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*[Part 0: Before reading Rails 5 source code](#part-0-before-reading-rails-5-source-code)

1) I suggest you learn Rack[http://rack.github.io/](http://rack.github.io/) first.

1) I suggest youtolearn Rack[http://rack.github.io/](http://rack.github.io/) first.

Inrack, an object with`call` method is arack app.

InRack, an object with`call` method is aRack app.

So what is the object with`call` method in Rails? I will answer this question in Part 1.

* How does Rails combine ActionController, ActionView and Routes together?

* How doespuma, rack, Rails work together?

* How doesPuma, Rack, Rails work together?

* What's Puma's multiple threads?

Rails::Server.new(server_options).tapdo |server|

Arack server need to start with an`App` object. The`App` object should have a`call` method.

ARack server need to start with an`App` object. The`App` object should have a`call` method.

`config.ru` is the conventional entry file forrack app. So let's look at it.

`config.ru` is the conventional entry file forRack app. So let's look at it.

`Rails.application` is an important object in Rails.

And you'll only have one`Rails.application` in onepuma process.

And you'll only have one`Rails.application` in onePuma process.

Multiple threads in apuma process shares the`Rails.application`.

Multiple threads in aPuma process shares the`Rails.application`.

The first time we see the`config` is in`./config/application.rb`.

When a request is made from client,puma will process the request in`Puma::Server#process_client`.

When a request is made from client,Puma will process the request in`Puma::Server#process_client`.

If you want to know howpuma enter the method`Puma::Server#process_client`, please read part 4 or just search 'process_client' in this document.

If you want to know howPuma enter the method`Puma::Server#process_client`, please read part 4 or just search 'process_client' in this document.

defhandle_request(req,lines)

@app||@app_build_lock.synchronize {# '@app_build_lock = Mutex.new', so multiple threads share one '@app'.

defbuild(app)

klass.new(app,*args,&block)

As we see in the Rack middleware stack, the lastone is

As we see in the Rack middleware stack, the last@app is

After allrack apps called, user will get the response.

After allRack apps called, user will get the response.

Rails::Server.new(server_options).tapdo |server|

definitialize(conf,launcher_args={})

@thread_pool=ThreadPool.new(@min_threads,

@max_threads,

IOBuffer)do |client,buffer|

if process_now

process_client(client, buffer)

if background# background: true (for this example)

breakif handle_check

if io= sock.accept_nonblock

client=Client.new(io,@binder.env(sock))

definitialize(min,max,*extra,&block)

@mutex=Mutex.new

@todo= []# @todo is requests (inpuma, they are Puma::Client instances) which need to be processed.

@todo= []# @todo is requests (inPuma, they are Puma::Client instances) which need to be processed.

@min=Integer(min)# @min threads count

@max=Integer(max)# @max threads count

work= todo.shiftif continue

@todo<< work

if@waiting<@todo.sizeand@spawned<@max

Request is created from`ios` object.

A thread inpuma threadPool will process the request.

A thread inPuma threadPool will process the request.

The thread will invokerack apps'`call` to get the response for the request.

The thread will invokeRack apps'`call` to get the response for the request.

When you stoppuma by running`$ kill -s SIGTERM puma_process_id`, you will enter`setup_signals`in`Puma::Launcher#run`.

When you stopPuma by running`$ kill -s SIGTERM puma_process_id`, you will enter`setup_signals`in`Puma::Launcher#run`.

# The created @thread is the @thread in`stop` method below.

@mutex=Mutex.new

@todo= []# @todo is requests (inpuma, it's Puma::Client instance) which need to be processed.

@todo= []# @todo is requests (inPuma, it's Puma::Client instance) which need to be processed.

@min=Integer(min)# @min threads count

@block= block# block will be called in method `spawn_thread` to process a request.

@workers= []