was expecting exactly that as the ppid changes when the master
> process dies :)

I've implememented the same concept for my extra-processes in a similar way:

        ppid = Process.ppid
        Thread.new do
          loop do
            sleep 4
            if Process.ppid != ppid
              log.fatal "master process did, exiting"
              exit!
            end
          end
        end


-- 
Iñaki Baz Castillo <ibc@aliax.net>
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