33531 with additions: retain status of exited background jobs.

Add linked list of unwaited-for background jobs.
Truncate at value of _SC_CHILD_MAX discarding oldest.
Remove old lastpid_status mechanism for latest exited process only.
Slightly tighten safety of permanently allocated linked lists so
that this doesn't compromise signal handling.

2 files changed, 20 insertions, 4 deletions

diff --git a/Doc/Zsh/builtins.yo b/Doc/Zsh/builtins.yo
index 46f40cc3a..edc335e8b 100644
--- a/Doc/Zsh/builtins.yo
+++ b/Doc/Zsh/builtins.yo
@@ -2059,6 +2059,22 @@ then all currently active child processes are waited for.
 Each var(job) can be either a job specification or the process ID
 of a job in the job table.
 The exit status from this command is that of the job waited for.
+
+It is possible to wait for recent processes (specified by process ID,
+not by job) that were running in the background even if the process has
+exited.  Typically the process ID will be recorded by capturing the
+value of the variable tt($!) immediately after the process has been
+started.  There is a limit on the number of process IDs remembered by
+the shell; this is given by the value of the system configuration
+parameter tt(CHILD_MAX).  When this limit is reached, older process IDs
+are discarded, least recently started processes first.
+
+Note there is no protection against the process ID wrapping, i.e. if the
+wait is not executed soon enough there is a chance the process waited
+for is the wrong one.  A conflict implies both process IDs have been
+generated by the shell, as other processes are not recorded, and that
+the user is potentially interested in both, so this problem is intrinsic
+to process IDs.
 )
 findex(whence)
 item(tt(whence) [ tt(-vcwfpams) ] var(name) ...)(
diff --git a/Doc/Zsh/options.yo b/Doc/Zsh/options.yo
index 068a253ac..452b258b4 100644
--- a/Doc/Zsh/options.yo
+++ b/Doc/Zsh/options.yo
@@ -1434,10 +1434,10 @@ shell is saved for output within a subshell (for example, within a
 pipeline).  When the option is set, the output of tt(jobs) is empty
 until a job is started within the subshell.
 
-When the option is set, it becomes possible to use the tt(wait) builtin to
-wait for the last job started in the background (as given by tt($!)) even
-if that job has already exited.  This works even if the option is turned
-on temporarily around the use of the tt(wait) builtin.
+In previous versions of the shell, it was necessary to enable
+tt(POSIX_JOBS) in order for the builtin command tt(wait) to return the
+status of background jobs that had already exited.  This is no longer
+the case.
 )
 enditem()