msh.c

/* 
 * msh - A mini 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>
#include "util.h"
#include "jobs.h"


/* Global variables */
int verbose = 0;            /* if true, print additional output */

extern char **environ;      /* defined in libc */
static char prompt[] = "msh> ";    /* command line prompt (DO NOT CHANGE) */
static 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 */
void usage(void);
void sigquit_handler(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.  
 * some codes are copied from H&O pg. 735,757
*/
 //#Jishen driving now
void eval(char *cmdline) 
{
    char *argv[MAXARGS];
    char buf[MAXLINE];
    int bg;
    pid_t pid;
    sigset_t mask;

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

    if(!builtin_cmd(argv)){
        //block SIGCHLD,SGSTP to avoid race condition.
        // addjob will execute before deletejob
        sigemptyset(&mask);
        sigaddset(&mask, SIGCHLD);
        sigaddset(&mask, SIGTSTP);
        sigprocmask(SIG_BLOCK, &mask, NULL); // Block SIGCHLD
        // child process
        if(((pid = fork()) == 0)){
            sigprocmask(SIG_UNBLOCK, &mask,NULL); // Unblock SIGCHLD
            setpgid(0,0);

            if(execve(argv[0], argv, environ) < 0){
                printf("%s: Command not found.\n", argv[0]);
                exit(0);
            }
        }        
        else{
            //parent process in foreground
            if(!bg){
                addjob(jobs,pid,FG,cmdline);
                sigprocmask(SIG_UNBLOCK, &mask, NULL);
                waitfg(pid);
            }
            //process in background
            else{
                addjob(jobs,pid,BG,cmdline);
                sigprocmask(SIG_UNBLOCK,&mask,NULL);
                printf("[%d] (%d) %s", pid2jid(jobs, pid), pid, cmdline); 
            }            
        }

    }
    return;
}
//#end of Jishen driving, Terry driving now 

/* 
 * builtin_cmd - If the user has typed a built-in command then execute
 *    it immediately.  
 * Return 1 if a builtin command was executed; return 0
 * if the argument passed in is *not* a builtin command.
 */
int builtin_cmd(char **argv) 
{
    if (!strcmp(argv[0], "quit")) /* quit command */
        exit(0);
    if (!strcmp(argv[0], "bg")){  /* background command */
        do_bgfg(argv);
        return 1;
    }  
    if (!strcmp(argv[0], "fg")){  /* foreground command */
        do_bgfg(argv);
        return 1;
    }  
    if (!strcmp(argv[0], "jobs")){ /* quit command */
        listjobs(jobs);
        return 1;
    }
    if (!strcmp(argv[0], "&"))   /* ignore singleton */
        return 1; 

    return 0;     /* not a builtin command */
}
//#end of Terry driving
/* 
 * do_bgfg - Execute the builtin bg and fg commands
 */

 //#Terry and Jishen drove here
void do_bgfg(char **argv) 
{   
    struct job_t *get_job;

    if(argv[1]!=NULL){
        if(atoi(argv[1])){
            int pid = atoi(argv[1]);
            get_job = getjobpid(jobs, pid);
            if (get_job == NULL) {
                printf("(%d): No such process \n", pid);
                return;            
            }            
        }
        //with %, get job id 
        else if (argv[1][0] == '%') {
            int jid = atoi(&argv[1][1]);
            get_job = getjobjid(jobs, jid); 
                if (getjobjid(jobs, jid) == NULL) {
                    printf("%%%d: No such job\n", jid);
                    return;
                }           
        } 
        //wrong input
        else{
            printf("%s: argument must be a PID or %%jobid\n", argv[0]);
            return;           
        }
        // background job
        if (!strcmp(argv[0], "bg")){
            if ((*get_job).state == ST){
                (*get_job).state = BG;
                kill((*get_job).pid, SIGCONT);
            }
            printf("[%d] (%d) %s", (*get_job).jid, (*get_job).pid, (*get_job).cmdline);
        } 
        // foreground job
        else if (!strcmp(argv[0], "fg")) {
            if ((*get_job).state == ST ) {
                (*get_job).state = FG;
                kill((*get_job).pid, SIGCONT);
                waitfg((*get_job).pid);
            }
            else if((*get_job).state == BG){
                (*get_job).state = FG;
                kill((*get_job).pid, SIGCONT);
                waitfg((*get_job).pid);                
            }
        }

    }
    else{
        printf("%s command requires PID or %%jobid argument\n", argv[0]);        
    }

    return;
}

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

    return;
}
//#End of Terry 
/*****************
 * 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.  
 *     Some codes are borrowed from B&O pg. 727
 */
  //#Jishen drove here
void sigchld_handler(int sig) 
{
    int status;
    pid_t pid;
    // Parent reaps children in no particular order
    while((pid = waitpid(-1, &status, WNOHANG|WUNTRACED)) > 0){
        //terminated normally
        if(WIFEXITED(status)){
            //printf("child %d terminated normally with exit status=%d\n",pid,WEXITSTATUS(status));
            deletejob(jobs,pid);
        }
        //terminated by SIGINT
        else if(WIFSIGNALED(status)){
            printf("Job [%d] (%d) terminated by signal 2\n", pid2jid(jobs, pid), pid);
            deletejob(jobs,pid);
        }
        //stoped by SIGTSTP
        else if(WIFSTOPPED(status)){
            printf("Job [%d] (%d) stopped by signal 20\n", pid2jid(jobs, pid), pid);
            (*getjobpid(jobs,pid)).state = ST;
        }
    }

    return;
}
//#End of Jishen driving
/* 
 * 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.  
 */
//#Terry driving now
void sigint_handler(int sig) 
{
    kill(-fgpid(jobs),SIGINT);
    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) 
{
    kill(-fgpid(jobs), SIGTSTP);
    return;
}
//# end of Terry driving

/*********************
 * End signal handlers
 *********************/



/***********************
 * 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);
}

/*
 * sigquit_handler - The driver program can gracefully terminate the
 *    child shell by sending it a SIGQUIT signal.
 */
void sigquit_handler(int sig) 
{
    ssize_t bytes;
    const int STDOUT = 1;
    bytes = write(STDOUT, "Terminating after receipt of SIGQUIT signal\n", 45);
    if(bytes != 45)
       exit(-999);
    exit(1);
}