You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: session_tracker.rb
    path of file: ./repos/bugsnag-ruby/lib/bugsnag
    
    the code of the file until where you have to start completion: require 'thread'
require 'time'
require 'securerandom'

module Bugsnag
  class SessionTracker
    THREAD_SESSION = "bugsnag_session"
    SESSION_PAYLOAD_VERSION = "1.0"
    MUTEX = Mutex.new

    attr_reader :session_counts

    ##
    # Sets the session information for this thread.
    def self.set_current_session(session
    
    def start_delivery_thread
      MUTEX.synchronize do
        @started = nil unless defined?(@started)
        return if @started == Process.pid
        @started = Process.pid
        at_exit do
          if !@delivery_thread.nil?
            @delivery_thread.execute
            @delivery_thread.shutdown
          else
            if @session_counts.size > 0
              send_sessions
            end
          end
        end