#27647: Django segmentation faults with server autoreload enabled on Windows 10
-------------------------------------+-------------------------------------
               Reporter:  Aleksi     |          Owner:  nobody
  Häkli                              |
                   Type:             |         Status:  new
  Uncategorized                      |
              Component:  Core       |        Version:  1.10
  (Management commands)              |       Keywords:  runserver
               Severity:  Normal     |  autoreload autoreload.py noreload
                                     |  restart_with_reloader segfault
                                     |  segmentation fault ucrtbase.dll
           Triage Stage:             |  threading
  Unreviewed                         |      Has patch:  0
    Needs documentation:  0          |    Needs tests:  0
Patch needs improvement:  0          |  Easy pickings:  0
                  UI/UX:  0          |
-------------------------------------+-------------------------------------
 Django `runserver` segfaults with autoreload enabled on the `os.spawnve`
 call on Python 3.5 and Python 3.6.

 The problem is apparently on this line:

 
https://github.com/django/django/blob/b79fc11d730b5beff92e9dd8853a61524cdeffe3/django/utils/autoreload.py#L290

 ----

 **Discussion**

 I have run Django 1.8, 1.9 and 1.10 on multiple Python versions on top of
 Windows 10 64-bit on different computers.  Starting with Python 3.5 and
 Python 3.6 I have reproduced a consistent segmentation fault on the
 `runserver` command with both 32-bit and 64-bit Pythons. This has happened
 for several months. `python manage.py migrate` and other commands work
 well and consistently. `python manage.py runserver` is the ONLY command
 that segmentation faults and does NOT do this with `--noreload` option.
 Today I dug a bit deeper on the cause of the segmentation fault.

 As a note, I have also run Django on top of Python 3.4 and at least the
 32-bit distribution, for whatever reason, tends not to cause errors like
 these. This is, however, just my butt-feeling, as we say in Finland, and I
 have not measured the stuff for a small while.

 ----

 **Demonstration**

 This example is run with `virtualenvwrapper` installed virtual environment
 with Python 3.6.0 32-bit with the latest available `Microsoft Visual C++
 2015 Redistributable (x86) - 14.0.23026` downloaded and patched today on
 Windows 10 64-bit, so I expect my computer is up to date. Program versions
 and tracebacks following.

 ----

 **Python installation**

 {{{
 USER@COMPUTER MINGW32 ~
 $ python
 Python 3.6.0 (v3.6.0:41df79263a11, Dec 23 2016, 07:18:10) [MSC v.1900 32
 bit (Intel)] on win32
 }}}

 {{{
 USER@COMPUTER MINGW32 ~
 $ pip freeze  # global dependencies
 pbr==1.10.0
 six==1.10.0
 stevedore==1.19.1
 virtualenv==15.1.0
 virtualenv-clone==0.2.6
 virtualenvwrapper==4.7.2
 }}}

 ----

 **`gdb` traceback** on the error which identifies `ucrtbase.dll` and
 `wdupenv_s` as the evil party:

 {{{
 (demo)
 USER@COMPUTER MINGW32 ~/Documents/projects/demo (master)
 $ gdb python
 GNU gdb (GDB) 7.6.1
 Copyright (C) 2013 Free Software Foundation, Inc.
 License GPLv3+: GNU GPL version 3 or later
 <http://gnu.org/licenses/gpl.html>
 This is free software: you are free to change and redistribute it.
 There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
 and "show warranty" for details.
 This GDB was configured as "mingw32".
 For bug reporting instructions, please see:
 <http://www.gnu.org/software/gdb/bugs/>...
 Reading symbols from
 C:\Users\USER\.virtualenvs\demo\Scripts\python.exe...(no debugging symbols
 found)...done.
 (gdb) run manage.py runserver
 Starting program: C:\Users\USER\.virtualenvs\demo\Scripts/python.exe
 manage.py runserver
 [New Thread 6876.0x2a18]
 [New Thread 6876.0x13f4]
 [New Thread 6876.0x25d0]
 [New Thread 6876.0x2a64]

 Program received signal SIGSEGV, Segmentation fault.
 0x77cebd9e in wdupenv_s () from C:\WINDOWS\SysWoW64\ucrtbase.dll
 (gdb)
 }}}

 ----

 **`faulthandler` traceback** with a vanilla `manage.py` script with
 `faulthandler` enabled with `faulthandler.enable()` which traces the
 Django error back to `autoreload.py`:

 {{{
 (demo)
 USER@COMPUTER MINGW32 ~/Documents/projects/demo (master)
 $ python manage.py runserver

 Windows fatal exception: access violation

 Current thread 0x00001b6c (most recent call first):
   File "C:\Users\USER\.virtualenvs\demo\lib\site-
 packages\django\utils\autoreload.py", line 290 in restart_with_reloader
   File "C:\Users\USER\.virtualenvs\demo\lib\site-
 packages\django\utils\autoreload.py", line 304 in python_reloader
   File "C:\Users\USER\.virtualenvs\demo\lib\site-
 packages\django\utils\autoreload.py", line 333 in main
   File "C:\Users\USER\.virtualenvs\demo\lib\site-
 packages\django\core\management\commands\runserver.py", line 106 in run
   File "C:\Users\USER\.virtualenvs\demo\lib\site-
 packages\django\core\management\commands\runserver.py", line 97 in handle
   File "C:\Users\USER\.virtualenvs\demo\lib\site-
 packages\django\core\management\base.py", line 345 in execute
   File "C:\Users\USER\.virtualenvs\demo\lib\site-
 packages\django\core\management\commands\runserver.py", line 58 in execute
   File "C:\Users\USER\.virtualenvs\demo\lib\site-
 packages\django\core\management\base.py", line 294 in run_from_argv
   File "C:\Users\USER\.virtualenvs\demo\lib\site-
 packages\django\core\management\__init__.py", line 359 in execute
   File "C:\Users\USER\.virtualenvs\demo\lib\site-
 packages\django\core\management\__init__.py", line 367 in
 execute_from_command_line
   File "manage.py", line 26 in <module>
 Segmentation fault
 }}}

--
Ticket URL: <https://code.djangoproject.com/ticket/27647>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.

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