code: func (p Process) Pid() (int, error) {
  	// math.MinInt32 is returned here, because it's invalid value
  	// for the kill() system call.
  	if p.ops == nil {
  		return math.MinInt32, newGenericError(fmt.Errorf("invalid process"), ProcessNotExecuted)
  	}
  	return p.ops.pid(), nil
  }
docs: // Pid returns the process ID