def pop
      begin
        return nil if @f.size == 0

        @f.seek(-@entry_bytes, IO::SEEK_END)
        bytes = @f.read(@entry_bytes)
        @f.truncate(@f.size - @entry_bytes)
        @f.flush
      rescue => e
        PEROBS.log.fatal "Cannot pop from stack file #{@file_name}: " +
          e.message
      end

      bytes
    end
def pop
      begin
        return nil if @f.size == 0

        @f.seek(-@entry_bytes, IO::SEEK_END)
        bytes = @f.read(@entry_bytes)
        @f.truncate(@f.size - @entry_bytes)
        @f.flush
      rescue => e
        PEROBS.log.fatal "Cannot pop from stack file #{@file_name}: " +
          e.message
      end

      bytes
    end
Pop the last entry from the stack file.
 @return [String or nil] Popped entry or nil if stack is already empty.