1 struct task_struct 
 2 /* these are hardcoded - don\'t touch */
 3     long state;        //任务的运行状态，-1 不可运行, 0 可运行（就绪）, >0 已停止
 4     long counter;    //任务运行时间计数
 5     long priority;
 6     long signal;
 7     struct sigaction sigaction[32];
 8     long blocked;    /* bitmap of masked signals */
 9 /* various fields */
10     int exit_code;
11     unsigned long start_code,end_code,end_data,brk,start_stack;
12     long pid,pgrp,session,leader;    //从左到右依次为：进程标识号（进程号）、进程组号、会话号、会话首领
13     int    groups[NGROUPS];    //进程所属组号，一个进程可以属于多个组
14     /* 
15      * pointers to parent process, youngest child, younger sibling,
16      * older sibling, respectively.  (p->father can be replaced with 
17      * p->p_pptr->pid)
18      */
19     //从左到右：指向父进程的指针、指向最新子进程的指针、指向比自己后创建的相邻进程的指针、指向比自己早创建的相邻进程的指针。
20     struct task_struct    *p_pptr, *p_cptr, *p_ysptr, *p_osptr;
21     unsigned short uid,euid,suid;
22     unsigned short gid,egid,sgid;
23     unsigned long timeout,alarm;
24     long utime,stime,cutime,cstime,start_time;
25     struct rlimit rlim[RLIM_NLIMITS]; 
26     unsigned int flags;    /* per process flags, defined below */
27     unsigned short used_math;
28 /* file system info */
29     int tty;        /* -1 if no tty, so it must be signed */
30     unsigned short umask;
31     struct m_inode * pwd;
32     struct m_inode * root;
33     struct m_inode * executable;
34     struct m_inode * library;
35     unsigned long close_on_exec;
36     struct file * filp[NR_OPEN];
37 /* ldt for this task 0 - zero 1 - cs 2 - ds&ss */
38     struct desc_struct ldt[3];
39 /* tss for this task */
40     struct tss_struct tss;
41 ;

1 //这里定义了进程运行时可能处于的状态
2 #define TASK_RUNNING            　　   0  //进程正在运行或已准备就绪
3 #define TASK_INTERRUPTIBLE　　   1  //进程处于可中断等待状态
4 #define TASK_UNINTERRUPTIBLE     2  //进程处于不可中断等待状态，主要用于I/O操作等待
5 #define TASK_ZOMBIE                          3  //进程处于僵死状态，已经停止运行，但父进程还没发信号。
6 #define TASK_STOPPED                        4  //进程已停止

 1 void schedule(void)
 2 
 3     int i,next,c;
 4     struct task_struct ** p;  //任务结构指针的指针
 5 
 6 /* check alarm, wake up any interruptible tasks that have got a signal */
 7 
 8     for(p = &LAST_TASK ; p > &FIRST_TASK ; --p)
 9         if (*p) 
10             if ((*p)->timeout && (*p)->timeout < jiffies) 
11                 (*p)->timeout = 0;
12                 if ((*p)->state == TASK_INTERRUPTIBLE)
13                     (*p)->state = TASK_RUNNING;
14             
15             if ((*p)->alarm && (*p)->alarm < jiffies) 
16                 (*p)->signal |= (1<<(SIGALRM-1));
17                 (*p)->alarm = 0;
18             
19             if (((*p)->signal & ~(_BLOCKABLE & (*p)->blocked)) &&
20             (*p)->state==TASK_INTERRUPTIBLE)
21                 (*p)->state=TASK_RUNNING;
22         
23 
24 /* this is the scheduler proper: */
25 //-------------------这是调度程序的主要部分-------------------
26     while (1) 
27         c = -1;
28         next = 0;
29         i = NR_TASKS;
30         p = &task[NR_TASKS];
31         while (--i) 
32             if (!*--p)
33                 continue;
34             if ((*p)->state == TASK_RUNNING && (*p)->counter > c)
35                 c = (*p)->counter, next = i;
36         
37         if (c) break;
38         for(p = &LAST_TASK ; p > &FIRST_TASK ; --p)
39             if (*p)
40                 (*p)->counter = ((*p)->counter >> 1) +
41                         (*p)->priority;
42     
43     switch_to(next);
44