implemented pooling for Docker containers

lib/docker_container_pool.rb

@@ -0,0 +1,52 @@
+require 'concurrent/future'
+require 'concurrent/timer_task'
+require 'concurrent/utilities'
+
+class DockerContainerPool
+  @containers = ThreadSafe::Hash[ExecutionEnvironment.all.map { |execution_environment| [execution_environment.id, ThreadSafe::Array.new] }]
+
+  def self.clean_up
+    @refill_task.try(:shutdown)
+    @containers.each do |key, value|
+      while !value.empty? do
+        DockerClient.destroy_container(value.shift)
+      end
+    end
+  end
+
+  def self.config
+    @config ||= CodeOcean::Config.new(:docker).read(erb: true)[:pool]
+  end
+
+  def self.create_container(execution_environment)
+    DockerClient.create_container(execution_environment)
+  end
+
+  def self.get_container(execution_environment)
+    if config[:active]
+      @containers[execution_environment.id].try(:shift) || create_container(execution_environment)
+    else
+      create_container(execution_environment)
+    end
+  end
+
+  def self.quantities
+    @containers.map { |key, value| [key, value.length] }.to_h
+  end
+
+  def self.refill
+    ExecutionEnvironment.all.each do |execution_environment|
+      refill_count = execution_environment.pool_size - @containers[execution_environment.id].length
+      if refill_count > 0
+        Concurrent::Future.execute do
+          @containers[execution_environment.id] += refill_count.times.map { create_container(execution_environment) }
+        end
+      end
+    end
+  end
+
+  def self.start_refill_task
+    @refill_task = Concurrent::TimerTask.new(execution_interval: config[:interval], run_now: true) { refill }
+    @refill_task.execute
+  end
+end