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, 3 insertions, 1 deletions

diff --git a/bin/sh/jobs.h b/bin/sh/jobs.h
index c75c353..8bc1082 100644
--- a/bin/sh/jobs.h
+++ b/bin/sh/jobs.h
@@ -68,6 +68,7 @@ struct job {
 	char used;		/* true if this entry is in used */
 	char changed;		/* true if status has changed */
 	char foreground;	/* true if running in the foreground */
+	char remembered;	/* true if $! referenced */
 #if JOBS
 	char jobctl;		/* job running under job control */
 	struct job *next;	/* job used after this one */
@@ -81,7 +82,6 @@ enum {
 	SHOWJOBS_PGIDS		/* PID of the group leader only */
 };
 
-extern pid_t backgndpid;	/* pid of last background process */
 extern int job_warning;		/* user was warned about stopped jobs */
 extern int in_waitcmd;		/* are we in waitcmd()? */
 extern int in_dowait;		/* are we in dowait()? */
@@ -98,6 +98,8 @@ struct job *makejob(union node *, int);
 pid_t forkshell(struct job *, union node *, int);
 int waitforjob(struct job *, int *);
 int stoppedjobs(void);
+int backgndpidset(void);
+pid_t backgndpidval(void);
 char *commandtext(union node *);
 
 #if ! JOBS