T1                  T2                        free=false;
----------------------------------------------   
while(free);        while(free);       進入?yún)^(qū)
free=true;          free=true;
----------------------------------------------
read(x);            read(x);           臨界區(qū)

if(x>=1)              if(x>=1)
   x=x-1;                x=x-1;

write(x);            write(x);
---------------------------------------------
free=false;           free=false;      退出區(qū)