Is Sinatra multi threaded? - ruby

Question

Is Sinatra multi-threaded? I read else where that "sinatra is multi-threaded by default", what does that imply?
Consider this example
get "/multithread" do
t1 = Thread.new{
puts "sleeping for 10 sec"
sleep 10
# Actually make a call to Third party API using HTTP NET or whatever.
}
t1.join
"multi thread"
end
get "/dummy" do
"dummy"
end
If I access "/multithread" and "/dummy" subsequently in another tab or browser then nothing can be served(in this case for 10 seconds) till "/multithread" request is completed. In case activity freezes application becomes unresponsive.
How can we work around this without spawning another instance of the application?

Answer 1

tl;dr Sinatra works well with Threads, but you will probably have to use a different web server.
Sinatra itself does not impose any concurrency model, it does not even handle concurrency. This is done by the Rack handler (web server), like Thin, WEBrick or Passenger. Sinatra itself is thread-safe, meaning that if your Rack handler uses multiple threads to server requests, it works just fine. However, since Ruby 1.8 only supports green threads and Ruby 1.9 has a global VM lock, threads are not that widely used for concurrency, since on both versions, Threads will not run truly in parallel. The will, however, on JRuby or the upcoming Rubinius 2.0 (both alternative Ruby implementations).
Most existing Rack handlers that use threads will use a thread pool in order to reuse threads instead of actually creating a thread for each incoming request, since thread creation is not for free, esp. on 1.9 where threads map 1:1 to native threads. Green threads have far less overhead, which is why fibers, which are basically cooperatively scheduled green threads, as used by the above mentioned sinatra-synchrony, became so popular recently. You should be aware that any network communication will have to go through EventMachine, so you cannot use the mysql gem, for instance, to talk to your database.
Fibers scale well for network intense processing, but fail miserably for heavy computations. You are less likely to run into race conditions, a common pitfall with concurrency, if you use fibers, as they only do a context switch at clearly defined points (with synchony, whenever you wait for IO). There is a third common concurrency model: Processes. You can use preforking server or fire up multiple processes yourself. While this seems a bad idea at first glance, it has some advantages: On the normal Ruby implementation, this is the only way to use all your CPUs simultaniously. And you avoid shared state, so no race conditions by definition. Also, multiprocess apps scale easily over multiple machines. Keep in mind that you can combine multiple process with other concurrency models (evented, cooperative, preemptive).
The choice is mainly made by the server and middleware you use:
Multi-Process, non-preforking: Mongrel, Thin, WEBrick, Zbatery
Multi-Process, preforking: Unicorn, Rainbows, Passenger
Evented (suited for sinatra-synchrony): Thin, Rainbows, Zbatery
Threaded: Net::HTTP::Server, Threaded Mongrel, Puma, Rainbows, Zbatery, Thin[1], Phusion Passenger Enterprise >= 4
[1] since Sinatra 1.3.0, Thin will be started in threaded mode, if it is started by Sinatra (i.e. with ruby app.rb, but not with the thin command, nor with rackup).

Answer 2

While googling around, found this gem:
sinatra-synchrony
which might help you, because it touches you question.
There is also a benchmark, they did nearly the same thing like you want (external calls).
Conclusion: EventMachine is the answer here!

Answer 3

Thought I might elaborate for people who come across this. Sinatra includes this little chunk of code:
server.threaded = settings.threaded if server.respond_to? :threaded=
Sinatra will detect what gem you have installed for a webserver (aka, thin, puma, whatever.) and if it responds to "threaded" will set it to be threaded if requested. Neat.

Answer 4

After making some changes to code I was able to run padrino/sinatra application on mizuno
. Initially I tried to run Padrino application on jRuby but it was simply too unstable and I did not investigate as to why. I was facing JVM crashes when running on jRuby. I also went through this article, which makes me think why even choose Ruby if deployment can be anything but easy.
Is there any discussion on deployment of applications in ruby? Or can I spawn a new thread :)

Answer 5

I've been getting in to JRuby myself lately and I am extremely surprised how simple it is to switch from MRI to JRuby. It pretty much involves swapping out a few gems (in most cases).
You should take a look at the combination JRuby and Trinidad (App Server). Torquebox also seems to be an interesting all-in-one solution, it comes with a lot more than just an app server.
If you want to have an app server that supports threading, and you're familiar with Mongrel, Thin, Unicorn, etc, then Trinidad is probably the easiest to migrate to since it's practically identical from the users perspective. Loving it so far!