sh: Forget about terminated background processes sooner.

Unless $! has been referenced for a particular job or $! still contains that
job's pid, forget about it after it has terminated. If $! has been
referenced, remember the job until the wait builtin has reported its
completion (either with the pid as parameter or without parameters).

In interactive mode, jobs are forgotten after termination has been reported,
which happens before primary prompts and through the jobs builtin. Even
then, though, remember a job if $! has been referenced.

This is similar to what is suggested by POSIX and should fix most memory
leaks (which also tend to cause sh to use more CPU time) with long running
scripts that start background jobs.

Caveats:
* Repeatedly referencing $! without ever doing 'wait', like
    while :; do foo & echo started foo: $!; sleep 60; done
  will still use a lot of memory and CPU time in the long run.
* The jobs and jobid builtins do not cause a job to be remembered for longer
  like expanding $! does.

PR:		bin/55346

1 files changed, 56 insertions, 5 deletions

diff --git a/bin/sh/jobs.c b/bin/sh/jobs.c
index 29939d1..f55b637 100644
--- a/bin/sh/jobs.c
+++ b/bin/sh/jobs.c
@@ -75,6 +75,7 @@ __FBSDID("$FreeBSD$");
 STATIC struct job *jobtab;	/* array of jobs */
 STATIC int njobs;		/* size of array */
 MKINIT pid_t backgndpid = -1;	/* pid of last background process */
+MKINIT struct job *bgjob = NULL; /* last background process */
 #if JOBS
 STATIC struct job *jobmru;	/* most recently used job list */
 STATIC pid_t initialpgrp;	/* pgrp of shell on invocation */
@@ -183,6 +184,7 @@ INCLUDE <stdlib.h>
 
 SHELLPROC {
 	backgndpid = -1;
+	bgjob = NULL;
 #if JOBS
 	jobctl = 0;
 #endif
@@ -413,7 +415,11 @@ showjobs(int change, int mode)
 			continue;
 		showjob(jp, 0, mode);
 		jp->changed = 0;
-		if (jp->state == JOBDONE) {
+		/* Hack: discard jobs for which $! has not been referenced
+		 * in interactive mode when they terminate.
+		 */
+		if (jp->state == JOBDONE && !jp->remembered &&
+				(iflag || jp != bgjob)) {
 			freejob(jp);
 		}
 	}
@@ -431,6 +437,8 @@ freejob(struct job *jp)
 	int i;
 
 	INTOFF;
+	if (bgjob == jp)
+		bgjob = NULL;
 	for (i = jp->nprocs, ps = jp->ps ; --i >= 0 ; ps++) {
 		if (ps->cmd != nullstr)
 			ckfree(ps->cmd);
@@ -477,12 +485,27 @@ waitcmd(int argc, char **argv)
 #endif
 				else
 					retval = WTERMSIG(status) + 128;
-				if (! iflag)
+				if (! iflag || ! job->changed)
 					freejob(job);
+				else {
+					job->remembered = 0;
+					if (job == bgjob)
+						bgjob = NULL;
+				}
 				in_waitcmd--;
 				return retval;
 			}
 		} else {
+			for (jp = jobtab ; jp < jobtab + njobs; jp++)
+				if (jp->used && jp->state == JOBDONE) {
+					if (! iflag || ! jp->changed)
+						freejob(jp);
+					else {
+						jp->remembered = 0;
+						if (jp == bgjob)
+							bgjob = NULL;
+					}
+				}
 			for (jp = jobtab ; ; jp++) {
 				if (jp >= jobtab + njobs) {	/* no running procs */
 					in_waitcmd--;
@@ -623,6 +646,8 @@ makejob(union node *node __unused, int nprocs)
 						jp[i].next = &jp[jp[i].next -
 						    jobtab];
 #endif
+				if (bgjob != NULL)
+					bgjob = &jp[bgjob - jobtab];
 				/* Relocate `ps' pointers */
 				for (i = 0; i < njobs; i++)
 					if (jp[i].ps == &jobtab[i].ps0)
@@ -644,6 +669,7 @@ makejob(union node *node __unused, int nprocs)
 	jp->changed = 0;
 	jp->nprocs = 0;
 	jp->foreground = 0;
+	jp->remembered = 0;
 #if JOBS
 	jp->jobctl = jobctl;
 	jp->next = NULL;
@@ -821,8 +847,13 @@ forkshell(struct job *jp, union node *n, int mode)
 			pgrp = jp->ps[0].pid;
 		setpgid(pid, pgrp);
 	}
-	if (mode == FORK_BG)
+	if (mode == FORK_BG) {
+		if (bgjob != NULL && bgjob->state == JOBDONE &&
+		    !bgjob->remembered && !iflag)
+			freejob(bgjob);
 		backgndpid = pid;		/* set $! */
+		bgjob = jp;
+	}
 	if (jp) {
 		struct procstat *ps = &jp->ps[jp->nprocs++];
 		ps->pid = pid;
@@ -975,10 +1006,15 @@ dowait(int block, struct job *job)
 				if (jp->state != state) {
 					TRACE(("Job %d: changing state from %d to %d\n", jp - jobtab + 1, jp->state, state));
 					jp->state = state;
+					if (jp != job) {
+						if (done && !jp->remembered &&
+						    !iflag && jp != bgjob)
+							freejob(jp);
 #if JOBS
-					if (done)
-						deljob(jp);
+						else if (done)
+							deljob(jp);
 #endif
+					}
 				}
 			}
 		}
@@ -1074,6 +1110,21 @@ checkzombies(void)
 }
 
 
+int
+backgndpidset(void)
+{
+	return backgndpid != -1;
+}
+
+
+pid_t
+backgndpidval(void)
+{
+	if (bgjob != NULL)
+		bgjob->remembered = 1;
+	return backgndpid;
+}
+
 /*
  * Return a string identifying a command (to be printed by the
  * jobs command.