flush_write_buffer

# File actioncable/lib/action_cable/connection/stream.rb, line 70
      def flush_write_buffer
        @write_lock.synchronize do
          loop do
            if @write_head.nil?
              return true if @write_buffer.empty?
              @write_head = @write_buffer.pop
            end

            written = @rack_hijack_io.write_nonblock(@write_head, exception: false)
            case written
            when :wait_writable
              return false
            when @write_head.bytesize
              @write_head = nil
            else
              @write_head = @write_head.byteslice(written, @write_head.bytesize)
              return false
            end
          end
        end
      end