Faulty logic for disabling job control in virtual subshells

[McDutchie]

Job control should be disabled in subshells as it makes no sense there; subshells are never interactive and job control only makes sense on interactive shells. However, for non-forking subshells, ksh currently only disables job control for command substitutions:

ksh/src/cmd/ksh93/sh/subshell.c

Lines 570 to 577 in f207cd5

	if(comsub)
	{
	/* disable job control */
	shp->spid = 0;
	sp->jobcontrol = job.jobcontrol;
	sp->monitor = (sh_isstate(SH_MONITOR)!=0);
	job.jobcontrol=0;
	sh_offstate(SH_MONITOR);

ksh/src/cmd/ksh93/sh/subshell.c

Lines 629 to 636 in f207cd5

	if(comsub)
	{
	/* re-enable job control */
	if(!sp->nofork)
	sh_offstate(SH_NOFORK);
	job.jobcontrol = sp->jobcontrol;
	if(sp->monitor)
	sh_onstate(SH_MONITOR);

This causes "interesting" behaviour, e.g.:

$ (sleep 1 & :)
[1]	25185

This wrongly prints a job number.

$ sleep 10 &
$ (fg)

This waits for sleep to end, but should complain about no job control instead. However:

$ (sleep 10 & fg)
[1]	25144
arch/darwin.i386-64/bin/ksh: fg: No job control

So that's inconsisistent.

Related: #79, #86

---

Also:

$ (sleep 1 &)
$ [1]	25187

This wrongly prints a job number after the prompt, i.e. the job number is printed from a background process! So the main shell forks as well as the background process. That's a separate bug, probably a parser bug causing a double fork, akin to the one I fixed in 1026006.

[McDutchie]

I started a related Austin Group thread. Before applying a fix I want to await the outcome of that discussion.

[McDutchie]

In the meantime, here is a patch to test... it should make both this bug and #86 go away.

diff --git a/src/cmd/ksh93/sh/subshell.c b/src/cmd/ksh93/sh/subshell.c
index 5b12f92..c0eb47b 100644
--- a/src/cmd/ksh93/sh/subshell.c
+++ b/src/cmd/ksh93/sh/subshell.c
@@ -567,14 +567,14 @@ Sfio_t *sh_subshell(Shell_t *shp,Shnode_t *t, volatile int flags, int comsub)
 	jmpval = sigsetjmp(buff.buff,0);
 	if(jmpval==0)
 	{
+		/* disable job control */
+		sp->jobcontrol = job.jobcontrol;
+		sp->monitor = (sh_isstate(SH_MONITOR)!=0);
+		job.jobcontrol = 0;
+		sh_offstate(SH_MONITOR);
 		if(comsub)
 		{
-			/* disable job control */
 			shp->spid = 0;
-			sp->jobcontrol = job.jobcontrol;
-			sp->monitor = (sh_isstate(SH_MONITOR)!=0);
-			job.jobcontrol=0;
-			sh_offstate(SH_MONITOR);
 			sp->pipe = sp;
 			/* save sfstdout and status */
 			sp->saveout = sfswap(sfstdout,NIL(Sfio_t*));
@@ -626,14 +626,14 @@ Sfio_t *sh_subshell(Shell_t *shp,Shnode_t *t, volatile int flags, int comsub)
 	if(!shp->savesig)
 		shp->savesig = -1;
 	nv_restore(sp);
+	/* re-enable job control */
+	if(!sp->nofork)
+		sh_offstate(SH_NOFORK);
+	job.jobcontrol = sp->jobcontrol;
+	if(sp->monitor)
+		sh_onstate(SH_MONITOR);
 	if(comsub)
 	{
-		/* re-enable job control */
-		if(!sp->nofork)
-			sh_offstate(SH_NOFORK);
-		job.jobcontrol = sp->jobcontrol;
-		if(sp->monitor)
-			sh_onstate(SH_MONITOR);
 		if(sp->pipefd>=0)
 		{
 			/* sftmp() file has been returned into pipe */
diff --git a/src/cmd/ksh93/sh/xec.c b/src/cmd/ksh93/sh/xec.c
index a6ad507..58e979f 100644
--- a/src/cmd/ksh93/sh/xec.c
+++ b/src/cmd/ksh93/sh/xec.c
@@ -1633,7 +1633,7 @@ int sh_exec(register const Shnode_t *t, int flags)
 				}
 				if(type&FAMP)
 				{
-					if(sh_isstate(SH_PROFILE) || sh_isstate(SH_INTERACTIVE))
+					if(sh_isstate(SH_PROFILE) || (sh_isstate(SH_INTERACTIVE) && sh_isstate(SH_MONITOR)))
 					{
 						/* print job number */
 #ifdef JOBS

[McDutchie]

My earlier statement:

Job control should be disabled in subshells as it makes no sense there; subshells are never interactive and job control only makes sense on interactive shells.

is wrong. Read Geoff Clare's responses in this Austin Group thread to learn why.

So the patch above is wrong as well.

[McDutchie]

Closing this as my assumption was wrong. Job control in scripts should be fixed though, see #119.