Re: unicorn stuck in sched_yield after ERESTARTNOHAND

[Bharanee Rathna <deepfryed@gmail.com>]

thanks for the quick response eric,

On Wed, Jun 1, 2011 at 9:48 AM, Eric Wong <normalperson@yhbt.net> wrote:
> Bharanee Rathna <deepfryed@gmail.com> wrote:
>> I'm encountering a weird error where the unicorn workers are stuck in
>> a loop after hitting a 500 on the backend sinatra app.
>
> Also, what extensions are you using in your app?

heaps of em. yajl, swift, rmagick, fastcaptcha, flock, nokogiri &
curb.  except swift and curb none of the others would be touching the
network.

>> strace at the point where it starts to go into a loop of death
>
>> select(7, [4 5], NULL, [3 6], {30, 0})  = 1 (in [5], left {27, 274382})
>> fchmod(8, 01)                           = 0
>> fcntl(5, F_GETFL)                       = 0x802 (flags O_RDWR|O_NONBLOCK)
>> accept4(5, {sa_family=AF_INET, sin_port=htons(56728),
>> sin_addr=inet_addr("10.1.1.4")}, [16], SOCK_CLOEXEC) = 12
>> recvfrom(12, 0x1c99fb0, 16384, 64, 0, 0) = -1 EAGAIN (Resource
>> temporarily unavailable)
>
> (I'm somewhat more awake, now, haven't been sleeping much)
>
> Two things look off in the line above:
>
> 1) recvfrom() isn't using the MSG_DONTWAIT flag.  I know you're using
>   Linux, so kgio should be using MSG_DONTWAIT to do non-blocking
>   recv...  Which versions of unicorn/kgio are you using?

using kgio 2.3.2, i'll upgrade it and give it another try

>
> 2) TCP_DEFER_ACCEPT should prevent recvfrom() from hitting EAGAIN
>   in the common case under Linux.
>
>> select(13, [12], NULL, NULL, NULL)      = ? ERESTARTNOHAND (To be restarted)
>> --- SIGINT (Interrupt) @ 0 (0) ---
>> rt_sigreturn(0x2)                       = -1 EINTR (Interrupted system call)
>
> What triggered SIGINT?

not sure

>
> Actually, after many lines of sched_yield() in your gist, I can see it
> does actually exit the process.  Did you kill it with SIGINT?  If so, I
> see nothing wrong...

yes i killed it after the worker looked stuck and wasn't responding for 30s
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