實驗?zāi)康?/h1>

shell lab主要目的是為了熟悉進程控制和信號级乐。具體來說需要比對16個test和rtest文件的輸出阱洪，實現(xiàn)五個函數(shù)：

void eval(char *cmdline)：分析命令书释，并派生子進程執(zhí)行 主要功能是解析cmdline并運行
int builtin_cmd(char **argv)：解析和執(zhí)行bulidin命令，包括 quit, fg, bg, and jobs
void do_bgfg(char **argv) 執(zhí)行bg和fg命令
void waitfg(pid_t pid)：實現(xiàn)阻塞等待前臺程序運行結(jié)束
void sigchld_handler(int sig)：SIGCHID信號處理函數(shù)
void sigint_handler(int sig)：信號處理函數(shù)，響應(yīng) SIGINT (ctrl-c) 信號 
void sigtstp_handler(int sig)：信號處理函數(shù)圣猎，響應(yīng) SIGTSTP (ctrl-z) 信號

輔助函數(shù)

可用輔助函數(shù)：

• int parseline(const char *cmdline,char **argv)：獲取參數(shù)列表，返回是否為后臺運行命令
• void clearjob(struct job_t *job)：清除job結(jié)構(gòu)體乞而。
• void initjobs(struct job_t *jobs)：初始化jobs鏈表送悔。
• void maxjid(struct job_t *jobs)：返回jobs鏈表中最大的jid號。
• int addjob(struct job_t *jobs,pid_t pid,int state,char *cmdline)：在jobs鏈表中添加job
• int deletejob(struct job_t *jobs,pid_t pid)：在jobs鏈表中刪除pid的job爪模。
• pid_t fgpid(struct job_t *jobs)：返回當(dāng)前前臺運行job的pid號欠啤。
• struct job_t *getjobpid(struct job_t *jobs,pid_t pid)：返回pid號的job。
• struct job_t *getjobjid(struct job_t *jobs,int jid)：返回jid號的job屋灌。
• int pid2jid(pid_t pid)：將pid號轉(zhuǎn)化為jid洁段。
• void listjobs(struct job_t *jobs)：打印jobs。
• void sigquit_handler(int sig)：處理SIGQUIT信號共郭。

簡介

shell是交互式的命令行解釋器祠丝，打印提示符并在stdin上等待輸入命令，并按照命令行的內(nèi)容執(zhí)行除嘹。命令行是ASCII單詞組成的命令和參數(shù)序列写半。若首個單詞是內(nèi)置命令，shell會立即在當(dāng)前進程中執(zhí)行尉咕。否則是可執(zhí)行文件路徑叠蝇，shell派生出子進程，然后在該子進程的上下文中加載和運行程序年缎。解釋單個命令行而創(chuàng)建的子進程叫作業(yè)悔捶，通常由Unix管道連接的多個子進程組成。若命令行以&號“&”結(jié)束晦款，則作業(yè)將在后臺運行且不會等待作業(yè)結(jié)束炎功。否則作業(yè)將在前臺運行且等待作業(yè)終止。故在任何時間點最多僅一個作業(yè)在前臺運行缓溅。但可在后臺運行任意數(shù)量的作業(yè)蛇损。

例如：tsh> /bin/ls -l -d

在前臺運行程序，程序的入口是：int main(int argc,char *argv[])

則argc==3坛怪，argv[0] == ‘‘/bin/ls’’淤齐，argv[1]== ‘‘-l’’,argv[2]== ‘‘-d’’。若在命令行后加上&袜匿，則在后臺運行l(wèi)s程序更啄。shell支持作業(yè)控制，允許用戶在后臺和前臺移動作業(yè)居灯，并更改作業(yè)中進程的狀態(tài)（運行祭务、停止或終止）内狗。輸入ctrl-c會向前臺作業(yè)中的每個進程發(fā)送SIGINT信號，默認(rèn)操作是終止進程义锥。類似地柳沙，鍵入ctrl-z將向前臺作業(yè)中的每個進程發(fā)送SIGTSTP信號，默認(rèn)操作是將進程置于停止?fàn)顟B(tài)拌倍，直到收到SIGCONT信號將其喚醒赂鲤。當(dāng)然shell也提供內(nèi)置命令支持作業(yè)控制：

• jobs：列出運行和終止的后臺作業(yè)
• bg <job>：將終止的后臺作業(yè)改為運行
• fg <job>：將終止或運行的后臺作業(yè)改為前臺運行
• kill <job>：發(fā)送特定信號給特定進程和進程組，默認(rèn)動作是終止進程
• quit：終止shell

有三點值得注意：

• tsh不支持管道和I/O重定向
• 每個作業(yè)要么被process ID識別柱恤，要么被job ID識別数初，jid因該在命令行中用前綴“%”表示，“%5”表示jid 5梗顺，5表示PID 5
• shell因該回收所有僵尸進程泡孩，若任何一個作業(yè)因為接收到它沒有捕捉到的信號而終止，那么tsh應(yīng)該識別該事件荚守，并打印PID和錯誤描述消息

提示

• 仔細(xì)閱讀CSAPP第八章的異痴涞拢控制流和lab的writeup

• make testn測試shell執(zhí)行第n組測試數(shù)據(jù)的輸出，make rtestn打印shell預(yù)期輸出矗漾，tshref.out包含shell所有預(yù)期輸出結(jié)果锈候，先看文件輸出，了解命令格式再編碼敞贡，修改makefile文件中CFLAGS字段泵琳，加-g參數(shù)并去掉-O2參數(shù)

• waitpid, kill, fork,execve, setpgid, sigprocmask 很常用，可通過命令手冊查看使用細(xì)節(jié)誊役，WUNTRACED和WNOHANG選項對waitpid也很有用

• 實現(xiàn)信息處理函數(shù)获列，確保發(fā)送SIGINT和SIGTSTP信號給整個前臺進程組，用-pid代替pid作為kill參數(shù)

• 建議在waitfg的循環(huán)中用sleep函數(shù)蛔垢，在sigchld_handler中對waitpid只調(diào)用一次

• eval中進程在fork之前用sigprocmask阻塞SIGCHLD信號击孩，之后在解除信號阻塞，之后在調(diào)用addjob添加孩子到作業(yè)列表用sigprocmask阻塞信號鹏漆，因為子繼承繼承父進程的阻塞集合巩梢，所以子程序必須確保在執(zhí)行新進程前解除阻塞SIGCHLD信號。父進程需以這種方式阻塞SIGCHLD信號艺玲，避免在父進程調(diào)用addjob之前括蝠，SIGCHLD處理器獲取子進程(從而從任務(wù)列表中刪除)的競爭狀態(tài)。

• 不要直接調(diào)用常用命令饭聚，而應(yīng)輸入完整路徑忌警，如/bin/ls

• 當(dāng)在標(biāo)準(zhǔn)Unix shell運行tsh時，tsh運行在前臺進程組中秒梳。若tsh隨后創(chuàng)建子進程法绵，默認(rèn)情況下箕速，該子進程也是前臺進程組的成員。因為按下ctrl-c會向前臺組中的每個進程發(fā)送SIGINT信號礼烈，按下ctrl-c會向tsh及Unix shell創(chuàng)建的每個子進程弧满，顯然不正確婆跑。應(yīng)該在fork后此熬，但在execve前，子進程調(diào)用setpgid(0,0)滑进，把子進程放到新進程組中犀忱，該進程組ID與子進程的PID相同。確保前臺進程組中只有一個進程扶关，即tsh進程阴汇。當(dāng)按下ctrl-c時，tsh應(yīng)捕獲生成的SIGINT节槐，然后將其轉(zhuǎn)發(fā)給包含前臺作業(yè)的進程組搀庶。

實驗前環(huán)境配置

由于csapp都是運行在32位系統(tǒng)，即使安裝32位系統(tǒng)所需的庫铜异，仍然無法運行tsh哥倔，在網(wǎng)上找到有人配置好的csapp的docker鏡像，因此直接使用docker揍庄，環(huán)境配置如下：

1. 安裝docker咆蒿，并配置加速
2. 安裝vscode和ssh插件
3. 命令行中運行systemctl start docker啟動docker和docker run --privileged -d -p 1221:22 --name shell yansongsongsong/csapp:shelllabshell lab的實驗環(huán)境
4. 通過ssh輸入密碼登錄實驗環(huán)境

實驗

在vscode中打開shlab-handout文件夾，并打開tsh.c文件蚂子，可以看到在main函數(shù)中調(diào)用eval函數(shù)沃测，而在書P525或20-ecf-sigs的P19可找到eval函數(shù)的整體代碼框架：

void eval(char *cmdline) 
{
    char *argv[MAXARGS];/*Argument list execve() */
    char buf[MAXLINE];/*Holds modified command line */
    int bg;/*Should the job run in bg or fg? */
    pid_t pid;/*Process id */

    strcpy(buf, cmdline);
    bg = parseline(buf, argv);
    if (argv[0] == NULL)
        return;/* Ignore empty lines */

    if (!builtin_cmd(argv)) {
        if ((pid = Fork()) == 0) {/* Child runs user job */
            Execve(argv[0], argv, environ);
        }/* Parent waits for foreground job to terminate */
        if (!bg) {
            int status;
            if (waitpid(pid, &status,0) < 0)
                unix_error("waitfg: waitpid error");
        }
        else
            printf("%d %s", pid, cmdline);
    }
    return;
}

盡管ppt上說有bug，暫時先不管食茎，先搞好整體框架蒂破，完成簡單的函數(shù)，到后面在考慮别渔。另外值得一提的是這里將fork和execve都進行封裝以處理錯誤情況附迷。
運行make rtest01和make test01可以看到輸出一樣，已經(jīng)達到要求钠糊。同樣操作挟秤，可以看到test02未按照預(yù)期退出tsh，分析知需要實現(xiàn)builtin_cmd函數(shù)抄伍。同樣在書上P525能找到基礎(chǔ)代碼艘刚，只需加上jobs、fg截珍、bg3種情況即可攀甚。代碼如下：

int builtin_cmd(char **argv) 
{
    if(!strcmp(argv[0],"quit")) /* quit command */
        exit(0);

    if (!strcmp(argv[0], "&")) /* Ignore singleton & */
        return 1; 
    
    if(!strcmp((argv[0]),"jobs"))/* jobs command */
    {
        listjobs(jobs);
        return 1;
    }

    if(!strcmp((argv[0]),"fg") || !strcmp((argv[0]),"bg"))/* bg/fg command */
    {
        do_bgfg(argv);
        return 1;
    }
    return 0;     /* not a builtin command */
}

這樣就過了test02和test03箩朴，經(jīng)過比較test04和rtest04的輸出，確定只需修改輸出格式即可：

printf("[%d] (%d) %s", pid2jid(pid),pid, cmdline);

接著發(fā)現(xiàn)test05是執(zhí)行內(nèi)部命令：jobs秋度，打印job list炸庞，比對rtest05發(fā)現(xiàn)沒有打印出job，參考上面的提示第6條荚斯，知應(yīng)同步避免父子競爭埠居，具體來說：父進程在fork前屏蔽信號，子進程在execve前還原信號事期，因為子進程回繼承原來的屏蔽信號滥壕。同時前臺job需要調(diào)用waitfg進行等待。如果不阻塞會出現(xiàn)子進程先結(jié)束從jobs中刪除兽泣，然后再執(zhí)行到主進程addjob的競爭問題绎橘。在書上P542和PPT P57頁都有對應(yīng)的參考代碼：

int main(int argc, char **argv)
{
    int pid;
    sigset_t mask_all, mask_one, prev_one;
    int n = N; /* N = 5 */
    Sigfillset(&mask_all);
    Sigemptyset(&mask_one);
    Sigaddset(&mask_one, SIGCHLD);
    Signal(SIGCHLD, handler);
    initjobs(); /* Initialize the job list */
    
    while (n--) {
        Sigprocmask(SIG_BLOCK, &mask_one, &prev_one); /* Block SIGCHLD */
        if ((pid = Fork()) == 0) { /* Child process */
            Sigprocmask(SIG_SETMASK, &prev_one, NULL); /* Unblock SIGCHLD */
            Execve("/bin/date", argv, NULL);
        }
        Sigprocmask(SIG_BLOCK, &mask_all, NULL); /* Parent process */
        addjob(pid); /* Add the child to the job list */
        Sigprocmask(SIG_SETMASK, &prev_one, NULL); /* Unblock SIGCHLD */
    }
    exit(0);
}

加上圖中對應(yīng)代碼，同時若子進程結(jié)束唠倦，需要delete job称鳞，在sigchld_handler中加上非阻塞循環(huán)等待子進程的代碼：

void eval(char *cmdline) 
{
    char *argv[MAXARGS];/*Argument list execve() */
    char buf[MAXLINE];/*Holds modified command line */
    int bg;/*Should the job run in bg or fg? */
    pid_t pid;/*Process id */
    sigset_t mask_all,mask_one,prev_one;

    strcpy(buf, cmdline);
    bg = parseline(buf, argv);
    if (argv[0] == NULL)
        return;/* Ignore empty lines */

    if (!builtin_cmd(argv)) {
        Sigfillset(&mask_all);/* add every signal number to set */
        Sigemptyset(&mask_one);/* create empty set */
        Sigaddset(&mask_one, SIGCHLD);/* add signal number to set */

        /*  block SIGINT and save previous blocked set */
        Sigprocmask(SIG_BLOCK, &mask_one, &prev_one); /* Block SIGCHLD */
        if ((pid = Fork()) == 0) {/* Child runs user job */
            /* restore previous blocked set,unblocking SIGINT */
            Sigprocmask(SIG_SETMASK, &prev_one, NULL); /* Unblock SIGCHLD */
            //Setpgid(0,0);
            Execve(argv[0], argv, environ);
        }/* Parent waits for foreground job to terminate */

        Sigprocmask(SIG_BLOCK, &mask_all, NULL); /* Block SIGCHLD */
        int st = (bg==0) ? FG : BG;
        addjob(jobs,pid,st,cmdline);
        Sigprocmask(SIG_SETMASK, &prev_one, NULL); /* Unblock SIGCHLD */
        if (!bg) {
            //由于sigchld_handler上面被調(diào)用，而上面回調(diào)用waitpid稠鼻，因此這里不用調(diào)用只需循環(huán)等待即可
            waitfg(pid);
        }
        else
            printf("[%d] (%d) %s", pid2jid(pid),pid, cmdline);
    }
    return;
}

void sigchld_handler(int sig) 
{
    int olderrno = errno;
    sigset_t mask_all,prev_all;
    pid_t pid;
    Sigfillset(&mask_all);
    /*改成非阻塞冈止，否則test05中運行到此處，前端進程執(zhí)行jobs會阻塞直到所有子進程都被回收枷餐，即兩個后端進程都執(zhí)行并delete才會離開靶瘸，則jobs命令什么也沒有打印*/
    while((pid = waitpid(-1,NULL,WNOHANG | WUNTRACED))>0){
        Sigprocmask(SIG_BLOCK,&mask_all,&prev_all);
        deletejob(jobs,pid);
        Sigprocmask(SIG_SETMASK,&prev_all,NULL);
    }
    errno = olderrno;
    return;
}

如果是前臺命令，則調(diào)用waitfg循環(huán)等待毛肋，在注釋中看到最好不要用waitpid(pid,NULL,0)怨咪，其次根據(jù)上面的提示，不要同時在sigchld_handler和waitfg函數(shù)中使用waitpid润匙，因為在同一個程序的兩個地方都回收僵死進程诗眨，雖然也行，但容易讓人迷惑：

void waitfg(pid_t pid)
{
    while(fgpid(jobs))
        usleep(1000);//一秒
    return;
}

這樣就完成test05孕讳，接下來test06和test07匠楚、test08就是實現(xiàn)SIGINT和SIGSTOP信號處理函數(shù)，注意前面提示的第4條用-pid作為kill的參數(shù)厂财，同時最后一條在fork后execve前子進程應(yīng)調(diào)用setpgid(0,0)芋簿，否則回報錯No such process，注意sigint_handler和sigtstp_handler只需調(diào)用kill即可璃饱，將輸出留到sigchld_handler中与斤，這樣就需修改前面的sigchld_handler以處理不同子進程退出狀態(tài)：

void sigint_handler(int sig) 
{
    int olderrno = errno;
    pid_t fg = fgpid(jobs);
    if(fg){
        Kill(-fg,sig);
    }
    errno = olderrno;
    return;
}
void sigtstp_handler(int sig) 
{
    int olderrno = errno;
    pid_t fg = fgpid(jobs);
    if(fg){
        Kill(-fg,sig);
    }
    errno = olderrno;
    return;
}

void sigchld_handler(int sig) 
{
    int olderrno = errno;
    sigset_t mask_all,prev;
    pid_t pid;
    int status;
    Sigfillset(&mask_all);
    /*改成非阻塞，否則test05中運行到此處，前端進程執(zhí)行jobs會阻塞直到所有子進程都被回收撩穿，即兩個后端進程都執(zhí)行并delete才會離開磷支，則jobs命令什么也沒有打印*/
    while((pid = waitpid(-1,&status,WNOHANG | WUNTRACED))>0){
        // WNOHANG | WUNTRACED 是立即返回
        // 用WIFEXITED(status)，WIFSIGNALED(status)食寡，WIFSTOPPED(status)等來補獲終止或者
        // 被停止的子進程的退出狀態(tài)雾狈。
        if (WIFEXITED(status))  // 正常退出 delete
        {
            sigprocmask(SIG_BLOCK, &mask_all, &prev);
            deletejob(jobs, pid);
            sigprocmask(SIG_SETMASK, &prev, NULL);
        }
        else if (WIFSIGNALED(status))  // 信號退出 delete
        {
            struct job_t* job = getjobpid(jobs, pid);
            sigprocmask(SIG_BLOCK, &mask_all, &prev);
            printf("Job [%d] (%d) terminated by signal %d\n", job->jid, job->pid, WTERMSIG(status));
            deletejob(jobs, pid);
            sigprocmask(SIG_SETMASK, &prev, NULL);
        }
        else  // 停止 只修改狀態(tài)就行
        {
            struct job_t* job = getjobpid(jobs, pid);
            sigprocmask(SIG_BLOCK, &mask_all, &prev);
            printf("Job [%d] (%d) stopped by signal %d\n", job->jid, job->pid, WSTOPSIG(status));
            job->state= ST;
            sigprocmask(SIG_SETMASK, &prev, NULL);
        }
    }
    errno = olderrno;  // 恢復(fù)
    return;
}

這樣就完成test06和test07、test08抵皱。接下來test09和test10是測試fg和bg內(nèi)置命令善榛，先解析命令通過getjobjid或getjobpid獲取job，再分情況對fg和bg命令做不同處理叨叙，輸入%num 代表任務(wù)id锭弊，num代表進程id，分情況討論即可擂错，但要注意各種異常情況：

void do_bgfg(char **argv) 
{
    if(!argv[1]){
        printf("%s command requires PID or %%jobid argument\n", argv[0]);
        return;
    }

    if (!isdigit(argv[1][0]) && argv[1][0] != '%') {            // Checks if the second argument is valid
        printf("%s: argument must be a PID or %%jobid\n", argv[0]);
        return;
    }

    struct job_t* myjob;
    if(argv[1][0]=='%'){
        myjob = getjobjid(jobs,atoi(&argv[1][1]));
        if(!myjob){
            printf("%s: No such job\n", argv[1]);
            return;
        }
    }else{
        myjob = getjobpid(jobs,atoi(argv[1]));
        if (!myjob) {                                 // Checks if the given PID is there
            printf("(%d): No such process\n", atoi(argv[1]));
            return;
        }
    }

    Kill(-myjob->pid,SIGCONT);
    if(!strcmp(argv[0],"bg")){
        myjob->state = BG;
        printf("[%d] (%d) %s",myjob->jid,myjob->pid,myjob->cmdline);
    }else{
        myjob->state = FG;
        waitfg(myjob->pid);
    }

    return;
}

這樣就過了test09和test10。接下來test11 和test12 樱蛤、test13分別測試Forward SIGINT钮呀、Forward SIGTSTP、Restart stopped process都能正常通過昨凡，若每通過爽醋，因該是前面某些測試有問題，解決后即可便脊。test14是測試JID或PID的錯誤輸入的情況蚂四，較容易通過。test15將前面所有測試情況放一起哪痰，也順利通過遂赠，而test16是測試tsh能否處理不是來自終端而是來自其他進程的SIGSTP和SIGINT信號，順利通過晌杰。

總結(jié)

最終代碼見下跷睦，該實驗主要涉及加載、進程控制肋演、信號等基礎(chǔ)但很重要的知識抑诸，涉及到異常控制流爹殊、進程蜕乡、系統(tǒng)調(diào)用、信號處理函數(shù)與非本地跳轉(zhuǎn)等并發(fā)編程的知識。并發(fā)的同步問題是關(guān)鍵挑胸，利用信號屏蔽與還原就能解決狠角。此外閱讀 man 手冊了解系統(tǒng)接口使用細(xì)節(jié)對完成實驗很有幫助巴碗。

/* 
 * tsh - A tiny shell program with job control
 * 
 * <Put your name and login ID here>
 */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <errno.h>

/* Misc manifest constants */
#define MAXLINE    1024   /* max line size */
#define MAXARGS     128   /* max args on a command line */
#define MAXJOBS      16   /* max jobs at any point in time */
#define MAXJID    1<<16   /* max job ID */

/* Job states */
#define UNDEF 0 /* undefined */
#define FG 1    /* running in foreground */
#define BG 2    /* running in background */
#define ST 3    /* stopped */

/* 
 * Jobs states: FG (foreground), BG (background), ST (stopped)
 * Job state transitions and enabling actions:
 *     FG -> ST  : ctrl-z
 *     ST -> FG  : fg command
 *     ST -> BG  : bg command
 *     BG -> FG  : fg command
 * At most 1 job can be in the FG state.
 */

/* Global variables */
extern char **environ;      /* defined in libc */
char prompt[] = "tsh> ";    /* command line prompt (DO NOT CHANGE) */
int verbose = 0;            /* if true, print additional output */
int nextjid = 1;            /* next job ID to allocate */
char sbuf[MAXLINE];         /* for composing sprintf messages */

struct job_t {              /* The job struct */
    pid_t pid;              /* job PID */
    int jid;                /* job ID [1, 2, ...] */
    int state;              /* UNDEF, BG, FG, or ST */
    char cmdline[MAXLINE];  /* command line */
};
struct job_t jobs[MAXJOBS]; /* The job list */
/* End global variables */

/*error handling function */
pid_t Fork(void);
void Execve(const char *filename, char *const argv[], char *const environ[]);
void Kill(pid_t pid, int signum);
void Sigemptyset(sigset_t *set);
void Sigaddset(sigset_t *set, int signum);
void Sigfillset(sigset_t *set);
void Setpgid(pid_t pid, pid_t pgid);
void Sigprocmask(int how, sigset_t *set, sigset_t *oldset);
/* Function prototypes */

/* Here are the functions that you will implement */
void eval(char *cmdline);
int builtin_cmd(char **argv);
void do_bgfg(char **argv);
void waitfg(pid_t pid);

void sigchld_handler(int sig);
void sigtstp_handler(int sig);
void sigint_handler(int sig);

/* Here are helper routines that we've provided for you */
int parseline(const char *cmdline, char **argv); 
void sigquit_handler(int sig);

void clearjob(struct job_t *job);
void initjobs(struct job_t *jobs);
int maxjid(struct job_t *jobs); 
int addjob(struct job_t *jobs, pid_t pid, int state, char *cmdline);
int deletejob(struct job_t *jobs, pid_t pid); 
pid_t fgpid(struct job_t *jobs);
struct job_t *getjobpid(struct job_t *jobs, pid_t pid);
struct job_t *getjobjid(struct job_t *jobs, int jid); 
int pid2jid(pid_t pid); 
void listjobs(struct job_t *jobs);

void usage(void);
void unix_error(char *msg);
void app_error(char *msg);
typedef void handler_t(int);
handler_t *Signal(int signum, handler_t *handler);

/*
 * main - The shell's main routine 
 */
int main(int argc, char **argv) 
{
    char c;
    char cmdline[MAXLINE];
    int emit_prompt = 1; /* emit prompt (default) */

    /* Redirect stderr to stdout (so that driver will get all output
     * on the pipe connected to stdout) */
    dup2(1, 2);

    /* Parse the command line */
    while ((c = getopt(argc, argv, "hvp")) != EOF) {
        switch (c) {
        case 'h':             /* print help message */
            usage();
        break;
        case 'v':             /* emit additional diagnostic info */
            verbose = 1;
        break;
        case 'p':             /* don't print a prompt */
            emit_prompt = 0;  /* handy for automatic testing */
        break;
    default:
            usage();
    }
    }

    /* Install the signal handlers */

    /* These are the ones you will need to implement */
    Signal(SIGINT,  sigint_handler);   /* ctrl-c */
    Signal(SIGTSTP, sigtstp_handler);  /* ctrl-z */
    Signal(SIGCHLD, sigchld_handler);  /* Terminated or stopped child */

    /* This one provides a clean way to kill the shell */
    Signal(SIGQUIT, sigquit_handler); 

    /* Initialize the job list */
    initjobs(jobs);

    /* Execute the shell's read/eval loop */
    while (1) {

    /* Read command line */
    if (emit_prompt) {
        printf("%s", prompt);
        fflush(stdout);
    }
    if ((fgets(cmdline, MAXLINE, stdin) == NULL) && ferror(stdin))
        app_error("fgets error");
    if (feof(stdin)) { /* End of file (ctrl-d) */
        fflush(stdout);
        exit(0);
    }

    /* Evaluate the command line */
    eval(cmdline);
    fflush(stdout);
    fflush(stdout);
    } 

    exit(0); /* control never reaches here */
}
  
/* 
 * eval - Evaluate the command line that the user has just typed in
 * 
 * If the user has requested a built-in command (quit, jobs, bg or fg)
 * then execute it immediately. Otherwise, fork a child process and
 * run the job in the context of the child. If the job is running in
 * the foreground, wait for it to terminate and then return.  Note:
 * each child process must have a unique process group ID so that our
 * background children don't receive SIGINT (SIGTSTP) from the kernel
 * when we type ctrl-c (ctrl-z) at the keyboard.  
*/
void eval(char *cmdline) 
{
    char *argv[MAXARGS];/*Argument list execve() */
    char buf[MAXLINE];/*Holds modified command line */
    int bg;/*Should the job run in bg or fg? */
    pid_t pid;/*Process id */
    sigset_t mask_all,mask_one,prev_one;

    strcpy(buf, cmdline);
    bg = parseline(buf, argv);
    if (argv[0] == NULL)
        return;/* Ignore empty lines */

    if (!builtin_cmd(argv)) {
        //blocking SIGCHLD in if status,otherewise it maybe has bugs
        Sigfillset(&mask_all);/* add every signal number to set */
        Sigemptyset(&mask_one);/* create empty set */
        Sigaddset(&mask_one, SIGCHLD);/* add signal number to set */

        /*  block SIGINT and save previous blocked set */
        /* avoid parent process run to addjob exited,before fork child process block sigchild signal,after call addjob unblock  */
        Sigprocmask(SIG_BLOCK, &mask_one, &prev_one); /* Block SIGCHLD */
        if ((pid = Fork()) == 0) {/* Child runs user job */
            /* restore previous blocked set,unblocking SIGINT */
            /* child process inherit parent process' blocking sets,avoid it can't receive itself child process signal,so we must unblock */
            Sigprocmask(SIG_SETMASK, &prev_one, NULL); /* Unblock SIGCHLD */
            Setpgid(0,0);// set child's group to a new process group (this is identical to the child's PID)
            Execve(argv[0], argv, environ);//this function not return ,so must call exit,otherewise it will run forever
        }/* Parent waits for foreground job to terminate */

        Sigprocmask(SIG_BLOCK, &mask_all, NULL); /* Block SIGCHLD */
        int st = (bg==0) ? FG : BG;
        addjob(jobs,pid,st,cmdline);
        Sigprocmask(SIG_SETMASK, &prev_one, NULL); /* Unblock SIGCHLD */
        if (!bg) {
            //because sigchld_handler was called above称簿，it call waitpid扣癣，so don't call and circular wait wait
            waitfg(pid);
        }
        else
            printf("[%d] (%d) %s", pid2jid(pid),pid, cmdline);
    }
    return;
}

/* 
 * parseline - Parse the command line and build the argv array.
 * 
 * Characters enclosed in single quotes are treated as a single
 * argument.  Return true if the user has requested a BG job, false if
 * the user has requested a FG job.  
 */
int parseline(const char *cmdline, char **argv) 
{
    static char array[MAXLINE]; /* holds local copy of command line */
    char *buf = array;          /* ptr that traverses command line */
    char *delim;                /* points to first space delimiter */
    int argc;                   /* number of args */
    int bg;                     /* background job? */

    strcpy(buf, cmdline);
    buf[strlen(buf)-1] = ' ';  /* replace trailing '\n' with space */
    while (*buf && (*buf == ' ')) /* ignore leading spaces */
    buf++;

    /* Build the argv list */
    argc = 0;
    if (*buf == '\'') {
    buf++;
    delim = strchr(buf, '\'');
    }
    else {
    delim = strchr(buf, ' ');
    }

    while (delim) {
    argv[argc++] = buf;
    *delim = '\0';
    buf = delim + 1;
    while (*buf && (*buf == ' ')) /* ignore spaces */
           buf++;

    if (*buf == '\'') {
        buf++;
        delim = strchr(buf, '\'');
    }
    else {
        delim = strchr(buf, ' ');
    }
    }
    argv[argc] = NULL;
    
    if (argc == 0)  /* ignore blank line */
    return 1;

    /* should the job run in the background? */
    if ((bg = (*argv[argc-1] == '&')) != 0) {
    argv[--argc] = NULL;
    }
    return bg;
}

/* 
 * builtin_cmd - If the user has typed a built-in command then execute
 *    it immediately.  
 */
int builtin_cmd(char **argv) 
{
    if(!strcmp(argv[0],"quit")) /* quit command */
        exit(0);

    if (!strcmp(argv[0], "&")) /* Ignore singleton & */
        return 1; 
    
    if(!strcmp((argv[0]),"jobs"))/* jobs command */
    {
        listjobs(jobs);
        return 1;
    }

    if(!strcmp((argv[0]),"fg") || !strcmp((argv[0]),"bg"))/* bg/fg command */
    {
        do_bgfg(argv);
        return 1;
    }
    return 0;     /* not a builtin command */
}

/* 
 * do_bgfg - Execute the builtin bg and fg commands
 */
void do_bgfg(char **argv) 
{
    if(!argv[1]){
        printf("%s command requires PID or %%jobid argument\n", argv[0]);
        return;
    }

    if (!isdigit(argv[1][0]) && argv[1][0] != '%') {            // Checks if the second argument is valid
        printf("%s: argument must be a PID or %%jobid\n", argv[0]);
        return;
    }

    struct job_t* myjob;
    if(argv[1][0]=='%'){//jid
        myjob = getjobjid(jobs,atoi(&argv[1][1]));
        if(!myjob){
            printf("%s: No such job\n", argv[1]);
            return;
        }
    }else{//pid
        myjob = getjobpid(jobs,atoi(argv[1]));
        if (!myjob) {                                 // Checks if the given PID is there
            printf("(%d): No such process\n", atoi(argv[1]));
            return;
        }
    }

    Kill(-myjob->pid,SIGCONT);//send continue signal 
    if(!strcmp(argv[0],"bg")){
        myjob->state = BG;
        printf("[%d] (%d) %s",myjob->jid,myjob->pid,myjob->cmdline);
    }else{
        myjob->state = FG;
        waitfg(myjob->pid);
    }

    return;
}

/* 
 * waitfg - Block until process pid is no longer the foreground process
 */
void waitfg(pid_t pid)
{
    while(fgpid(jobs))
        usleep(1000);//sleep one second
    return;
}

/*****************
 * Signal handlers
 *****************/

/* 
 * sigchld_handler - The kernel sends a SIGCHLD to the shell whenever
 *     a child job terminates (becomes a zombie), or stops because it
 *     received a SIGSTOP or SIGTSTP signal. The handler reaps all
 *     available zombie children, but doesn't wait for any other
 *     currently running children to terminate.  
 */
void sigchld_handler(int sig) 
{
    int olderrno = errno;
    sigset_t mask_all,prev;
    pid_t pid;
    int status;
    Sigfillset(&mask_all);
    while((pid = waitpid(-1,&status,WNOHANG | WUNTRACED))>0){
        // WNOHANG | WUNTRACED return immediately
        if (WIFEXITED(status))  // normally exited,delete job
        {
            sigprocmask(SIG_BLOCK, &mask_all, &prev);
            deletejob(jobs, pid);
            sigprocmask(SIG_SETMASK, &prev, NULL);
        }
        else if (WIFSIGNALED(status))  //terminated by signal, delete job and print message
        {
            struct job_t* job = getjobpid(jobs, pid);
            sigprocmask(SIG_BLOCK, &mask_all, &prev);
            printf("Job [%d] (%d) terminated by signal %d\n", job->jid, job->pid, WTERMSIG(status));
            deletejob(jobs, pid);
            sigprocmask(SIG_SETMASK, &prev, NULL);
        }
        else  //stopped,change the status
        {
            struct job_t* job = getjobpid(jobs, pid);
            sigprocmask(SIG_BLOCK, &mask_all, &prev);
            printf("Job [%d] (%d) stopped by signal %d\n", job->jid, job->pid, WSTOPSIG(status));
            job->state= ST;
            sigprocmask(SIG_SETMASK, &prev, NULL);
        }
        //actually there is WIFCONTINUED,but we don't care about
    }
    errno = olderrno;  
    return;
}

/* 
 * sigint_handler - The kernel sends a SIGINT to the shell whenver the
 *    user types ctrl-c at the keyboard.  Catch it and send it along
 *    to the foreground job.  
 */
void sigint_handler(int sig) 
{
    int olderrno = errno;
    pid_t fg = fgpid(jobs);
    if(fg){
        Kill(-fg,sig);
    }
    errno = olderrno;
    return;
}

/*
 * sigtstp_handler - The kernel sends a SIGTSTP to the shell whenever
 *     the user types ctrl-z at the keyboard. Catch it and suspend the
 *     foreground job by sending it a SIGTSTP.  
 */
void sigtstp_handler(int sig) 
{
    int olderrno = errno;
    pid_t fg = fgpid(jobs);
    if(fg){
        Kill(-fg,sig);
    }
    errno = olderrno;
    return;
}

/*********************
 * End signal handlers
 *********************/

/***********************************************
 * Helper routines that manipulate the job list
 **********************************************/

/* clearjob - Clear the entries in a job struct */
void clearjob(struct job_t *job) {
    job->pid = 0;
    job->jid = 0;
    job->state = UNDEF;
    job->cmdline[0] = '\0';
}

/* initjobs - Initialize the job list */
void initjobs(struct job_t *jobs) {
    int i;

    for (i = 0; i < MAXJOBS; i++)
    clearjob(&jobs[i]);
}

/* maxjid - Returns largest allocated job ID */
int maxjid(struct job_t *jobs) 
{
    int i, max=0;

    for (i = 0; i < MAXJOBS; i++)
    if (jobs[i].jid > max)
        max = jobs[i].jid;
    return max;
}

/* addjob - Add a job to the job list */
int addjob(struct job_t *jobs, pid_t pid, int state, char *cmdline) 
{
    int i;
    
    if (pid < 1)
    return 0;

    for (i = 0; i < MAXJOBS; i++) {
    if (jobs[i].pid == 0) {
        jobs[i].pid = pid;
        jobs[i].state = state;
        jobs[i].jid = nextjid++;
        if (nextjid > MAXJOBS)
        nextjid = 1;
        strcpy(jobs[i].cmdline, cmdline);
        if(verbose){
            printf("Added job [%d] %d %s\n", jobs[i].jid, jobs[i].pid, jobs[i].cmdline);
            }
            return 1;
    }
    }
    printf("Tried to create too many jobs\n");
    return 0;
}

/* deletejob - Delete a job whose PID=pid from the job list */
int deletejob(struct job_t *jobs, pid_t pid) 
{
    int i;

    if (pid < 1)
        return 0;

    for (i = 0; i < MAXJOBS; i++) {
        if (jobs[i].pid == pid) {
            clearjob(&jobs[i]);
            nextjid = maxjid(jobs)+1;
            return 1;
        }
    }
    return 0;
}

/* fgpid - Return PID of current foreground job, 0 if no such job */
pid_t fgpid(struct job_t *jobs) {
    int i;

    for (i = 0; i < MAXJOBS; i++)
    if (jobs[i].state == FG)
        return jobs[i].pid;
    return 0;
}

/* getjobpid  - Find a job (by PID) on the job list */
struct job_t *getjobpid(struct job_t *jobs, pid_t pid) {
    int i;

    if (pid < 1)
    return NULL;
    for (i = 0; i < MAXJOBS; i++)
    if (jobs[i].pid == pid)
        return &jobs[i];
    return NULL;
}

/* getjobjid  - Find a job (by JID) on the job list */
struct job_t *getjobjid(struct job_t *jobs, int jid) 
{
    int i;

    if (jid < 1)
    return NULL;
    for (i = 0; i < MAXJOBS; i++)
    if (jobs[i].jid == jid)
        return &jobs[i];
    return NULL;
}

/* pid2jid - Map process ID to job ID */
int pid2jid(pid_t pid) 
{
    int i;

    if (pid < 1)
    return 0;
    for (i = 0; i < MAXJOBS; i++)
    if (jobs[i].pid == pid) {
            return jobs[i].jid;
        }
    return 0;
}

/* listjobs - Print the job list */
void listjobs(struct job_t *jobs) 
{
    int i;
    
    for (i = 0; i < MAXJOBS; i++) {
    if (jobs[i].pid != 0) {
        printf("[%d] (%d) ", jobs[i].jid, jobs[i].pid);
        switch (jobs[i].state) {
        case BG: 
            printf("Running ");
            break;
        case FG: 
            printf("Foreground ");
            break;
        case ST: 
            printf("Stopped ");
            break;
        default:
            printf("listjobs: Internal error: job[%d].state=%d ", 
               i, jobs[i].state);
        }
        printf("%s", jobs[i].cmdline);
    }
    }
}
/******************************
 * end job list helper routines
 ******************************/


/***********************
 * Other helper routines
 ***********************/

/*
 * usage - print a help message
 */
void usage(void) 
{
    printf("Usage: shell [-hvp]\n");
    printf("   -h   print this message\n");
    printf("   -v   print additional diagnostic information\n");
    printf("   -p   do not emit a command prompt\n");
    exit(1);
}

/*
 * unix_error - unix-style error routine
 */
void unix_error(char *msg)
{
    fprintf(stdout, "%s: %s\n", msg, strerror(errno));
    exit(1);
}

/*
 * app_error - application-style error routine
 */
void app_error(char *msg)
{
    fprintf(stdout, "%s\n", msg);
    exit(1);
}

/*
 * Signal - wrapper for the sigaction function
 */
handler_t *Signal(int signum, handler_t *handler) 
{
    struct sigaction action, old_action;

    action.sa_handler = handler;  
    sigemptyset(&action.sa_mask); /* block sigs of type being handled */
    action.sa_flags = SA_RESTART; /* restart syscalls if possible */

    if (sigaction(signum, &action, &old_action) < 0)
    unix_error("Signal error");
    return (old_action.sa_handler);
}

/*
 * sigquit_handler - The driver program can gracefully terminate the
 *    child shell by sending it a SIGQUIT signal.
 */
void sigquit_handler(int sig) 
{
    printf("Terminating after receipt of SIGQUIT signal\n");
    exit(1);
}

/******************************
 * my functions with error handling
 ******************************/

/*
 * fork error handling
 */
pid_t Fork(void)
{
    pid_t pid;

    if ((pid = fork()) < 0)
        unix_error("Fork error");
    return pid;
}

/*
 * execve error handling
 */
void Execve(const char *filename, char *const argv[], char *const environ[])
{
    if (execve(filename, argv, environ) < 0) {
        printf("%s: Command not found.\n", argv[0]);
        exit(0);
    }
}

/*
 * kill error handling
 */
void Kill(pid_t pid, int signum) 
{
    int kr;

    if ((kr = kill(pid, signum)) < 0)
        unix_error("Kill error");
    return;
}

/*
 * sigemptyset error handling
 */
void Sigemptyset(sigset_t *set)
{
    if(sigemptyset(set)<0)
        unix_error("Sigemptyset error");
    return;
}
/*
 * sigaddset error handling
 */
void Sigaddset(sigset_t *set,int sign)
{
    if(sigaddset(set,sign)<0)
        unix_error("Sigaddset error");
    return;
}

/*
 * sigprocmask error handling
 */ 
void Sigprocmask(int how, sigset_t *set, sigset_t *oldset)
{
    if(sigprocmask(how,set,oldset)<0)
        unix_error("Sigprocmask error");
    return;
}

/*
 * sigfillset error handling
 */
void Sigfillset(sigset_t *set)
{
    if(sigfillset(set)<0)
        unix_error("Sigfillset error");
    return;
}

/*
 * setpgid error handling
 */
void Setpgid(pid_t pid, pid_t pgid) {
    int rc;

    if ((rc = setpgid(pid, pgid)) < 0)
        unix_error("Setpgid error");
    return;
}

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