CSAPP Lab：Shell Lab——理解进程控制的秘密

/* 
 * 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];
    char buf[MAXLINE];
    int isBg;
    pid_t pid;
    sigset_t mask;

    strcpy(buf,cmdline);
    isBg=parseline(buf,argv);
    if(argv[0]==NULL){
        return;
    }

    if(!builtin_cmd(argv)){
    //init mask
    sigemptyset(&mask);
    sigaddset(&mask,SIGCHLD);
    sigprocmask(SIG_BLOCK,&mask,NULL); //block SIGCHLD

        if((pid=fork())==0){
        sigprocmask(SIG_UNBLOCK,NULL); //unblock SIGCHLD
            if(execve(argv[0],argv,environ)<0){
                printf("%s:Command not found.n",argv[0]);
                exit(0);
            }
        
        //set own pid as group pid
        setpgid(0,0);
        }

        if(!isBg){
            addjob(jobs,pid,FG,cmdline);
            waitfg(pid);

        }
    else{
            addjob(jobs,BG,cmdline);
        printf("%d %s",cmdline);
    }
        sigprocmask(SIG_UNBLOCK,NULL); //unblock SIGCHLD
    }
    

    return;
}

/* 
 * 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")||!strcmp(argv[0],"q")){
        exit(0);
    }
    if(!strcmp(argv[0],"jobs")){
        listjobs(jobs);
    return 1;
    }
    if(!strcmp(argv[0],"bg")||!strcmp(argv[0],"fg")){
    do_bgfg(argv);
    return 1;
    }
    return 0; 
}

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

    if(id==NULL){
        printf("%s command requireds pid or %%jobid argumentn",argv[0]);
        return;
    }

    //process by jobid
    if(id[0]==‘%‘)
    {
        int jid = atoi(&id[1]);
        job=getjobjid(jobs,jid);
        if(job==NULL)
        {
            printf("%s:No such jobn",id);
            return;
        }
    }
    //process by pid
    else if(isdigit(id[0])){
    int pid = atoi(&id[1]);
    job = getjobpid(jobs,pid);
        if(job==NULL)
        {
            printf("%s:No such jobn",id);
            return;
        }    
    }
    else{
        printf("%s: argument must be a PID or %%jobidn",argv[0]);
        return;
    }
    //send SIGCONT to restart
    kill(-(job->pid),SIGCONT);
    //set job status
    if(!strcmp(argv[0],"bg")){
        job->state = BG;
        printf("[%d] (%d) %s",job->jid,job->pid,job->cmdline);
    }else{
        job->state = FG;
        waitfg(job->pid);
    }


    return;
}

/* 
 * waitfg - Block until process pid is no longer the foreground process
 */
void waitfg(pid_t pid)
{
    while(pid == fgpid(jobs)){
        sleep(0);
    }
}

void sigchld_handler(int sig) 
{
    pid_t pid;
    int status;
    while((pid = waitpid(-1,&status,WNOHANG|WUNTRACED))>0){
        if(WIFEXITED(status)){
            deletejob(jobs,pid);
        }
        if(WIFSIGNALED(status)){
            deletejob(jobs,pid);
        }
        if(WIFSTOPPED(status)){
            struct job_t *job = getjobpid(jobs,pid);
            if(job !=NULL ){
        job->state = ST;
        }
        }
    }
    if(errno != ECHILD)
        unix_error("waitpid error");

    return;
}

void sigint_handler(int sig) 
{
    pid_t pid = fgpid(jobs);
    if(pid!=0){
        kill(-pid,sig);
    }
    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 = fgpid(jobs);

    if(pid!=0 ){
        struct job_t *job = getjobpid(jobs,pid);
        if(job->state == ST){
            return;
        }else{
            Kill(-pid,SIGTSTP);
        }
    }
    return;
}