Issue #13813: Embed stringification of remote traceback in local

traceback raised when pool task raises an exception.

Lib/multiprocessing/pool.py

@@ -18,6 +18,7 @@ import queue
 import itertools
 import collections
 import time
+import traceback
 
 from multiprocessing import Process, cpu_count, TimeoutError
 from multiprocessing.util import Finalize, debug
@@ -42,6 +43,29 @@ def mapstar(args):
 def starmapstar(args):
     return list(itertools.starmap(args[0], args[1]))
 
+#
+# Hack to embed stringification of remote traceback in local traceback
+#
+
+class RemoteTraceback(Exception):
+    def __init__(self, tb):
+        self.tb = tb
+    def __str__(self):
+        return self.tb
+
+class ExceptionWithTraceback:
+    def __init__(self, exc, tb):
+        tb = traceback.format_exception(type(exc), exc, tb)
+        tb = ''.join(tb)
+        self.exc = exc
+        self.tb = '\n"""\n%s"""' % tb
+    def __reduce__(self):
+        return rebuild_exc, (self.exc, self.tb)
+
+def rebuild_exc(exc, tb):
+    exc.__cause__ = RemoteTraceback(tb)
+    return exc
+
 #
 # Code run by worker processes
 #
@@ -90,6 +114,7 @@ def worker(inqueue, outqueue, initializer=None, initargs=(), maxtasks=None):
         try:
             result = (True, func(*args, **kwds))
         except Exception as e:
+            e = ExceptionWithTraceback(e, e.__traceback__)
             result = (False, e)
         try:
             put((job, i, result))