Fix Sphinx crashes on parallel build with an extension which raises unserializable exception

CHANGES

@@ -27,6 +27,8 @@ Bugs fixed
 * #3294: ``add_latex_package()`` make crashes non-LaTeX builders
 * The caption of table are rendered as invalid HTML (refs: #3287)
 * #3268: Sphinx crashes with requests package from Debian jessie
+* #3284: Sphinx crashes on parallel build with an extension which raises
+  unserializable exception
 
 
 Release 1.5.1 (released Dec 13, 2016)

sphinx/errors.py

@@ -71,10 +71,9 @@ class SphinxParallelError(SphinxError):
 
     category = 'Sphinx parallel build error'
 
-    def __init__(self, orig_exc, traceback):
-        self.orig_exc = orig_exc
+    def __init__(self, message, traceback):
+        self.message = message
         self.traceback = traceback
 
     def __str__(self):
-        return traceback.format_exception_only(
-            self.orig_exc.__class__, self.orig_exc)[0].strip()
+        return self.message

sphinx/util/parallel.py

@@ -73,7 +73,8 @@ class ParallelTasks(object):
                 ret = func(arg)
             pipe.send((False, ret))
         except BaseException as err:
-            pipe.send((True, (err, traceback.format_exc())))
+            errmsg = traceback.format_exception_only(err.__class__, err)[0].strip()
+            pipe.send((True, (errmsg, traceback.format_exc())))
 
     def add_task(self, task_func, arg=None, result_func=None):
         tid = self._taskid