csapp之lab：shell lab

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2022-02-02

实验目的

shell lab主要目的是为了熟悉进程控制和信号。具体来说需要比对16个test和rtest文件的输出，实现五个函数：

void eval(char *cmdline)：分析命令，并派生子进程执行 主要功能是解析cmdline并运行
int builtin_cmd(char **argv)：解析和执行bulidin命令，包括 quit, fg, bg, and jobs
void do_bgfg(char **argv) 执行bg和fg命令
void waitfg(pid_t pid)：实现阻塞等待前台程序运行结束
void sigchld_handler(int sig)：SIGCHID信号处理函数
void sigint_handler(int sig)：信号处理函数，响应 SIGINT (ctrl-c) 信号
void sigtstp_handler(int sig)：信号处理函数，响应 SIGTSTP (ctrl-z) 信号

辅助函数

可用辅助函数：

  • ​​int parseline(const char *cmdline,char **argv)​​：获取参数列表，返回是否为后台运行命令
  • ​​void clearjob(struct job_t *job)​​：清除​​job​​结构体。
  • ​​void initjobs(struct job_t *jobs)​​：初始化​​jobs​​链表。
  • ​​void maxjid(struct job_t *jobs)​​：返回​​jobs​​链表中最大的​​jid​​号。
  • ​​int addjob(struct job_t *jobs,pid_t pid,int state,char *cmdline)​​：在​​jobs​​链表中添加​​job​​
  • ​​int deletejob(struct job_t *jobs,pid_t pid)​​：在​​jobs​​链表中删除​​pid​​的​​job​​。
  • ​​pid_t fgpid(struct job_t *jobs)​​：返回当前前台运行​​job​​的​​pid​​号。
  • ​​struct job_t *getjobpid(struct job_t *jobs,pid_t pid)​​：返回​​pid​​号的​​job​​。
  • ​​struct job_t *getjobjid(struct job_t *jobs,int jid)​​：返回​​jid​​号的​​job​​。
  • ​​int pid2jid(pid_t pid)​​：将​​pid​​号转化为​​jid​​。
  • ​​void listjobs(struct job_t *jobs)​​：打印​​jobs​​。
  • ​​void sigquit_handler(int sig)​​：处理​​SIGQUIT​​信号。

简介

shell是交互式的命令行解释器，打印提示符并在stdin上等待输入命令，并按照命令行的内容执行。命令行是ASCII单词组成的命令和参数序列。若首个单词是内置命令，shell会立即在当前进程中执行。否则是可执行文件路径，shell派生出子进程，然后在该子进程的上下文中加载和运行程序。解释单个命令行而创建的子进程叫作业，通常由Unix管道连接的多个子进程组成。若命令行以&号“&”结束，则作业将在后台运行且不会等待作业结束。否则作业将在前台运行且等待作业终止。故在任何时间点最多仅一个作业在前台运行。但可在后台运行任意数量的作业。

例如：​​tsh> /bin/ls -l -d​​

在前台运行程序，程序的入口是：​​int main(int argc,char *argv[])​​

则argc==3，argv[0] == ‘‘/bin/ls’’，argv[1]== ‘‘-l’’,argv[2]== ‘‘-d’’。若在命令行后加上&，则在后台运行ls程序。shell支持作业控制，允许用户在后台和前台移动作业，并更改作业中进程的状态（运行、停止或终止）。输入ctrl-c会向前台作业中的每个进程发送SIGINT信号，默认操作是终止进程。类似地，键入ctrl-z将向前台作业中的每个进程发送SIGTSTP信号，默认操作是将进程置于停止状态，直到收到SIGCONT信号将其唤醒。当然shell也提供内置命令支持作业控制：

  • jobs：列出运行和终止的后台作业
  • bg <job>：将终止的后台作业改为运行
  • fg <job>：将终止或运行的后台作业改为前台运行
  • kill <job>：发送特定信号给特定进程和进程组，默认动作是终止进程
  • quit：终止shell

有三点值得注意：

  • tsh不支持管道和I/O重定向
  • 每个作业要么被process ID识别，要么被job ID识别，jid应该在命令行中用前缀“%”表示，“%5”表示jid 5，5表示PID 5
  • shell因该回收所有僵尸进程，若任何一个作业因为接收到它没有捕捉到的信号而终止，那么tsh应该识别该事件，并打印PID和错误描述消息

提示

  • 仔细阅读CSAPP第八章的异常控制流和lab的writeup
  • ​​make testn​​测试shell执行第n组测试数据的输出，​​make rtestn​​打印shell预期输出，​​tshref.out​​包含shell所有预期输出结果，先看文件输出，了解命令格式再编码，修改​​makefile​​文件中​​CFLAGS​​字段，加​​-g​​参数并去掉​​-O2​​参数
  • ​​waitpid​​, ​​kill​​, ​​fork​​,​​execve​​, ​​setpgid​​, ​​sigprocmask​​ 很常用，可通过命令手册查看使用细节，​​WUNTRACED​​和​​WNOHANG​​选项对​​waitpid​​也很有用
  • 实现信息处理函数，确保发送​​SIGINT​​和​​SIGTSTP​​信号给整个前台进程组，用​​-pid​​代替​​pid​​作为​​kill​​参数
  • 建议在​​waitfg​​的循环中用​​sleep​​函数，在​​sigchld_handler​​中对​​waitpid​​只调用一次
  • ​​eval​​中进程在​​fork​​之前用​​sigprocmask​​阻塞​​SIGCHLD​​信号，之后在解除信号阻塞，之后在调用​​addjob​​添加孩子到作业列表用​​sigprocmask​​阻塞信号，因为子继承继承父进程的阻塞集合，所以子程序必须确保在执行新进程前解除阻塞​​SIGCHLD​​信号。父进程需以这种方式阻塞​​SIGCHLD​​信号，避免在父进程调用​​addjob​​之前，​​SIGCHLD​​处理器获取子进程(从而从任务列表中删除)的竞争状态。
  • 不要直接调用常用命令，而应输入完整路径，如​​/bin/ls​​
  • 当在标准Unix shell运行tsh时，tsh运行在前台进程组中。若tsh随后创建子进程，默认情况下，该子进程也是前台进程组的成员。因为按下ctrl-c会向前台组中的每个进程发送SIGINT信号，按下ctrl-c会向tsh及Unix shell创建的每个子进程，显然不正确。应该在​​fork​​后，但在​​execve​​前，子进程调用​​setpgid(0,0)​​，把子进程放到新进程组中，该进程组ID与子进程的PID相同。确保前台进程组中只有一个进程，即tsh进程。当按下ctrl-c时，tsh应捕获生成的SIGINT，然后将其转发给包含前台作业的进程组。

实验前环境配置

由于csapp都是运行在32位系统，即使安装32位系统所需的库，仍然无法运行tsh，在网上找到有人配置好的csapp的docker镜像，因此直接使用docker，环境配置如下：

  1. 安装docker，并配置加速
  2. 安装vscode和ssh插件
  3. 命令行中运行​​systemctl start docker​​启动docker和​​docker run --privileged -d -p 1221:22 --name shell yansongsongsong/csapp:shelllab​​shell lab的实验环境
  4. 通过ssh输入密码登录实验环境

实验

在vscode中打开shlab-handout文件夹，并打开tsh.c文件，可以看到在​​main​​​函数中调用​​eval​​​函数，而在书P525或20-ecf-sigs的P19可找到​​eval​​函数的整体代码框架：

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;
}

尽管ppt上说有bug，暂时先不管，先搞好整体框架，完成简单的函数，到后面再考虑。另外值得一提的是这里将​​fork​​​和​​execve​​​都进行封装以处理错误情况。运行​​make rtest01​​​和​​make test01​​​可以看到输出一样，已经达到要求。同样操作，可以看到​​test02​​​未按照预期退出tsh，分析知需要实现​​builtin_cmd​​​函数。同样在书上P525能找到基础代码，只需加上​​jobs​​​、​​fg​​​、​​bg​​3种情况即可。代码如下：

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 */
}

这样就过了​​test02​​​和​​test03​​​，经过比较​​test04​​​和​​rtest04​​的输出，确定只需修改输出格式即可：

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

接着发现​​test05​​​是执行内部命令：​​jobs​​​，打印​​job list​​​，比对​​rtest05​​​发现没有打印出​​job​​​，参考上面的提示第6条，知应同步避免父子竞争，具体来说：父进程在​​fork​​​前屏蔽信号，子进程在​​execve​​​前还原信号，因为子进程会继承原来的屏蔽信号。同时前台​​job​​​需要调用​​waitfg​​​进行等待。如果不阻塞会出现子进程先结束从​​jobs​​​中删除，然后再执行到主进程​​addjob​​的竞争问题。在书上P542和PPT P57页都有对应的参考代码：

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);
}

加上图中对应代码，同时若子进程结束，需要delete job，在​​sigchld_handler​​中加上非阻塞循环等待子进程的代码：

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上面被调用，而上面回调用waitpid，因此这里不用调用只需循环等待即可
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，否则test05中运行到此处，前端进程执行jobs会阻塞直到所有子进程都被回收，即两个后端进程都执行并delete才会离开，则jobs命令什么也没有打印*/
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;
}

如果是前台命令，则调用​​waitfg​​​循环等待，在注释中看到最好不要用​​waitpid(pid,NULL,0)​​​，其次根据上面的提示，不要同时在​​sigchld_handler​​​和​​waitfg​​​函数中使用​​waitpid​​，因为在同一个程序的两个地方都回收僵死进程，虽然也行，但容易让人迷惑：

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

这样就完成​​test05​​​，接下来​​test06​​​和​​test07​​​、​​test08​​​就是实现​​SIGINT​​​和​​SIGSTOP​​​信号处理函数，注意前面提示的第4条用​​-pid​​​作为kill的参数，同时最后一条在​​fork​​​后​​execve​​​前子进程应调用​​setpgid(0,0)​​​，否则会报错​​No such process​​​，注意​​sigint_handler​​​和​​sigtstp_handler​​​只需调用​​kill​​​即可，将输出留到​​sigchld_handler​​​中，这样就需修改前面的​​sigchld_handler​​以处理不同子进程退出状态：

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，否则test05中运行到此处，前端进程执行jobs会阻塞直到所有子进程都被回收，即两个后端进程都执行并delete才会离开，则jobs命令什么也没有打印*/
while((pid = waitpid(-1,&status,WNOHANG | WUNTRACED))>0){
// WNOHANG | WUNTRACED 是立即返回
// 用WIFEXITED(status)，WIFSIGNALED(status)，WIFSTOPPED(status)等来补获终止或者
// 被停止的子进程的退出状态。
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))  // 信号退出 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 只修改状态就行
{
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;  // 恢复
return;
}

这样就完成​​test06​​​和​​test07​​​、​​test08​​​。接下来​​test09​​​和​​test10​​​是测试​​fg​​​和​​bg​​​内置命令，先解析命令通过​​getjobjid​​​或​​getjobpid​​​获取​​job​​​，再分情况对​​fg​​​和​​bg​​命令做不同处理，输入%num 代表任务id，num代表进程id，分情况讨论即可，但要注意各种异常情况：

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;
}

这样就过了​​test09​​​和​​test10​​​。接下来​​test11​​​ 和​​test12​​​ 、​​test13​​​分别测试​​Forward SIGINT​​​、​​Forward SIGTSTP​​​、​​Restart stopped process​​​都能正常通过，若没通过，因该是前面某些测试有问题，解决后即可。​​test14​​​是测试​​JID​​​或​​PID​​​的错误输入的情况，较容易通过。​​test15​​​将前面所有测试情况放一起，也顺利通过，而​​test16​​​是测试​​tsh​​​能否处理不是来自终端而是来自其他进程的​​SIGSTP​​​和​​SIGINT​​信号，顺利通过。

总结

最终代码见下，该实验主要涉及加载、进程控制、信号等基础但很重要的知识，涉及到异常控制流、进程、系统调用、信号处理函数与非本地跳转等并发编程的知识。并发的同步问题是关键，利用信号屏蔽与还原就能解决。此外阅读 man 手册了解系统接口使用细节对完成实验很有帮助。


/*
* 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，it call waitpid，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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