试验目标
shell lab 次要目标是为了相熟过程管制和信号。具体来说须要比对 16 个 test 和 rtest 文件的输入，实现五个函数：
void eval(char *cmdline)：剖析命令，并派生子过程执行 次要性能是解析 cmdline 并运行
int builtin_cmd(char **argv)：解析和执行 bulidin 命令，包含 quit, fg, bg, and jobs
void do_bgfg(char **argv) 执行 bg 和 fg 命令
void waitfg(pid_t pid)：实现阻塞期待前台程序运行完结
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，返回是否为后盾运行命令void clearjob(struct job_t *job)：革除job构造体。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链表中增加jobint 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)：返回以后前台运行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)：解决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 上期待输出命令，并依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 会立刻在以后过程中执行。否则是可执行文件门路，shell 派生出子过程，而后在该子过程的上下文中加载和运行程序 。解释单个命令行而创立的子过程叫 作业 ，通常由 Unix 管道连贯的多个子过程组成。 若命令行以 & 号“&”完结，则作业将在后盾运行且不会期待作业完结。否则作业将在前台运行且期待作业终止。故在任何工夫点最多仅一个作业在前台运行。但可在后盾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 &，则在后盾运行 ls 程序。shell 反对作业控制，容许用户在后盾和前台挪动作业，并更改作业中过程的状态（运行、进行或终止）。输出 ctrl- c 会向前台作业中的每个过程发送 SIGINT 信号，默认操作是终止过程。相似地，键入 ctrl- z 将向前台作业中的每个过程发送 SIGTSTP 信号，默认操作是将过程置于进行状态，直到收到 SIGCONT 信号将其唤醒。当然 shell 也提供内置命令反对作业控制：
- 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过程和过程组，默认动作是终止过程
- quit：终止 shell
有三点值得注意：
- tsh 不反对管道和 I / O 重定向
- 每个作业要么被 process ID 辨认，要么被 job ID 辨认，jid 因该在命令行中用前缀“%”示意，“%5”示意 jid 5，5 示意 PID 5
- shell 因该回收所有僵尸过程，若任何一个作业因为接管到它没有捕捉到的信号而终止，那么 tsh 应该辨认该事件，并打印 PID 和谬误形容音讯
提醒
- 仔细阅读 CSAPP 第八章的异样控制流和 lab 的 writeup
make testn测试 shell 执行第 n 组测试数据的输入，make rtestn打印 shell 预期输入，tshref.out蕴含 shell 所有预期输入后果，先看文件输入，理解命令格局再编码，批改makefile文件中CFLAGS字段，加-g参数并去掉-O2参数waitpid,kill,fork,execve,setpgid,sigprocmask很罕用，可通过命令手册查看应用细节，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信号给整个前台过程组，用-pid代替pid作为kill参数 - 倡议在
waitfg的循环中用sleep函数，在sigchld_handler中对waitpid只调用一次 eval中过程在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增加孩子到作业列表用sigprocmask阻塞信号，因为子继承继承父过程的阻塞汇合，所以子程序必须确保在执行新过程前解除阻塞SIGCHLD信号。父过程需以这种形式阻塞SIGCHLD信号，防止在父过程调用addjob之前，SIGCHLD处理器获取子过程 (从而从工作列表中删除) 的竞争状态。- 不要间接调用常用命令，而应输出残缺门路，如
/bin/ls - 当在规范 Unix shell 运行 tsh 时，tsh 运行在前台过程组中。若 tsh 随后创立子过程，默认状况下，该子过程也是前台过程组的成员。因为按下 ctrl- c 会向前台组中的每个过程发送 SIGINT 信号，按下 ctrl- c 会向 tsh 及 Unix shell 创立的每个子过程，显然不正确。应该在
fork后，但在execve前，子过程调用setpgid(0,0)，把子过程放到新过程组中，该过程组 ID 与子过程的 PID 雷同。确保前台过程组中只有一个过程，即 tsh 过程。当按下 ctrl- c 时，tsh 应捕捉生成的 SIGINT，而后将其转发给蕴含前台作业的过程组。
试验前环境配置
因为 csapp 都是运行在 32 位零碎，即便装置 32 位零碎所需的库，依然无奈运行 tsh，在网上找到有人配置好的 csapp 的 docker 镜像，因而间接应用 docker，环境配置如下：
- 装置 docker，并配置减速
- 装置 vscode 和 ssh 插件
- 命令行中运行
systemctl start docker启动 docker 和docker run --privileged -d -p 1221:22 --name shell yansongsongsong/csapp:shelllabshell lab 的试验环境 - 通过 ssh 输出明码登录试验环境
试验
在 vscode 中关上 shlab-handout 文件夹，并关上 tsh.c 文件，能够看到在 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;
}只管 ppt 上说有 bug，临时先不论，先搞好整体框架，实现简略的函数，到前面在思考。另外值得一提的是这里将 fork 和execve都进行封装以处理错误状况。
运行 make rtest01 和make test01能够看到输入一样，曾经达到要求。同样操作，能够看到 test02 未依照预期退出 tsh，剖析知须要实现 builtin_cmd 函数。同样在书上 P525 能找到根底代码，只需加上jobs、fg、bg 3 种状况即可。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，通过比拟 test04 和rtest04的输入，确定只需批改输入格局即可：
printf("[%d] (%d) %s", pid2jid(pid),pid, cmdline);接着发现 test05 是执行外部命令：jobs，打印 job list，比对rtest05 发现没有打印出 job，参考下面的提醒第 6 条，知应同步防止父子竞争，具体来说：父过程在fork 前屏蔽信号，子过程在 execve 前还原信号，因为子过程回继承原来的屏蔽信号。同时前台 job 须要调用 waitfg 进行期待。如果不阻塞会呈现子过程先完结从 jobs 中删除，而后再执行到主过程 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，同时若子过程完结，须要 delete job，在 sigchld_handler 中加上非阻塞循环期待子过程的代码：
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) {
// 因为 sigchld_handler 下面被调用，而下面回调用 waitpid，因而这里不必调用只需循环期待即可
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，前端过程执行 jobs 会阻塞直到所有子过程都被回收，即两个后端过程都执行并 delete 才会来到，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 循环期待，在正文中看到最好不要用 waitpid(pid,NULL,0)，其次依据下面的提醒，不要同时在sigchld_handler 和waitfg函数中应用waitpid，因为在同一个程序的两个中央都回收僵死过程，尽管也行，但容易让人蛊惑：
void waitfg(pid_t pid)
{while(fgpid(jobs))
usleep(1000);// 一秒
return;
}这样就实现 test05，接下来test06 和test07、test08就是实现 SIGINT 和SIGSTOP信号处理函数，留神后面提醒的第 4 条用 -pid 作为 kill 的参数，同时最初一条在 fork 后execve前子过程应调用 setpgid(0,0)，否则回报错No such process，留神sigint_handler 和sigtstp_handler只需调用 kill 即可，将输入留到 sigchld_handler 中，这样就需批改后面的 sigchld_handler 以解决不同子过程退出状态：
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，前端过程执行 jobs 会阻塞直到所有子过程都被回收，即两个后端过程都执行并 delete 才会来到，则 jobs 命令什么也没有打印 */
while((pid = waitpid(-1,&status,WNOHANG | WUNTRACED))>0){
// WNOHANG | WUNTRACED 是立刻返回
// 用 WIFEXITED(status)，WIFSIGNALED(status)，WIFSTOPPED(status)等来补获终止或者
// 被进行的子过程的退出状态。if (WIFEXITED(status)) // 失常退出 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 // 进行 只批改状态就行
{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; // 复原
return;
}这样就实现 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，再分状况对fg 和bg命令做不同解决，输出 %num 代表工作 id，num 代表过程 id，分状况探讨即可，但要留神各种异常情况：
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 别离测试 Forward SIGINT 、Forward SIGTSTP、Restart stopped process 都能失常通过，若每通过，因该是后面某些测试有问题，解决后即可。test14是测试 JID 或PID的谬误输出的状况，较容易通过。test15将后面所有测试状况放一起，也顺利通过，而 test16 是测试 tsh 是否解决不是来自终端而是来自其余过程的 SIGSTP 和SIGINT信号，顺利通过。
总结
最终代码见下，该试验次要波及加载、过程管制、信号等根底但很重要的常识，波及到异样控制流、过程、零碎调用、信号处理函数与非本地跳转等并发编程的常识。并发的同步问题是要害，利用信号屏蔽与还原就能解决。此外浏览 man 手册理解零碎接口应用细节对实现试验很有帮忙。
/*
* 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;
}本文由博客一文多发平台 OpenWrite 公布！