Fix error handling in docs

docs/tools/util.py

@@ -2,6 +2,7 @@ import contextlib
 import multiprocessing
 import os
 import shutil
+import sys
 import tempfile
 import threading
 
@@ -26,9 +27,15 @@ def autoremoved_file(path):
 
 def run_function_in_parallel(func, args_list, threads=False):
     processes = []
+    exit_code = 0
     for task in args_list:
         cls = threading.Thread if threads else multiprocessing.Process
         processes.append(cls(target=func, args=task))
         processes[-1].start()
     for process in processes:
         process.join()
+        if not threads:
+            if process.exitcode and not exit_code:
+                exit_code = process.exitcode
+    if exit_code:
+        sys.exit(exit_code)