Class: Async::Container::Controller

Inherits:
Object
  • Object
show all
Defined in:
lib/async/container/controller.rb

Overview

Manages the life-cycle of one or more containers in order to support a persistent system. e.g. a web server, job server or some other long running system.

Constant Summary collapse

SIGHUP = 
Signal.list["HUP"]
SIGINT = 
Signal.list["INT"]
SIGTERM = 
Signal.list["TERM"]
SIGUSR1 = 
Signal.list["USR1"]
SIGUSR2 = 
Signal.list["USR2"]

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(notify: Notify.open!, container_class: Container) ⇒ Controller

Initialize the controller.



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# File 'lib/async/container/controller.rb', line 25

def initialize(notify: Notify.open!, container_class: Container)
	@container = nil
	@container_class = container_class
	
	if @notify = notify
		@notify.status!("Initializing...")
	end
	
	@signals = {}
	
	trap(SIGHUP) do
		self.restart
	end
end

Instance Attribute Details

#container ⇒ Object (readonly)

The current container being managed by the controller.



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# File 'lib/async/container/controller.rb', line 64

def container
  @container
end

Instance Method Details

#create_container ⇒ Object

Create a container for the controller. Can be overridden by a sub-class.



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# File 'lib/async/container/controller.rb', line 69

def create_container
	@container_class.new
end

#reload ⇒ Object

Reload the existing container. Children instances will be reloaded using ‘SIGHUP`.



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# File 'lib/async/container/controller.rb', line 153

def reload
	@notify&.reloading!
	
	Console.logger.info(self) {"Reloading container: #{@container}..."}
	
	begin
		self.setup(@container)
	rescue
		raise SetupError, container
	end
	
	# Wait for all child processes to enter the ready state.
	Console.logger.debug(self, "Waiting for startup...")
	@container.wait_until_ready
	Console.logger.debug(self, "Finished startup.")
	
	if @container.failed?
		@notify.error!("Container failed to reload!")
		
		raise SetupError, @container
	else
		@notify&.ready!
	end
end

#restart ⇒ Object

Restart the container. A new container is created, and if successful, any old container is terminated gracefully. This is equivalent to a blue-green deployment.



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# File 'lib/async/container/controller.rb', line 106

def restart
	if @container
		@notify&.restarting!
		
		Console.logger.debug(self) {"Restarting container..."}
	else
		Console.logger.debug(self) {"Starting container..."}
	end
	
	container = self.create_container
	
	begin
		self.setup(container)
	rescue => error
		@notify&.error!(error.to_s)
		
		raise SetupError, container
	end
	
	# Wait for all child processes to enter the ready state.
	Console.logger.debug(self, "Waiting for startup...")
	container.wait_until_ready
	Console.logger.debug(self, "Finished startup.")
	
	if container.failed?
		@notify&.error!("Container failed to start!")
		
		container.stop
		
		raise SetupError, container
	end
	
	# Make this swap as atomic as possible:
	old_container = @container
	@container = container
	
	Console.logger.debug(self, "Stopping old container...")
	old_container&.stop
	@notify&.ready!
rescue
	# If we are leaving this function with an exception, try to kill the container:
	container&.stop(false)
	
	raise
end

#run ⇒ Object

Enter the controller run loop, trapping ‘SIGINT` and `SIGTERM`.



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# File 'lib/async/container/controller.rb', line 179

def run
	# I thought this was the default... but it doesn't always raise an exception unless you do this explicitly.
	# We use `Thread.current.raise(...)` so that exceptions are filtered through `Thread.handle_interrupt` correctly.
	interrupt_action = Signal.trap(:INT) do
		::Thread.current.raise(Interrupt)
	end
	
	terminate_action = Signal.trap(:TERM) do
		::Thread.current.raise(Terminate)
	end
	
	hangup_action = Signal.trap(:HUP) do
		::Thread.current.raise(Hangup)
	end
	
	self.start
	
	while @container&.running?
		begin
			@container.wait
		rescue SignalException => exception
			if handler = @signals[exception.signo]
				begin
					handler.call
				rescue SetupError => error
					Console.logger.error(self) {error}
				end
			else
				raise
			end
		end
	end
rescue Interrupt
	self.stop(true)
rescue Terminate
	self.stop(false)
ensure
	self.stop(true)
	
	# Restore the interrupt handler:
	Signal.trap(:INT, interrupt_action)
	Signal.trap(:TERM, terminate_action)
	Signal.trap(:HUP, hangup_action)
end

#running? ⇒ Boolean

Whether the controller has a running container.

Returns:

  • (Boolean) 


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# File 'lib/async/container/controller.rb', line 75

def running?
	!!@container
end

#setup(container) ⇒ Object

Spawn container instances into the given container. Should be overridden by a sub-class.



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# File 'lib/async/container/controller.rb', line 87

def setup(container)
	# Don't do this, otherwise calling super is risky for sub-classes:
	# raise NotImplementedError, "Container setup is must be implemented in derived class!"
end

#start ⇒ Object

Start the container unless it’s already running.



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# File 'lib/async/container/controller.rb', line 93

def start
	self.restart unless @container
end

#state_string ⇒ Object

The state of the controller.



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# File 'lib/async/container/controller.rb', line 42

def state_string
	if running?
		"running"
	else
		"stopped"
	end
end

#stop(graceful = true) ⇒ Object

Stop the container if it’s running.



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# File 'lib/async/container/controller.rb', line 99

def stop(graceful = true)
	@container&.stop(graceful)
	@container = nil
end

#to_s ⇒ Object

A human readable representation of the controller.



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# File 'lib/async/container/controller.rb', line 52

def to_s
	"#{self.class} #{state_string}"
end

#trap(signal, &block) ⇒ Object

Trap the specified signal.



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# File 'lib/async/container/controller.rb', line 59

def trap(signal, &block)
	@signals[signal] = block
end

#wait ⇒ Object

Wait for the underlying container to start.



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# File 'lib/async/container/controller.rb', line 80

def wait
	@container&.wait
end