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《深入理解计算机系统》CSAPP_TshLab

作者：互联网

TshLab

开始日期：22.1.20

操作系统：linux

调试工具：linux terminal

目录

Preknowledge

Functions

Attention

eval()

void eval(char *cmdline) {
    char *argv[MAXARGS];
    char buf[MAXLINE];
    int bg;   
    pid_t pid;
    sigset_t mask_all, mask_one, prev;
	
    sigfillset(&mask_all); //fill all sigs to mask
    sigemptyset(&mask_one);
    sigaddset(&mask_one, SIGCHLD); //mask_one has one sig: SIGCHLD
    //initjobs(jobs); already use in main(), recalled will empty new lists of jobs

    strcpy(buf, cmdline);
    bg = parseline(buf, argv); //return true, if it is background 
    if(argv[0] == NULL) //if not any cmd
        return;
    //exeluate buliltin_cmd, if not buliltin_cmd(filepath, ./exe and so on), shell will create a child process and run it
    if(!builtin_cmd(argv)) { 
    	sigprocmask(SIG_BLOCK, &mask_one, &prev); //block SIGCHLD to avoid race
        if((pid = fork()) == 0){ //create a child process
        	setpgid(0, 0); //or call setpgrp()
        	sigprocmask(SIG_SETMASK, &prev, NULL); //unblock SIGCHLD
            if(execve(argv[0], argv, environ) < 0) { //run it and if it can't run
                printf("%s: Command not found.\n", argv[0]);
                exit(0);
            }
        }
     	
     	//before add/delete job, we must block all sigs
     	sigprocmask(SIG_BLOCK, &mask_all, NULL);  /* Parent: block all sigs */   
     	
     	//background: 
    	if(bg) {
     		addjob(jobs, pid, BG, cmdline); // add job to jobs(list) in background
     		sigprocmask(SIG_SETMASK, &prev, NULL); /* Unblock all sig */
     		// get jid by pid
     		printf("[%d] (%d) %s", pid2jid(pid), pid, cmdline);      	
     	}
     	
     	//foreground: If the job is running in the foreground, wait for it to terminate and then return.
     	else { 
    		flag = 0; //job running in foreground
     		addjob(jobs, pid, FG, cmdline);
     		//Still block until process pid is no longer the foreground process
     		waitfg(pid);
     	}
   }
   return;
}

do_bgfg()

void do_bgfg(char **argv) 
{	
	if (argv[1] == NULL){
		printf("%s command requires PID or %%jobid argument\n", argv[0]);
		return;
	}
	
	//define argument, if argv[1] has value
	struct job_t *job_ptr = NULL;
	int isjob;
	int bg = 0;
	pid_t jid, pid;

	//printf error message
	if (sscanf(argv[1], "%d", &pid) > 0){
		isjob = 0;
		job_ptr = getjobpid(jobs, pid);
		//printf error if state of job is undefine or tan90°(non-being)
		//Note: (job_ptr == NULL) Before (job_ptr->state == UNDEF)
		if ((job_ptr == NULL) || (job_ptr->state == UNDEF)) {
			printf("(%d): No such process\n", pid);
			return;
		}	
	}
	else if (sscanf(argv[1], "%%%d", &jid) > 0){
		isjob = 1;
		job_ptr = getjobjid(jobs, jid);
		if ((job_ptr == NULL) || (job_ptr->state == UNDEF)) {
			printf("%%%d: No such job\n", jid);
			return;
		}	
	}
	else {
		printf("%s: argument must be a PID or %%jobid\n", argv[0]);
		return;
	}
	
	if(!strcmp(argv[0], "bg"))
		bg = 1;
	// bg command			
	if (bg){
		if(job_ptr->state == BG){
			printf("[%d] (%d) %s", jid, job_ptr->pid, job_ptr->cmdline);	
		}
		//restart
		if(job_ptr->state == ST){
			if (isjob)
				kill(-(job_ptr->pid), SIGCONT);
			else
				kill((job_ptr->pid), SIGCONT);
			job_ptr->state = BG;
			printf("[%d] (%d) %s", jid, job_ptr->pid, job_ptr->cmdline);
		}
	}
	//fg command
	else { 
			//block all sig, after return or terminated in fg
			sigset_t mask_all;
			sigfillset(&mask_all);
			sigprocmask(SIG_BLOCK, &mask_all, NULL);
			flag = 0; //job running in foreground
    
			//when "fg %1 "is typed a second time, will sents SIGCONT to restart job/process
			if (job_ptr -> state == ST){
				if (isjob)
					kill(-(job_ptr->pid), SIGCONT);
				else
					kill((job_ptr->pid), SIGCONT);
			}
			job_ptr->state = FG;
			waitfg(job_ptr->pid);
			return;
	}
	return;
}

waitfg()

void waitfg(pid_t pid)
{
	sigset_t empty;
	sigemptyset(&empty); //an empty set
	while (!flag) //flag == 0 => job running in foreground => !flag == 1
		sigsuspend(&empty); //suspend, we must wait job terminated in foreground explicitly 
	sigprocmask(SIG_SETMASK, &empty, NULL); /* Unblock all sig */	
	return;
}

builtin_cmd()

int builtin_cmd(char **argv) 
{
    if(!strcmp(argv[0], "quit")) // if equal, strcmp() return 0, so !strcmp() return 1
        exit(0);
    if(!strcmp(argv[0], "jobs")){
        listjobs(jobs);
        return 1;
    }
    if(!strcmp(argv[0], "fg") || !strcmp(argv[0], "bg")){
        do_bgfg(argv);
        return 1;
    }
    if(!strcmp(argv[0], "&")) // ignore alone '&'
        return 1;
    return 0;     /* not a builtin command */
}

sigchld_handler()

void sigchld_handler(int sig) 
{
        int olderrno = errno;
        int status;
        pid_t pid, fg_pid = fgpid(jobs); //Note: only one job in fg
	
        if ((pid = waitpid(-1, &status, WNOHANG | WUNTRACED)) > 0) { 
	    if(pid == fg_pid)
		flag = 1;
	    if (WIFEXITED(status)) //normally terminated (return/exit)
	    	deletejob(jobs, pid);
	    else if (WIFSIGNALED(status)){  //child terminated because SIGINT that was caught.
		printf("Job [%d] (%d) terminated by signal %d\n", pid2jid(pid), pid, WTERMSIG(status));
		deletejob(jobs, pid);
	    }
    	    else if (WIFSTOPPED(status)){
   	        struct job_t *job_ptr = getjobpid(jobs, pid);//getjobpid() return address of job
                job_ptr->state = ST; //stopped the job   			
		printf("Job [%d] (%d) stopped by signal %d\n", pid2jid(pid), pid, WSTOPSIG(status));
    	    }          
         }
    
        errno = olderrno;
        return;
}

sigint_handler()

void sigint_handler(int sig) 
{	
  int olderrno = errno;
  //get pid from jobs in 'fg'
  pid_t pgid = fgpid(jobs);  //process ground in fg: fg_pid == pgid == pid != 0
  
  //sent SIGINT to pgid in order to terminate the whole fg ground  
  if (pgid) {
      kill(-pgid, SIGINT); //or call killpg(-pgid, SIGINT)
  }
  errno = olderrno;
  return;
}

sigstp_handler()

void sigtstp_handler(int sig) 
{	
    int olderrno = errno;
    pid_t pgid = fgpid(jobs);  //process ground in fg: fg_pid == pgid == pid != 0
  
    //sent SIGTSTP to pgid in order to stopped the whole fg ground 
    if (pgid) {
	kill(-pgid, SIGTSTP); 
    }
    errno = olderrno;
    return;
}

Put all together

/* 
 * tsh - A tiny shell program with job control
 * 
 * <duile programme>
 */
#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 */
volatile  sig_atomic_t flag; /* equal 1 => jobs terminated or stopped in fg; equal 0 => jobs running in fg */

/* 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);

/*
 * 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];
    char buf[MAXLINE];
    int bg;   
    pid_t pid;
	sigset_t mask_all, mask_one, prev;
	
	sigfillset(&mask_all); //fill all sigs to mask
	sigemptyset(&mask_one);
	sigaddset(&mask_one, SIGCHLD); //mask_one has one sig: SIGCHLD
	//initjobs(jobs); already use in main(), recalled will empty new lists of jobs

    strcpy(buf, cmdline);
    bg = parseline(buf, argv); //return true, if it is background 
    if(argv[0] == NULL) //if not any cmd
        return;
    //exeluate buliltin_cmd, if not buliltin_cmd(filepath, ./exe and so on), shell will create a child process and run it
    if(!builtin_cmd(argv)) { 
    	sigprocmask(SIG_BLOCK, &mask_one, &prev); //block SIGCHLD to avoid race
        if((pid = fork()) == 0){ //create a child process
        	setpgid(0, 0); //or call setpgrp()
        	sigprocmask(SIG_SETMASK, &prev, NULL); //unblock SIGCHLD
            if(execve(argv[0], argv, environ) < 0) { //run it and if it can't run
                printf("%s: Command not found.\n", argv[0]);
                exit(0);
            }
        }
     	
     	//before add/delete job, we must block all sigs
     	sigprocmask(SIG_BLOCK, &mask_all, NULL);  /* Parent: block all sigs */   
     	
     	//background: 
    	if(bg) {
     		addjob(jobs, pid, BG, cmdline); // add job to jobs(list) in background
     		sigprocmask(SIG_SETMASK, &prev, NULL); /* Unblock all sig */
     		// get jid by pid
     		printf("[%d] (%d) %s", pid2jid(pid), pid, cmdline);      	
     	}
     	
     	//foreground: If the job is running in the foreground, wait for it to terminate and then return.
     	else { 
    		flag = 0; //job running in foreground
     		addjob(jobs, pid, FG, cmdline);
     		//Still block until process pid is no longer the foreground process
     		waitfg(pid);
     	}
   }
   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")) // if equal, strcmp() return 0, so !strcmp() return 1
        exit(0);
    if(!strcmp(argv[0], "jobs")){
        listjobs(jobs);
        return 1;
    }
    if(!strcmp(argv[0], "fg") || !strcmp(argv[0], "bg")){
        do_bgfg(argv);
        return 1;
    }
    if(!strcmp(argv[0], "&")) // ignore alone '&'
        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] == NULL){
		printf("%s command requires PID or %%jobid argument\n", argv[0]);
		return;
	}
	
	//define argument, if argv[1] has value
	struct job_t *job_ptr = NULL;
	int isjob;
	int bg = 0;
	pid_t jid, pid;

	//printf error message
	if (sscanf(argv[1], "%d", &pid) > 0){
		isjob = 0;
		job_ptr = getjobpid(jobs, pid);
		//printf error if state of job is undefine or tan90°(non-being)
		//Note: (job_ptr == NULL) Before (job_ptr->state == UNDEF)
		if ((job_ptr == NULL) || (job_ptr->state == UNDEF)) {
			printf("(%d): No such process\n", pid);
			return;
		}	
	}
	else if (sscanf(argv[1], "%%%d", &jid) > 0){
		isjob = 1;
		job_ptr = getjobjid(jobs, jid);
		if ((job_ptr == NULL) || (job_ptr->state == UNDEF)) {
			printf("%%%d: No such job\n", jid);
			return;
		}	
	}
	else {
		printf("%s: argument must be a PID or %%jobid\n", argv[0]);
		return;
	}
	
	if(!strcmp(argv[0], "bg"))
		bg = 1;
	// bg command			
	if (bg){
		if(job_ptr->state == BG){
			printf("[%d] (%d) %s", jid, job_ptr->pid, job_ptr->cmdline);	
		}
		//restart
		if(job_ptr->state == ST){
			if (isjob)
				kill(-(job_ptr->pid), SIGCONT);
			else
				kill((job_ptr->pid), SIGCONT);
			job_ptr->state = BG;
			printf("[%d] (%d) %s", jid, job_ptr->pid, job_ptr->cmdline);
		}
	}
	//fg command
	else { 
			//block all sig, after return or terminated in fg
			sigset_t mask_all;
			sigfillset(&mask_all);
			sigprocmask(SIG_BLOCK, &mask_all, NULL);
			flag = 0; //job running in foreground
    
			//when "fg %1 "is typed a second time, will sents SIGCONT to restart job/process
			if (job_ptr -> state == ST){
				if (isjob)
					kill(-(job_ptr->pid), SIGCONT);
				else
					kill((job_ptr->pid), SIGCONT);
			}
			job_ptr->state = FG;
			waitfg(job_ptr->pid);
			return;
	}
	return;
}
/* 
 * waitfg - Block until process pid is no longer the foreground process
 */
void waitfg(pid_t pid)
{
	sigset_t empty;
	sigemptyset(&empty); //an empty set
	while (!flag) //flag == 0 => job running in foreground => !flag == 1
		sigsuspend(&empty); //suspend, we must wait job terminated in foreground explicitly 
	sigprocmask(SIG_SETMASK, &empty, NULL); /* Unblock all sig */	
	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;
	int status;
	pid_t pid, fg_pid = fgpid(jobs); //Note: only one job in fg
	
  	if ((pid = waitpid(-1, &status, WNOHANG | WUNTRACED)) > 0) { 
		if(pid == fg_pid)
			flag = 1;
	    if (WIFEXITED(status)) //normally terminated (return/exit)
	    	deletejob(jobs, pid);
	    else if (WIFSIGNALED(status)){  //child terminated because SIGINT that was caught.
			printf("Job [%d] (%d) terminated by signal %d\n", pid2jid(pid), pid, WTERMSIG(status));
			deletejob(jobs, pid);
	    }
    	else if (WIFSTOPPED(status)){
   			struct job_t *job_ptr = getjobpid(jobs, pid);//getjobpid() return address of job
        	job_ptr->state = ST; //stopped the job   			
			printf("Job [%d] (%d) stopped by signal %d\n", pid2jid(pid), pid, WSTOPSIG(status));
    	}          
 	}
    
    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;
	//get pid from jobs in 'fg'
	pid_t pgid = fgpid(jobs);  //process ground in fg: fg_pid == pgid == pid != 0
  
	//sent SIGINT to pgid in order to terminate the whole fg ground  
	if (pgid) {
		kill(-pgid, SIGINT); //or call killpg(-pgid, SIGINT)
	}
  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 pgid = fgpid(jobs);  //process ground in fg: fg_pid == pgid == pid != 0
  
	//sent SIGTSTP to pgid in order to stopped the whole fg ground 
	if (pgid) {
		kill(-pgid, SIGTSTP); 
	}
  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);
}

trace15 & 16

Conclusion

标签：计算机系统,CSAPP,jobs,int,pid,argv,job,return,TshLab
来源： https://www.cnblogs.com/duile/p/15844194.html