Whew! After a long day of debugging, I think I've gotten closer to isolating
this.
I've upgraded us to your pre-release gem but I can still get it working (both
before & after a lot of the below fixes)
>> After a USR2 signal our process tree winds up looking like this, with
>> several master-esque processes listed as children (but without the
>> "worker[N]" label):
>>
>> app 14402 4.4 0.8 199612 70264 ? S 14:07 0:04
>> unicorn_rails master -c config/unicorn.rb -E production -D
>> app 14433 0.0 0.8 204540 68504 ? Sl 14:07 0:00 \_
>> unicorn_rails worker[0] -c config/unicorn.rb -E production -D
>> app 14435 0.0 0.8 204540 68508 ? Sl 14:07 0:00 \_
>> unicorn_rails worker[1] -c config/unicorn.rb -E production -D
>> app 14438 0.0 0.8 199748 65840 ? S 14:07 0:00 \_
>> /usr/bin/ruby1.8 /usr/bin/unicorn_rails -c config/unicorn.rb -E production -D
>> app 14440 0.0 0.8 204540 68508 ? Sl 14:07 0:00 \_
>> unicorn_rails worker[3] -c config/unicorn.rb -E production -D
>> app 14442 0.0 0.8 204540 68508 ? Sl 14:07 0:00 \_
>> unicorn_rails worker[4] -c config/unicorn.rb -E production -D
>> app 14445 0.0 0.8 199760 65840 ? S 14:07 0:00 \_
>> /usr/bin/ruby1.8 /usr/bin/unicorn_rails -c config/unicorn.rb -E production -D
>> app 14447 0.0 0.8 204540 68508 ? Sl 14:07 0:00 \_
>> unicorn_rails worker[6] -c config/unicorn.rb -E production -D
>> app 14449 0.0 0.8 204780 69272 ? Sl 14:07 0:00 \_
>> unicorn_rails worker[7] -c config/unicorn.rb -E production -D
>>
>> Sending another USR2 signal will bring a new master into the mix as a
>> child, spins up a single child worker of its own (which also resembles
>> the "/usr/bin/ruby1.8" master-esque processes), and then fails to
>> continue.
>
> Anything in your before_fork/after_fork hooks? Since it looks like
> you're on a Linux system, can you strace the master while you send
> it a USR2 and see if anything strange happens?
The only real contents of our before_hook is a send-QUIT-on-first-worker, which
I swapped out for the default SIGTTOU behavior. No change.
> I assume you're using regular "unicorn" to run your Sinatra apps and not
> "unicorn_rails". I made some largish cleanups to both for the 0.97.0
> release and and perhaps some bugs slipped into the "_rails" variant.
>
> Not sure if it's a problem, but with Bundler I assume Rack itself is a
> bundled dependency, but you're starting unicorn_rails out of
> /usr/bin/unicorn_rails which indicates Unicorn is not bundled (and won't
> use the bundled Rack). Can you ensure your unbundled Rack is the same
> version as the bundled one to be on the safe side?
>
My system & bundled rack versions match.
Swapped to vanilla "unicorn" instead of "unicorn_rails" -- also no dice
I switched to using "bundle exec unicorn", which uses
RAILS_ROOT/vendor/bundler_gems/bin/unicorn instead of /usr/bin/unicorn. Was
convinced this would be it, but no dice.
Attaching some relevant stack traces... the new "orphan" master & its 1st child
are pretty boring while just hanging out:
Process 20738 attached - interrupt to quit
futex(0x2aaaaafb23c0, FUTEX_WAIT, 2, NULL
Sending a USR2 to the new, orphaned master...
Process 20738 attached - interrupt to quit
select(10, [9], [], [], {23, 661000}) = ? ERESTARTNOHAND (To be restarted)
--- SIGUSR2 (User defined signal 2) @ 0 (0) ---
rt_sigreturn(0xc) = -1 EINTR (Interrupted system call)
rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
clock_gettime(CLOCK_MONOTONIC, {2782804, 359708496}) = 0
select(0, [], [], [], {0, 0}) = 0 (Timeout)
rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0
fcntl(5, F_GETFL) = 0x801 (flags O_WRONLY|O_NONBLOCK)
write(5, "."..., 1) = 1
clock_gettime(CLOCK_MONOTONIC, {2782804, 360046496}) = 0
select(10, [9], [], [], {20, 464341}
I've also produced straces of the *original* master during USR2 restarts, both
a success trace and a failure trace.
Here's a tarball with both complete traces as well as filtered/grepp'd ones:
http://jamiedubs.com/files/unicorn-strace.tgz
I've also found that kill -9'ing the 1st worker of the new orphaned master
allows it to continue operation as normal (spinning up workers and taking
control from the original master) -- suggesting something is up with just that
first worker (!). I'm going to keep noodling with before_/after_fork strategies.
-jamie
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