Thread safe multitenancy in Rails 5.0

Question

I'm working on a legacy code base in Rails 5.0 where there isn't really the resources for upgrading to a newer version. That said, I'm trying to understand whether or not this solution would be thread safe and if not, what can be done to improve it. I have an Organization model and many other models tied to this one but for simplicity, I'll stick with the User model.

class Organization < ApplicationRecord
  has_many :users, dependent: :destroy


  def self.current_id=(id)
    Thread.current[:organization_id] = id
  end

  def self.current_id
    Thread.current[:organization_id]
  end

  validates_uniqueness_of :name, presence: true
end

class User < ApplicationRecord

  devise :database_authenticatable,
         :rememberable, :trackable,
         :registerable

  belongs_to :organization

  default_scope { where(organization_id: Organization.current_id)}
end

This is my application controller

class ApplicationController < ActionController::Base
  protect_from_forgery with: :exception

  # get the organization from the domain before
  prepend_around_filter :scope_current_organization


  private

  def require_active_user!
    raise "Called ApplicationController#require_active_user! without user" unless user_signed_in?
    if !current_user.active?
      redirect_to inactive_account_path
    end
  end

  def current_organization
    Organization.find_by!(subdomain: request.subdomain)
  end
  helper_method :current_tenant

  def scope_current_organization
    Organization.current_id = current_organization.id
    yield
  ensure
    Organization.current_id = nil
  end
end

From my local development testing this solution seems to work but I'm wondering what aspects of thread safety I may have missed. Thanks in advance for your help!

From my local development testing this solution seems to work but I'm wondering what aspects of thread safety I may have missed. Thanks in advance for your help!