???????????￡????????

    ????????????????????к???????????????ū?????????????浽????????????????????????漰?????????????????????????????????????????????е????????????????
    ??1????CPU?μ?????
     ????г?????CPU???????????????????????????ж??????????????????????????????????ε?????Щ??????д????????????????????Щ?????????????????
    1???????????????
    2??????FIFO????
    3????????????????
    ?????????CPU?????????л????Щ????????????????????????楨?????????socket???????????????е????????????????????Щ?????С?????????????????????
    ??????????????linux??????????????????????task_struct????????????????????????????????????task_struct??linux 0.11????????????Щ?????

 struct task_struct {
 /* these are hardcoded - don't touch */
  long state; /* -1 unrunnable?? 0 runnable?? >0 stopped */
  long counter;
  long priority;
  long signal;
  struct sigaction sigaction[32];
  long blocked; /* bitmap of masked signals */
 /* various fields */
  int exit_code;
  unsigned long start_code??end_code??end_data??brk??start_stack;
  long pid??father??pgrp??session??leader;
  unsigned short uid??euid??suid;
  unsigned short gid??egid??sgid;
  long alarm;
  long utime??stime??cutime??cstime??start_time;
  unsigned short used_math;
 /* file system info */
  int tty;  /* -1 if no tty?? so it must be signed */
  unsigned short umask;
  struct m_inode * pwd;
  struct m_inode * root;
  struct m_inode * executable;
  unsigned long close_on_exec;
  struct file * filp[NR_OPEN];
 /* ldt for this task 0 - zero 1 - cs 2 - ds&ss */
  struct desc_struct ldt[3];
 /* tss for this task */
  struct tss_struct tss;
 };

    ????task?????????pid?????????????????????pid???д????????????????????????????????塣
    ????????????????????????task_struct?????????????壬??????????thread????????????????????thread????????????????????????????????????????????????????鷳?????????????????Щ????????????????????????????????
    ???????????????????????????????????????????????з????????Щ???????
    1?????????????
    2????????????->??????->???????
    3??д???????->??????->д??????
    ???д????????????????????

 #include <unistd.h>
 #include <stdio.h>
 
 int value = 10;
 
 int main(int argc?? char* argv[])
 {
     int pid = fork();
     if(!pid){
         Value = 12;
         return 0;
     }
     printf("value = %d "?? value);
     return 1;
 }