jobs.c

操作系统源代码

	{
	int pid;
	int pgrp;

	TRACE(("forkshell(%%%d, 0x%x, %d) called\n", jp - jobtab, (int)n, mode));
	INTOFF;
	pid = fork();
	if (pid == -1) {
		TRACE(("Fork failed, errno=%d\n", errno));
		INTON;
		error("Cannot fork");
	}
	if (pid == 0) {
		struct job *p;
		int wasroot;
		int i;

		TRACE(("Child shell %d\n", getpid()));
		wasroot = rootshell;
		rootshell = 0;
		for (i = njobs, p = jobtab ; --i >= 0 ; p++)
			if (p->used)
				freejob(p);
		closescript();
		INTON;
		clear_traps();
#if JOBS
		jobctl = 0;		/* do job control only in root shell */
		if (wasroot && mode != FORK_NOJOB && jflag) {
			if (jp == NULL || jp->nprocs == 0)
				pgrp = getpid();
			else
				pgrp = jp->ps[0].pid;
			setpgrp(0, pgrp);
			if (mode == FORK_FG) {
				/*** this causes superfluous TIOCSPGRPS ***/
				if (ioctl(2, TIOCSPGRP, (char *)&pgrp) < 0)
					error("TIOCSPGRP failed, errno=%d\n", errno);
			}
			setsignal(SIGTSTP);
			setsignal(SIGTTOU);
		} else if (mode == FORK_BG) {
			ignoresig(SIGINT);
			ignoresig(SIGQUIT);
			if ((jp == NULL || jp->nprocs == 0)
			    && ! fd0_redirected_p ()) {
				close(0);
				if (open("/dev/null", O_RDONLY) != 0)
					error("Can't open /dev/null");
			}
		}
#else
		if (mode == FORK_BG) {
			ignoresig(SIGINT);
			ignoresig(SIGQUIT);
			if ((jp == NULL || jp->nprocs == 0)
			    && ! fd0_redirected_p ()) {
				close(0);
				if (open("/dev/null", O_RDONLY) != 0)
					error("Can't open /dev/null");
			}
		}
#endif
		if (wasroot && iflag) {
			setsignal(SIGINT);
			setsignal(SIGQUIT);
			setsignal(SIGTERM);
		}
		return pid;
	}
	if (rootshell && mode != FORK_NOJOB && jflag) {
		if (jp == NULL || jp->nprocs == 0)
			pgrp = pid;
		else
			pgrp = jp->ps[0].pid;
#if JOBS
		setpgrp(pid, pgrp);
#endif
	}
	if (mode == FORK_BG)
		backgndpid = pid;		/* set $! */
	if (jp) {
		struct procstat *ps = &jp->ps[jp->nprocs++];
		ps->pid = pid;
		ps->status = -1;
		ps->cmd = nullstr;
		if (iflag && rootshell && n)
			ps->cmd = commandtext(n);
	}
	INTON;
	TRACE(("In parent shell:  child = %d\n", pid));
	return pid;
}



/*
 * Wait for job to finish.
 *
 * Under job control we have the problem that while a child process is
 * running interrupts generated by the user are sent to the child but not
 * to the shell.  This means that an infinite loop started by an inter-
 * active user may be hard to kill.  With job control turned off, an
 * interactive user may place an interactive program inside a loop.  If
 * the interactive program catches interrupts, the user doesn't want
 * these interrupts to also abort the loop.  The approach we take here
 * is to have the shell ignore interrupt signals while waiting for a
 * forground process to terminate, and then send itself an interrupt
 * signal if the child process was terminated by an interrupt signal.
 * Unfortunately, some programs want to do a bit of cleanup and then
 * exit on interrupt; unless these processes terminate themselves by
 * sending a signal to themselves (instead of calling exit) they will
 * confuse this approach.
 */

int
waitforjob(jp)
	register struct job *jp;
	{
#if JOBS
	int mypgrp = getpgrp(0);
#endif
	int status;
	int st;

	INTOFF;
	TRACE(("waitforjob(%%%d) called\n", jp - jobtab + 1));
	while (jp->state == 0 && dowait(1, jp) != -1) ;
#if JOBS
	if (jp->jobctl) {
		if (ioctl(2, TIOCSPGRP, (char *)&mypgrp) < 0)
			error("TIOCSPGRP failed, errno=%d\n", errno);
	}
	if (jp->state == JOBSTOPPED)
		curjob = jp - jobtab + 1;
#endif
	status = jp->ps[jp->nprocs - 1].status;
	/* convert to 8 bits */
	if ((status & 0xFF) == 0)
		st = status >> 8 & 0xFF;
#if JOBS
	else if ((status & 0xFF) == 0177)
		st = (status >> 8 & 0x7F) + 128;
#endif
	else
		st = (status & 0x7F) + 128;
	if (! JOBS || jp->state == JOBDONE)
		freejob(jp);
	CLEAR_PENDING_INT;
	if ((status & 0x7F) == SIGINT)
		kill(getpid(), SIGINT);
	INTON;
	return st;
}



/*
 * Wait for a process to terminate.
 */

STATIC int
dowait(block, job)
	struct job *job;
	{
	int pid;
	int status;
	struct procstat *sp;
	struct job *jp;
	struct job *thisjob;
	int done;
	int stopped;
	int core;

	TRACE(("dowait(%d) called\n", block));
	do {
		pid = waitproc(block, &status);
		TRACE(("wait returns %d, status=%d, errno=%d\n",
				pid, status, errno));
	} while (pid == -1 && errno == EINTR);
	if (pid <= 0)
		return pid;
	INTOFF;
	thisjob = NULL;
	for (jp = jobtab ; jp < jobtab + njobs ; jp++) {
		if (jp->used) {
			done = 1;
			stopped = 1;
			for (sp = jp->ps ; sp < jp->ps + jp->nprocs ; sp++) {
				if (sp->pid == -1)
					continue;
				if (sp->pid == pid) {
					TRACE(("Changin status of proc %d from 0x%x to 0x%x\n", pid, sp->status, status));
					sp->status = status;
					thisjob = jp;
				}
				if (sp->status == -1)
					stopped = 0;
				else if ((sp->status & 0377) == 0177)
					done = 0;
			}
			if (stopped) {		/* stopped or done */
				int state = done? JOBDONE : JOBSTOPPED;
				if (jp->state != state) {
					TRACE(("Job %d: changing state from %d to %d\n", jp - jobtab + 1, jp->state, state));
					jp->state = state;
#if JOBS
					if (done && curjob == jp - jobtab + 1)
						curjob = 0;		/* no current job */
#endif
				}
			}
		}
	}
	INTON;
	if (! rootshell || ! iflag || (job && thisjob == job)) {
#if JOBS
		if ((status & 0xFF) == 0177)
			status >>= 8;
#endif
		core = status & 0x80;
		status &= 0x7F;
		if (status != 0 && status != SIGINT && status != SIGPIPE) {
			if (thisjob != job)
				outfmt(out2, "%d: ", pid);
#if JOBS
			if (status == SIGTSTP && rootshell && iflag)
				outfmt(out2, "%%%d ", job - jobtab + 1);
#endif
			if (status <= MAXSIG && sigmesg[status])
				out2str(sigmesg[status]);
			else
				outfmt(out2, "Signal %d", status);
			if (core)
				out2str(" - core dumped");
			out2c('\n');
			flushout(&errout);
		} else {
			TRACE(("Not printing status: status=%d\n", status));
		}
	} else {
		TRACE(("Not printing status, rootshell=%d, job=0x%x\n", rootshell, job));
		if (thisjob)
			thisjob->changed = 1;
	}
	return pid;
}



/*
 * Do a wait system call.  If job control is compiled in, we accept
 * stopped processes.  If block is zero, we return a value of zero
 * rather than blocking.
 *
 * System V doesn't have a non-blocking wait system call.  It does
 * have a SIGCLD signal that is sent to a process when one of it's
 * children dies.  The obvious way to use SIGCLD would be to install
 * a handler for SIGCLD which simply bumped a counter when a SIGCLD
 * was received, and have waitproc bump another counter when it got
 * the status of a process.  Waitproc would then know that a wait
 * system call would not block if the two counters were different.
 * This approach doesn't work because if a process has children that
 * have not been waited for, System V will send it a SIGCLD when it
 * installs a signal handler for SIGCLD.  What this means is that when
 * a child exits, the shell will be sent SIGCLD signals continuously
 * until is runs out of stack space, unless it does a wait call before
 * restoring the signal handler.  The code below takes advantage of
 * this (mis)feature by installing a signal handler for SIGCLD and
 * then checking to see whether it was called.  If there are any
 * children to be waited for, it will be.
 *
 * If neither SYSV nor BSD is defined, we don't implement nonblocking
 * waits at all.  In this case, the user will not be informed when
 * a background process until the next time she runs a real program
 * (as opposed to running a builtin command or just typing return),
 * and the jobs command may give out of date information.
 */

#ifdef SYSV
STATIC int gotsigchild;

STATIC int onsigchild() {
	gotsigchild = 1;
}
#endif


STATIC int
waitproc(block, status)
	int *status;
	{
#ifdef BSD
	int flags;

#if JOBS
	flags = WUNTRACED;
#else
	flags = 0;
#endif
	if (block == 0)
		flags |= WNOHANG;
	return wait3((union wait *)status, flags, (struct rusage *)NULL);
#else
#ifdef SYSV
	int (*save)();

	if (block == 0) {
		gotsigchild = 0;
		save = signal(SIGCLD, onsigchild);
		signal(SIGCLD, save);
		if (gotsigchild == 0)
			return 0;
	}
	return wait(status);
#else
#if POSIX
	return waitpid(-1, status, block == 0 ? WNOHANG : 0);
#else
	if (block == 0)
		return 0;
	return wait(status);
#endif
#endif
#endif
}



/*
 * Return a string identifying a command (to be printed by the
 * jobs command.
 */

STATIC char *cmdnextc;
STATIC int cmdnleft;
STATIC void cmdtxt(), cmdputs();

STATIC char *
commandtext(n)
	union node *n;
	{
	char *name;

	cmdnextc = name = ckmalloc(50);
	cmdnleft = 50 - 4;
	cmdtxt(n);
	*cmdnextc = '\0';
	return name;
}


STATIC void
cmdtxt(n)
	union node *n;
	{
	union node *np;
	struct nodelist *lp;
	char *p;
	int i;
	char s[2];

	if (n == NULL) return;

	switch (n->type) {
	case NSEMI:
		cmdtxt(n->nbinary.ch1);
		cmdputs("; ");
		cmdtxt(n->nbinary.ch2);
		break;
	case NAND:
		cmdtxt(n->nbinary.ch1);
		cmdputs(" && ");
		cmdtxt(n->nbinary.ch2);
		break;
	case NOR:
		cmdtxt(n->nbinary.ch1);
		cmdputs(" || ");
		cmdtxt(n->nbinary.ch2);
		break;
	case NPIPE:
		for (lp = n->npipe.cmdlist ; lp ; lp = lp->next) {
			cmdtxt(lp->n);
			if (lp->next)
				cmdputs(" | ");
		}
		break;
	case NSUBSHELL:
		cmdputs("(");
		cmdtxt(n->nredir.n);
		cmdputs(")");
		break;
	case NREDIR:
	case NBACKGND:
		cmdtxt(n->nredir.n);
		break;
	case NIF:
		cmdputs("if ");
		cmdtxt(n->nif.test);
		cmdputs("; then ");
		cmdtxt(n->nif.ifpart);
		cmdputs("...");
		break;
	case NWHILE:
		cmdputs("while ");
		goto until;
	case NUNTIL:
		cmdputs("until ");
until:
		cmdtxt(n->nbinary.ch1);
		cmdputs("; do ");
		cmdtxt(n->nbinary.ch2);
		cmdputs("; done");
		break;
	case NFOR:
		cmdputs("for ");
		cmdputs(n->nfor.var);
		cmdputs(" in ...");
		break;
	case NCASE:
		cmdputs("case ");
		cmdputs(n->ncase.expr->narg.text);
		cmdputs(" in ...");
		break;
	case NDEFUN:
		cmdputs(n->narg.text);
		cmdputs("() ...");
		break;
	case NCMD:
		for (np = n->ncmd.args ; np ; np = np->narg.next) {
			cmdtxt(np);
			if (np->narg.next)
				cmdputs(" ");
		}
		for (np = n->ncmd.redirect ; np ; np = np->nfile.next) {
			cmdputs(" ");
			cmdtxt(np);
		}
		break;
	case NARG:
		cmdputs(n->narg.text);
		break;
	case NTO:
		p = ">";  i = 1;  goto redir;
	case NAPPEND:
		p = ">>";  i = 1;  goto redir;
	case NTOFD:
		p = ">&";  i = 1;  goto redir;
	case NFROM:
		p = "<";  i = 0;  goto redir;
	case NFROMFD:
		p = "<&";  i = 0;  goto redir;
redir:
		if (n->nfile.fd != i) {
			s[0] = n->nfile.fd + '0';
			s[1] = '\0';
			cmdputs(s);
		}
		cmdputs(p);
		if (n->type == NTOFD || n->type == NFROMFD) {
			s[0] = n->ndup.dupfd + '0';
			s[1] = '\0';
			cmdputs(s);
		} else {
			cmdtxt(n->nfile.fname);
		}
		break;
	case NHERE:
	case NXHERE:
		cmdputs("<<...");
		break;
	default:
		cmdputs("???");
		break;
	}
}



STATIC void
cmdputs(s)
	char *s;
	{
	register char *p, *q;
	register char c;
	int subtype = 0;

	if (cmdnleft <= 0)
		return;
	p = s;
	q = cmdnextc;
	while ((c = *p++) != '\0') {
		if (c == CTLESC)
			*q++ = *p++;
		else if (c == CTLVAR) {
			*q++ = '$';
			if (--cmdnleft > 0)
				*q++ = '{';
			subtype = *p++;
		} else if (c == '=' && subtype != 0) {
			*q++ = "}-+?="[(subtype & VSTYPE) - VSNORMAL];
			subtype = 0;
		} else if (c == CTLENDVAR) {
			*q++ = '}';
		} else if (c == CTLBACKQ | c == CTLBACKQ+CTLQUOTE)
			cmdnleft++;		/* ignore it */
		else
			*q++ = c;
		if (--cmdnleft <= 0) {
			*q++ = '.';
			*q++ = '.';
			*q++ = '.';
			break;
		}
	}
	cmdnextc = q;
}