Improve Eshell's behavior when waiting for processes

This has a few benefits.  First, it fixes a race condition when killing
old processes in 'eshell-command'.  Second, the "wait" built-in command
is now more useful.  Finally, killing processes when exiting Eshell (via
'eshell-round-robin-kill') should be much faster.

* lisp/eshell/esh-proc.el (esh-opt): Require.
(eshell-wait-for-process): Make obsolete in favor of...
(eshell-wait-for-processes): ... this.  Accept a timeout and support
PIDs.  Update callers.
(eshell/wait): New implementation accepting -t/--timeout.
(eshell-round-robin-kill): Use 'eshell-wait-for-processes'.

* lisp/eshell/eshell.el (eshell-command): Use 'eshell-round-robin-kill'.

* doc/misc/eshell.texi (List of Built-ins): Document the new "wait"
behavior.

* etc/NEWS: Announce this change.

1 files changed, 5 insertions, 2 deletions

diff --git a/doc/misc/eshell.texi b/doc/misc/eshell.texi
index 69f94fab469..8547131194e 100644
--- a/doc/misc/eshell.texi
+++ b/doc/misc/eshell.texi
@@ -1201,8 +1201,11 @@ or a string, referring to an environment variable.
 
 @cmindex wait
 @cindex processes, waiting for
-@item wait [@var{process}]@dots{}
-Wait until each specified @var{process} has exited.
+@item wait [-t @var{timeout}] [@var{process}]@dots{}
+Wait until each specified @var{process} has exited.  Processes can
+either be process objects (@pxref{Processes, , , elisp, GNU Emacs Lisp
+Reference Manual}) or integer PIDs.  If you pass @code{-t} or
+@code{--timeout}, wait at most that many seconds before exiting.
 
 @cmindex which
 @item which @var{command}@dots{}