Re: zsh behavior when fork() failed

[Bart Schaefer <schaefer@brasslantern.com>]

On Feb 25, 10:03pm, Dipak Gaigole wrote:
} Subject: Re: zsh behavior when fork() failed
}
} > Section 2.8.1 lists command execution failures where a non-interactive
} > shell "shall exit", but fork failure is not among them.
} 
} Got it.

That doesn't mean I didn't miss something.  (I was kind of in a hurry
on Friday ...)

This also raises the question of whether a non-interactive shell should
exit on a botched "exec" (see zsh-workers/30111 and subsequent thread,
and comment on line 3364 excerpted below).

} But I don't want to add a check of $? after each command in
} the scripts specially in cases where scripts are 1000+ lines.

Would "set -e" (setopt err_exit) do what you need?

} Is there any zsh option to make sure script exit when fork fails? Else
} can I patch the zsh code to make script exit on fork failure?

It's entirely possible that "return;" on lines 2818 and 2824 in exec.c:

2814         if (pipe(synch) < 0) {
2815             zerr("pipe failed: %e", errno);
2816             if (oautocont >= 0)
2817                 opts[AUTOCONTINUE] = oautocont;
2818             return;
2819         } else if ((pid = zfork(&bgtime)) == -1) {
2820             close(synch[0]);
2821             close(synch[1]);
2822             if (oautocont >= 0)
2823                 opts[AUTOCONTINUE] = oautocont;
2824             return;
2825         }

should instead behave the way POSIXBUILTINS does:

3362         /*
3363          * For POSIX-compatible behaviour with special
3364          * builtins (including exec which we don't usually
3365          * classify as a builtin) we treat all errors as fatal.
3366          * The "command" builtin is not special so resets this behaviour.
3367          */
3368         if (redir_err || errflag) {
3369             if (!isset(INTERACTIVE)) {
3370                 if (forked)
3371                     _exit(1);
3372                 else
3373                     exit(1);
3374             }
3375             errflag = 1;
3376         }

There are a couple of other cases (e.g., around line 1680) where's also
possible the error should be considered unrecoverable.

That would make a full patch look something like the following (which
still exits with 1, rather than with 128 like bash, but does exit).
The oautocont stuff goes away because it's handled below the "fatal"
label (outside the visible diff context).  The second hunk still might
not cause a proper exit, it's in execpline2() from which it's less clear
to me how to reach the "fatal" condition but it's pretty obvious that
it shouldn't just be falling through in those error states.


Index: Src/exec.c
--- ../zsh-forge/current/Src/exec.c	2012-02-12 13:31:49.000000000 -0800
+++ Src/exec.c	2012-02-26 11:47:48.000000000 -0800
@@ -1617,9 +1617,8 @@
 		 (list_pipe || (pline_level && !(jn->stat & STAT_SUBJOB)))))
 		deletejob(jn, 0);
 	    thisjob = pj;
-
 	}
-	if (slflags & WC_SUBLIST_NOT)
+	if ((slflags & WC_SUBLIST_NOT) && !errflag)
 	    lastval = !lastval;
     }
     if (!pline_level)
@@ -1679,9 +1678,13 @@
 
 	    if (pipe(synch) < 0) {
 		zerr("pipe failed: %e", errno);
+		lastval = errflag = 1;
+		return;
 	    } else if ((pid = zfork(&bgtime)) == -1) {
 		close(synch[0]);
 		close(synch[1]);
+		lastval = errflag = 1;
+		return;
 	    } else if (pid) {
 		char dummy, *text;
 
@@ -2490,7 +2493,7 @@
 		    if (!firstnode(args)) {
 			zerr("exec requires a command to execute");
 			errflag = lastval = 1;
-			return;
+			goto fatal;
 		    }
 		    uremnode(args, firstnode(args));
 		    if (!strcmp(next, "--"))
@@ -2507,12 +2510,12 @@
 				if (!firstnode(args)) {
 				    zerr("exec requires a command to execute");
 				    errflag = lastval = 1;
-				    return;
+				    goto fatal;
 				}
 				if (!nextnode(firstnode(args))) {
 				    zerr("exec flag -a requires a parameter");
 				    errflag = lastval = 1;
-				    return;
+				    goto fatal;
 				}
 				exec_argv0 = (char *)
 				    getdata(nextnode(firstnode(args)));
@@ -2813,15 +2816,12 @@
 
 	if (pipe(synch) < 0) {
 	    zerr("pipe failed: %e", errno);
-	    if (oautocont >= 0)
-		opts[AUTOCONTINUE] = oautocont;
-	    return;
+	    goto fatal;
 	} else if ((pid = zfork(&bgtime)) == -1) {
 	    close(synch[0]);
 	    close(synch[1]);
-	    if (oautocont >= 0)
-		opts[AUTOCONTINUE] = oautocont;
-	    return;
+	    lastval = errflag = 1;
+	    goto fatal;
 	}
 	if (pid) {
 
@@ -3365,6 +3365,7 @@
 	 * classify as a builtin) we treat all errors as fatal.
 	 * The "command" builtin is not special so resets this behaviour.
 	 */
+    fatal:
 	if (redir_err || errflag) {
 	    if (!isset(INTERACTIVE)) {
 		if (forked)