--- Process.waitpid(pid[, flags])
--- Process.waitpid2(pid[, flags])

    pid ǻꤵλҥץνλԤΥץ
    λ pid ֤ޤҥץ¸ߤʤ㳰 
    Errno::ECHILD [Errno::EXXX] ȯޤ

    flags ˤϡProcess ⥸塼 
    WNOHANG(Υ֥å󥰥⡼)
    WUNTRACED ¤ꤷޤάȤͤ 0 
    Ǥ

    Υ֥å󥰥⡼ɤǻҥץޤλƤʤˤ 
    nil ֤ޤwaitpid(2) [manual page]  
    wait4(2) [manual page] μƤʤޥǤ 
    flags ϤĤ nil ޤ 0 ꤹɬפޤ

    waitpid2 ϡͤ pid  $? 
    Ǥۤʤޤ

    ruby 1.7 feature:
    version 1.7  $?  Process::Status ֥
    Ǥ

