Re: [理工] [OS] 97台大電機

[wheels ()]

※ 引述《mqazz1 (無法顯示)》之銘言：
: suppose we have two processes with indices 0 and 1. Assume that count is a
: shared variable between the two processes with initial value zero. (Suppose
: count is implemented without limit in its range.) Also each process with index
: p has a local variable ticket[p] with initial value zero We have the following
: mutual-exclusion algorithm for the two processes in a distributed system.
:         while(ture){
:                 ticket[p] = count = count+1;
:                 while(ticket[1-p] != 0  &&  ticket[1-p] < ticket[p]);
                            我覺得問題是出在這^^^^^^^^^^^^^^^^^^^^^^^^

          如果兩個process都抓到相同的ticket值的話

          這一行while loop的判斷中  ticket[1-p] < ticket[p]一定不成立

          那麼不論AND任何值都會為FALSE  此while loop的condition一定為false

          則沒有人會進busy waiting就都跑到CS裡了

          所以應該是不滿足mutual-exclusion才對0.0

:                         CS
:                 ticket[p] = 0;
:                         RS
:         }
: 請問這分別滿足mutual exclusion, progress, bounded waiting嗎?
: 97台大電機

--
※ 發信站: 批踢踢實業坊(ptt.cc) 
◆ From: 114.24.175.65
→ wheels:但是若加入atomic的話請看前一篇B大的解法！