From e900096dc42cd0d590752e00ba3983b4672da806 Mon Sep 17 00:00:00 2001
From: Benjamin Peterson <benjamin@python.org>
Date: Mon, 2 Apr 2012 11:15:17 -0400
Subject: prevent writing to stderr from messing up the exception state (closes
 #14474)

---
 Lib/test/test_thread.py | 24 ++++++++++++++++++++++++
 Misc/NEWS               |  3 +++
 Modules/_threadmodule.c |  3 +++
 3 files changed, 30 insertions(+)

diff --git a/Lib/test/test_thread.py b/Lib/test/test_thread.py
index 894a493..deb4bf3 100644
--- a/Lib/test/test_thread.py
+++ b/Lib/test/test_thread.py
@@ -128,6 +128,30 @@ class ThreadRunningTests(BasicThreadTest):
             time.sleep(0.01)
         self.assertEqual(thread._count(), orig)
 
+    def test_save_exception_state_on_error(self):
+        # See issue #14474
+        def task():
+            started.release()
+            sys.stderr = stderr
+            raise SyntaxError
+        def mywrite(self, *args):
+            try:
+                raise ValueError
+            except ValueError:
+                pass
+            real_write(self, *args)
+        c = thread._count()
+        started = thread.allocate_lock()
+        with support.captured_output("stderr") as stderr:
+            real_write = stderr.write
+            stderr.write = mywrite
+            started.acquire()
+            thread.start_new_thread(task, ())
+            started.acquire()
+            while thread._count() > c:
+                pass
+        self.assertIn("Traceback", stderr.getvalue())
+
 
 class Barrier:
     def __init__(self, num_threads):
diff --git a/Misc/NEWS b/Misc/NEWS
index 2fa911e..3d9b822 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,9 @@ What's New in Python 3.2.4
 Core and Builtins
 -----------------
 
+- Issue #14474: Save and restore exception state in thread.start_new_thread()
+  while writing error message if the thread leaves a unhandled exception.
+
 - Issue #13019: Fix potential reference leaks in bytearray.extend().  Patch
   by Suman Saha.
 
diff --git a/Modules/_threadmodule.c b/Modules/_threadmodule.c
index ea038de..5f76a7b 100644
--- a/Modules/_threadmodule.c
+++ b/Modules/_threadmodule.c
@@ -994,14 +994,17 @@ t_bootstrap(void *boot_raw)
             PyErr_Clear();
         else {
             PyObject *file;
+            PyObject *exc, *value, *tb;
             PySys_WriteStderr(
                 "Unhandled exception in thread started by ");
+            PyErr_Fetch(&exc, &value, &tb);
             file = PySys_GetObject("stderr");
             if (file != NULL && file != Py_None)
                 PyFile_WriteObject(boot->func, file, 0);
             else
                 PyObject_Print(boot->func, stderr, 0);
             PySys_WriteStderr("\n");
+            PyErr_Restore(exc, value, tb);
             PyErr_PrintEx(0);
         }
     }
-- 
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