Brian Underwood <[email protected]> wrote:
> In the Rails 3 application that I support, we sometimes fork during a
> web request in order to do background processing behind the scenes
> without the user (and the browser connection) to wait for it to
> finish. I realize that a better method would be to have a queue of
> jobs to be processed (I even created a gem called job_boss which works
> well for our case), but it will take us a while to get there, so I'm
> trying to fix this for now.
>
> The problem that I'm finding is that, when I fork, the HTTP connection
> doesn't close. IE doesn't handle this as well and the browser is left
> sitting, waiting for the child process to finish rather than being
> redirected. This functionality worked fine in our application when we
> were using Rails 2.3.5 and Unicorn 1.1.3, but broke when we moved to
> Rails 3 and Unicorn 3.0.0 (we've since moved to Unicorn 3.4.0 and the
> problem remains, I had some hope that Unicorn 3.3.1 might have
> addressed it).
I'm not able to reproduce any difference between 1.x and 3.x in this
regard in forking behavior. I know that the client socket is never
closed on fork by default, so there's probably something else in your
app that changed...
> I've been able to solve this problem temporarily by closing two file
> descriptors manually (#3 and, depending on the version of Rails #6 or
> #7). Obviously this is not ideal. I found the UNICORN_FD environment
> variable when looking through the Unicorn source, but that only seems
> to indicate #3. Where might #6/#7 be coming from?
Whatever is in UNICORN_FD is the listener socket (probably 3), so 6/7 is
probably the client socket, but you should normally close everything in
the forked child for background processing.
The IO.closefrom method in the io-extra[1] gem will get everything
including descriptors opened without a corresponding Ruby object.
If you know everything uses Ruby IO, then walking ObjectSpace works,
too:
# close everything except stdin, stdout and stderr
ObjectSpace.each_object(IO) { |s|
begin
s.close if s.fileno > 2
rescue IOError, Errno::EBADF
# EBADF can come from duplicate IOs due to FD inheritance
end
}
> Is there some way
> that I can determine these without hard-coding the FD #?
lsof or scanning /proc/$$/fd (Linux), but if you have any open socket
connections (memcached/activerecord/net-http-persistent/etc...), you
should close all of those and restart them if necessary in the child.
[1] http://rubyforge.org/projects/shards
--
Eric Wong
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