Segmentation Fault when enabling --py-call-uwsgi-fork-hooks with Python 3.12 + Sentry SDK

[Den-Varenik]

Description

Running uWSGI with both --enable-threads and --py-call-uwsgi-fork-hooks (as recommended by [Sentry’s WSGI docs](https://docs.sentry.io/platforms/python/integrations/wsgi/#behavior)) causes a Segmentation Fault at startup.

Without --py-call-uwsgi-fork-hooks, uWSGI starts, but Sentry warns about unsupported preforking/thread mode.

---

Environment

• OS: macOS 14.6 (Darwin Kernel 24.6.0, arm64, Apple Silicon M2 Pro)
• Python: 3.12.3
• uWSGI: 2.0.30 (compiled with Apple LLVM 17.0.0, clang-1700.0.13.5)
• sentry-sdk: 2.37.1
• flask: 3.1.2

---

Steps to Reproduce

1. Install dependencies:

   pip install flask==3.1.2 sentry-sdk==2.37.1 uwsgi==2.0.30
   

2. Create app.py:

   from flask import Flask
   import sentry_sdk
   from sentry_sdk.integrations.flask import FlaskIntegration
   
   app = Flask(__name__)
   
   sentry_sdk.init(
       dsn="your_sdk_dsn",
       integrations=[FlaskIntegration()],
       traces_sample_rate=0.2,
       profiles_sample_rate=0.1,
       environment="test",
       send_default_pii=False,
   )
   
   @app.route("/")
   def hello_world():
       return "Hello World!"
   
   if __name__ == "__main__":
       app.run()
   

3. Run uWSGI:

   uwsgi \
     --http=0.0.0.0:8080 \
     --chdir=$(pwd) \
     --mount /=app:app \
     --processes=4 \
     --threads=2 \
     --max-requests=1000 \
     --master \
     --die-on-term \
     --enable-threads \
     --py-call-uwsgi-fork-hooks
   

---

Expected Behavior

• uWSGI should start normally with both options enabled.
• Sentry integration should work without warnings or crashes.

---

Actual Behavior

• uWSGI crashes immediately with a segmentation fault.

Backtrace excerpt:

!!! uWSGI process 92612 got Segmentation Fault !!!
*** backtrace of 92612 ***
0   uwsgi                               0x0000000104e091a0 uwsgi_backtrace + 52
1   uwsgi                               0x0000000104e096a4 uwsgi_segfault + 56
2   libsystem_platform.dylib            0x00000001965b96a4 _sigtramp + 56
3   libpython3.12.dylib                 0x000000010591a6b0 _PyObject_Malloc + 32
4   libpython3.12.dylib                 0x0000000105942290 PyUnicode_New + 200
5   libpython3.12.dylib                 0x000000010594bc84 unicode_decode_utf8 + 244
6   libpython3.12.dylib                 0x00000001059e8bd8 PyImport_ImportModule + 16
7   uwsgi                               0x0000000104e1ef5c uwsgi_uwsgi_loader + 32
8   uwsgi                               0x0000000104e1e730 init_uwsgi_app + 852
9   uwsgi                               0x0000000104e1b938 uwsgi_python_mount_app + 172
10  uwsgi                               0x0000000104e0d330 uwsgi_init_all_apps + 384
11  uwsgi                               0x0000000104e0cc28 uwsgi_start + 2944
12  uwsgi                               0x0000000104e0b3c0 uwsgi_setup + 7076
13  uwsgi                               0x0000000104e09818 main + 12
14  dyld                                0x00000001961deb98 start + 6076
*** end of backtrace ***

---

Notes

• Without --py-call-uwsgi-fork-hooks, Sentry logs:

  IMPORTANT: We detected the use of uWSGI in preforking mode without thread support. 
  This might lead to crashing workers. Please run uWSGI with both 
  "--enable-threads" and "--py-call-uwsgi-fork-hooks" for full support.
  

• With the flag, uWSGI segfaults immediately.

• Reproducible with a minimal Flask + Sentry app on Python 3.12.

---

Question for Maintainers

• Is this a bug in uWSGI’s fork hooks implementation (possibly related to Python 3.12)?
• Or is there a known limitation/workaround for using --py-call-uwsgi-fork-hooks?