Thread間のデータ共有の仕組みについて

import core.thread;
import std.stdio;
import std.concurrency;

class Writer {
  public:
    this() {
      _tg = new ThreadGroup;
      _cnt = 0;
    }

    void write_tg(string text, int timeout) {
      _tg.create({
        while (1) {
          ++_cnt;
          writeln(_cnt);
          writeln(text);
          writeln();
          Thread.sleep(dur!"seconds"(timeout));
        }
      });
    }

    void write_spawn(string text, int timeout) {
      spawn(&write, text, timeout, _cnt);
    }

  private:
    ThreadGroup _tg;
    int _cnt;
}

void write(string text, int timeout, ref int cnt) {
  while (1) {
    ++cnt;
    writeln(cnt);
    writeln(text);
    writeln();
    Thread.sleep(dur!"seconds"(timeout));
  }
}

void main() {
  Writer writer = new Writer;

  /*
  writer.write_spawn("3秒毎spawn", 3);
  writer.write_spawn("1秒毎spawn", 1);
  writer.write_spawn("10秒毎spawn", 10);
  */
  /*
  writer.write_tg("3秒毎tg", 3);
  writer.write_tg("1秒毎tg", 1);
  writer.write_tg("10秒毎tg", 10);
  */
}