class ConnectionPool

def self.after_fork
  INSTANCES.values.each do |pool|
    # We're on after fork, so we know all other threads are dead.
    # All we need to do is to ensure the main thread doesn't have a
    # checked out connection
    pool.checkin(force: true)
    pool.reload do |connection|
      # Unfortunately we don't know what method to call to close the connection,
      # so we try the most common one.
      connection.close if connection.respond_to?(:close)
    end
  end
  nil
end

def self.after_fork
  # noop
end

def self.wrap(options, &block)
  Wrapper.new(options, &block)
end

def available
  @available.length
end

def checkin: (force: false) -> untyped

def checkin(force: false)
  if ::Thread.current[@key]
    if ::Thread.current[@key_count] == 1 || force
      @available.push(::Thread.current[@key])
      ::Thread.current[@key] = nil
      ::Thread.current[@key_count] = nil
    else
      ::Thread.current[@key_count] -= 1
    end
  elsif !force
    raise ConnectionPool::Error, "no connections are checked out"
  end
  nil
end

def checkout(options = {})
  if ::Thread.current[@key]
    ::Thread.current[@key_count] += 1
    ::Thread.current[@key]
  else
    ::Thread.current[@key_count] = 1
    ::Thread.current[@key] = @available.pop(options[:timeout] || @timeout)
  end
end

def initialize(options = {}, &block)
  raise ArgumentError, "Connection pool requires a block" unless block
  options = DEFAULTS.merge(options)
  @size = Integer(options.fetch(:size))
  @timeout = options.fetch(:timeout)
  @available = TimedStack.new(@size, &block)
  @key = :"pool-#{@available.object_id}"
  @key_count = :"pool-#{@available.object_id}-count"
  INSTANCES[self] = self if INSTANCES
end

def reload(&block)
  @available.shutdown(reload: true, &block)
end

def shutdown(&block)
  @available.shutdown(&block)
end

def with(options = {})
  Thread.handle_interrupt(Exception => :never) do
    conn = checkout(options)
    begin
      Thread.handle_interrupt(Exception => :immediate) do
        yield conn
      end
    ensure
      checkin
    end
  end
end