id summary reporter owner description type status component version severity resolution keywords cc stage has_patch needs_docs needs_tests needs_better_patch easy ui_ux 27647 runserver segfaults with autoreload enabled on Windows 10 Aleksi Häkli nobody "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] Python documentation states that the ''`os.spawnve` function is NOT thread-safe on Windows'' and that the `subprocess` module should be used instead. I hence suspect that a thread that is spawned on reload makes a memory violation and causes a segmentation fault which kills off the server. I propose that `autoreload.py` be refactored to use a thread-safe implementation either by the subprocess module or by other alternative implementation. **Update**: I added a preliminary patch implementation up for review that implements a fix for Python 2.4+ in [https://github.com/django/django/pull/7748] by using the recommended `subprocess.call()` instead of the non-thread-safe `os.spawnve()` which was added in a commit in 2005. ---- **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 gut feeling and I have not looked into the `runserver` error rate on Python 3.4 for a 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 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: ... 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 Segmentation fault }}} " Bug closed Core (Management commands) 1.10 Normal fixed runserver autoreload autoreload.py noreload restart_with_reloader segfault segmentation fault ucrtbase.dll threading Ready for checkin 1 0 0 0 0 0