--- join
--- join(limit)  ruby 1.7 feature

    å self μ¹Ԥλޤǡȥåɤߤ
    ޤself 㳰ˤ꽪λƤС㳰ȥ
    åɤФȯޤ

    self ֤ޤ

    ruby 1.7 feature:  limit ꤹȡlimit äǥ
    Ȥnil ֤ޤ

    ʲϡ٤ƤΥåɤνλԤǤ

       threads = []
       threads.push(Thread.new { n = rand(5); sleep n; n })
       threads.push(Thread.new { n = rand(5); sleep n; n })
       threads.push(Thread.new { n = rand(5); sleep n; n })

       threads.each {|t| t.join}

