CSAPP SHLAB

CSAPP SHLAB

这个lab总体来说不难，书上都有讲到，而且要注意的地方提示里都有写。不过还是花了挺多时间的。

---

遇到的问题

子进程停止后，父进程会在waitpid(pid,&status,WUNTRACED)中得到该子进程pid。但是再次使用waitpid(-1,&status,WNOHANG|WUNTRACED)时会忽视该子进程。
本想在waitfg中使用waitpid来挂起父进程等待，在sigchld_handler中使用waitpid(-1,&status,WNOHANG|WUNTRACED)处理子进程的。由于这个问题只好在waitfg中用pause函数来等待子进程了。（提示中说使用sleep函数）

具体代码

/* 
 * tsh - A tiny shell program with job control
 * 
 * 
 */
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

/* 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 */


/* 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);

pid_t Fork(void);
void Kill(pid_t pid, int sig);

/*
 * 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];
    pid_t pid;
    sigset_t mask;
    int bg;

    bg = parseline(cmdline, argv);//empty line return 1
    if(argv[0] && !builtin_cmd(argv)){//not builtin cmd
        sigemptyset(&mask);
        sigaddset(&mask, SIGCHLD);
        sigprocmask(SIG_BLOCK, &mask, NULL);//block SIGCHLD
        if((pid = Fork())==0){
            sigprocmask(SIG_UNBLOCK, &mask, NULL);//unblock
            setpgid(0, 0);
            if(execve(argv[0], argv, environ) < 0){
                printf("%s: Command not found\n", argv[0]);
                exit(1);//in son process so can't return
            }
        }else{
            if(!bg){
                if(!addjob(jobs, pid, FG, cmdline)){
                    app_error("create job failed");
                };

                sigprocmask(SIG_UNBLOCK, &mask, NULL);//unblock
                waitfg(pid);
            }else{
                if(!addjob(jobs, pid, BG, cmdline)){
                    app_error("create job failed");
                };

                sigprocmask(SIG_UNBLOCK, &mask, NULL);//unblock
                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")){
        exit(0);
    }

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

/* 
 * do_bgfg - Execute the builtin bg and fg commands
 */
void do_bgfg(char **argv) 
{
    int bg = 0;
    int jid;
    pid_t pid;
    struct job_t *job;
    char *arg = argv[1];

    if(!arg || arg[0]=='&'){
        printf("%s command requires PID or %%jobid argument\n", argv[0]);
        return;
    }
    if(arg[0]!='%' && (arg[0]<'0' || arg[0]>'9')){
        printf("%s: argument must be a PID or %%jobid\n", argv[0]);
        return;
    }

    //get job
    if(arg[0]=='%'){
        jid = atoi(++arg);
        if(!jid){
            printf("%s: No such job\n", argv[1]);
            return;
        }
        job = getjobjid(jobs, jid);
        if(!job){
            printf("%s: No such job\n", argv[1]);
            return;
        }
        pid = job->pid;
    }else{
        pid = atoi(arg);
        job = getjobpid(jobs, pid);
        if(!job){
            printf("(%d): No such process\n", pid);
            return;
        }
    }

    //do bg or fg
    if(!strcmp(argv[0],"bg")){
        bg = 1;
    }
    if(bg){
        Kill(-pid, SIGCONT);
        job->state = BG;  
        printf("[%d] (%d) %s", job->jid, job->pid, job->cmdline);
    }else{
        Kill(-pid, SIGCONT);
        job->state = FG;
        waitfg(pid);
    }
    return;
}

/* 
 * waitfg - Block until process pid is no longer the foreground process
 */
void waitfg(pid_t pid)
{   
    struct job_t *job;
    job = getjobpid(jobs, pid);

    while(1){
        pause();
        if((job->pid == 0 && job->state == UNDEF) || 
            (job->pid == pid && job->state == ST)){
            if(verbose){
                printf("waitfg: Process (%d) no longer the fg process\n", pid);
            }
            break;
        }
    }
    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) 
{
    pid_t pid;
    struct job_t *job;
    int jid;
    int status;

    if(verbose){
        printf("sigchld_handler: entering\n");
    }

    while((pid = waitpid(-1, &status, WUNTRACED | WNOHANG)) > 0){
        job = getjobpid(jobs, pid);
        if(!job){
            app_error("can't find the job");
        }
        jid = job->jid;

        if(WIFEXITED(status)){
            if(deletejob(jobs, pid)){
                if(verbose){
                    printf("sigchld_handler: Job [%d] (%d) deleted\n", jid, pid);
                }
            }else{
                app_error("can't delete job");
            }

            if(verbose){
                printf("sigchld_handler: Job [%d] (%d) terminates OK (status %d)\n", jid, pid, WEXITSTATUS(status));
            }
        }

        if(WIFSIGNALED(status)){
            if(deletejob(jobs, pid)){
                if(verbose){
                    printf("sigchld_handler: Job [%d] (%d) deleted\n", jid, pid);
                }
            }else{
                app_error("can't delete job");
            }

            printf("Job [%d] (%d) terminated by signal %d\n", jid, pid, WTERMSIG(status));
        }

        if(WIFSTOPPED(status)){
            job->state = ST;
            printf("Job [%d] (%d) stopped by signal %d\n", jid, pid, WSTOPSIG(status));
        }
    }

    //waitpid返回值如果为0，说明waitpid没有出错，而可能是别的函数报错，比如pause
    if(pid < 0 && errno != ECHILD){ 
        unix_error("waitpid error");
    }

    if(verbose){
        printf("sigchld_handler: exiting\n");
    }
    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) 
{
    if(verbose){
        printf("sigint_handler: entering\n");
    }

    pid_t pid;
    pid = fgpid(jobs);
    if(pid){
        Kill(-pid, SIGINT);
        if(verbose){
            printf("sigint_handler: Job (%d) killed\n", pid);
        }
    }

    if(verbose){
        printf("sigint_handler: exiting\n");
    }
    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) 
{
    pid_t pid;
    if(verbose){
        printf("sigtstp_handler: entering\n");
    }

    pid = fgpid(jobs);
    if(pid){
        Kill(-pid, SIGTSTP);//状态统一在sigchld_handler中处理
        if(verbose){
            printf("sigint_handler: Job [%d] (%d) stopped\n", pid2jid(pid), pid);
        }
    }

    if(verbose){
        printf("sigtstp_handler: exiting\n");
    }
    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);/* return old 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);
}

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

void Kill(pid_t pid, int sig){
    if(kill(pid,sig) < 0){
        unix_error("Signal error");
    }
}