fix and docs

news/rs.rst

@@ -41,12 +41,15 @@
   in favor of a more general mechanism for dispatching callable aliases
   implemented in the ``ProcProxyThread``  and ``ProcProxy`` classes.
 
-
 **Fixed:**
 
 * May now Crtl-C out of an infinite loop with a subprocess, such as
   ```while True: sleep 1``.
 * Fix for stdin redirects.
 * Backgrounding works with ``$XONSH_STORE_STDOUT``
+* Added a minimum time buffer time for command pipelines to check for
+  if previous commands have executed successfully.  This is helpful
+  for pipelines where the last command takes a long time to start up,
+  such as GNU Parallel.
 
 **Security:** None

xonsh/proc.py

@@ -1476,7 +1476,11 @@ class CommandPipeline:
                 time.sleep(0.1)  # probably not leaving any time soon
                 continue
             elif not check_prev_done:
-                if ()
+                # In the case of pipelines with more than one command
+                # we should the commands a little breathing room time
+                # to start up fully. This is particularly true for
+                # GNU Parallel, which has a long startup time.
+                check_prev_done = (time.time() - self.starttime) > 0.1
             elif self._prev_procs_done():
                 self._close_prev_procs()
                 proc.prevs_are_closed = True