it's up to you to make sure that children do not outlive their parent. under many circumstances ruby will take of this before you but there are certain situations which no process cannot deal with... my slave lib addresses this in a full proof way, but a solid understanding of process management is required to use it.
It seems slave-1.2.1 does what I want: Start a background worker
process, leave it alone, and be sure it stops when the main process
ends. I have inserted the following in my config/environment.rb:
The method MyWorker#run never returns. Does this look OK? Is
Slave::object designed for usage such as this?
Uwe
···
On Sat, 2008-02-02 at 07:41 +0900, ara howard wrote:
On Feb 1, 2008, at 3:21 PM, Uwe Kubosch wrote:
> Can anybody explain to me why child processes continue to live after
> their parent process has ended?
it's up to you to make sure that children do not outlive their
parent. under many circumstances ruby will take of this before you
but there are certain situations which no process cannot deal with...
my slave lib addresses this in a full proof way, but a solid
understanding of process management is required to use it.
Can anybody explain to me why child processes continue to live after
their parent process has ended?
google 'zombie process'
The OP was not really describing zombies but instead orphaned processes.
I have no doubt that Ara understands the differences but for other folks:
A zombie process is a child process that has terminated but is being ignored by its parent. The process hangs around in the zombie state until the parent waits for it in order to 'reap' its termination status.
A process that gets orphaned when its parent dies will get inherited by the init process, which will take care of reaping the termination status of an adopted processes when/if it terminates. An orphaned process is not notified that it has been orphaned but in theory it could see that its parent process id has changed (Process.ppid) or that its parent is init (process id 1).
So while a parent process needs to pay attention to the status of its children, a child process doesn't really have to know anything about its parent.
Ara Howard wrote:
it's up to you to make sure that children do not outlive their parent.
Ara, are you talking more about making sure that you are reaping child processes? The idea that your child process will outlive you is quite common, for example when a daemon is started. It will often outlive whatever started it.
The typical way to explicitly orphan a process (so that it gets adopted by init) is a double fork:
fork { fork { do_work }; exit }
The intermediary process forks a child process to do the work and then exits. The original process waits for the intermediary and the 'grandchild' is orphaned and inherited by init. There are more considerations though to make a true 'daemon' process.
A good source of information for this type of programming is Advanced Programming in the Unix Environment, by Rich Stevens and Stephen Rago (2nd Edition).
Ara, are you talking more about making sure that you are reaping child processes? The idea that your child process will outlive you is quite common, for example when a daemon is started. It will often outlive whatever started it.
well - i wasn't really talking about reaping, but killing
the only way i've found to *really* prevent a child from outliving it's parent is what slave.rb does internally which connect a lifeline from child to parent - that lifeline is a pipe. the basic concept is (with syntax error i'm sure)
r, w = IO.pipe
fork do
w.close
Thread.new do
begin
r.read
rescue Exception
Kernel.exit
end
end
child_stuff()
exit
end
r.close
which is to say open a pipe, spawn a child, ensure the child exist if the pipe ever goes stale. this makes a child die even if the parent gets 'kill -9'ed
On Feb 1, 2008, at 4:45 PM, Gary Wright wrote:
--
we can deny everything, except that we have the possibility of being better. simply reflect on that.
h.h. the 14th dalai lama
I see. That makes sense and avoids any sort of ugly polling mechanism.
···
On Feb 1, 2008, at 11:22 PM, ara howard wrote:
well - i wasn't really talking about reaping, but killing
the only way i've found to *really* prevent a child from outliving it's parent is what slave.rb does internally which connect a lifeline from child to parent - that lifeline is a pipe. the basic concept is (with syntax error i'm sure)
