--- Process.setpriority(which, who, prio)

    ץץ롼ס桼θߤΥץ饤ƥ
    ꤷޤ(setpriority(2) [manual page] )

    Process ⥸塼 which ȤƻǤ 
    PRIO_PROCESS, PRIO_PGRP,
    PRIO_USER Ƥޤ

    who ˤϡwhich ͤˤäƥץ IDץ
    롼 ID桼 ID Τ줫ꤷޤ

    prio ˤϡ-20  20 ͤꤷޤ

    ץ饤ƥ 0 ֤ޤԤϡ
    㳰 Errno::EXXX ȯޤ

