app crashes with Fatal Python error: ffi.from_handle() detected that the address passed points to garbage shortly after starting only on Windows since 20.4.0

[PawelTroka]

• gevent version: 20.4.0
• Python version: cPython 3.8.2 (tags/v3.8.2:7b3ab59, Feb 25 2020, 23:03:10) [MSC v.1916 64 bit (AMD64)] on win32 downloaded from python.org
• Operating System: Microsoft Windows 10 Version 1903 (OS Build 18362.720)

Description:

Nothing fancy just running an app with Flask, gevent and gevent-websocket (all in their latest versions) and it crashes shortly after running. Sometimes it is nearly instantly, sometimes it takes even several seconds (no longer than a minute though) but it always does exit with error code. Strangely it only happens on Windows - on Linux Ubuntu (through docker) everything is all right. Everything worked OK back on gevent 1.5.0 but this warning (#1564) was written repeatedly.

Fatal Python error: ffi.from_handle() detected that the address passed points to garbage. If it is really the result of ffi.new_handle(), then the Python object has already been garbage collected
Python runtime state: initialized

Thread 0x00004958 (most recent call first):
  File "C:\Users\patr\AppData\Local\Programs\Python\Python38\lib\site-packages\gevent\_threading.py", line 60 in wait
  File "C:\Users\patr\AppData\Local\Programs\Python\Python38\lib\site-packages\gevent\_threading.py", line 146 in get
  File "C:\Users\patr\AppData\Local\Programs\Python\Python38\lib\site-packages\gevent\threadpool.py", line 155 in run

Thread 0x00004ad8 (most recent call first):
  File "C:\Users\patr\AppData\Local\Programs\Python\Python38\lib\site-packages\gevent\_threading.py", line 60 in wait
  File "C:\Users\patr\AppData\Local\Programs\Python\Python38\lib\site-packages\gevent\_threading.py", line 146 in get
  File "C:\Users\patr\AppData\Local\Programs\Python\Python38\lib\site-packages\gevent\threadpool.py", line 155 in run

Current thread 0x0000549c (most recent call first):
  File "C:\Users\patr\AppData\Local\Programs\Python\Python38\lib\site-packages\gevent\_ffi\loop.py", line 264 in python_stop
  File "C:\Users\patr\AppData\Local\Programs\Python\Python38\lib\site-packages\gevent\libuv\loop.py", line 498 in __run_queued_callbacks
  File "C:\Users\patr\AppData\Local\Programs\Python\Python38\lib\site-packages\gevent\libuv\loop.py", line 218 in _run_callbacks
  File "C:\Users\patr\AppData\Local\Programs\Python\Python38\lib\site-packages\gevent\_ffi\loop.py", line 300 in python_prepare_callback
  File "C:\Users\patr\AppData\Local\Programs\Python\Python38\lib\site-packages\gevent\libuv\loop.py", line 542 in run
  File "C:\Users\patr\AppData\Local\Programs\Python\Python38\lib\site-packages\gevent\hub.py", line 618 in run

Process finished with exit code -1073740791 (0xC0000409)

[jamadden]

Can you provide a short, self contained example that reliably crashes? Without being able to reproduce the problem it's very difficult to find and fix. It looks as if a watcher object is still active when it shouldn't be, but beyond that theres not much I can say.

Strangely it only happens on Windows - on Linux Ubuntu (through docker) everything is all right.

The default event loop is different on Windows and Linux. It would be interesting to know if using the libuv-cffi loop on Linux reproduces the crash.

[PawelTroka]

@jamadden Ok, I can try to provide a short, self contained example but this is in proprietary application, so it can take me some time to properly extract that.

[jtc42]

I'm facing the exact same issue. Gevent 20.04, Windows 10. Works fine on WSL2

[susoooon]

from gevent import monkey,pywsgi
monkey.patch_all(thread=False)
from flask import Flask,request
from flask import request, jsonify, json
app = Flask(__name__)

app.config['JSON_AS_ASCII'] = False


@app.route('/helloworld', methods=[ 'POST','GET'])
def hello():
    return "hello world"
if __name__ == '__main__':
    app.run(host="127.0.0.1",port=5000)

when i start flask and request,first time is ok,but second the error happend

[int3l]

Can confirm the same error on Windows 10 (1909) Latest with python 3.8.1 and gevent 20.5.0
As a workaround I should revert back to gevent 1.5.0 until this gets sorted.

Error output for reference:

Fatal Python error: ffi.from_handle() detected that the address passed points to garbage. If it is really the result of ffi.new_handle(), then the Python object has already been garbage collected
Python runtime state: initialized

Thread 0x00000858 (most recent call first):
  File "Z:\Project\env\lib\site-packages\gevent\_threading.py", line 60 in wait
  File "Z:\Project\env\lib\site-packages\gevent\_threading.py", line 146 in get
  File "Z:\Project\env\lib\site-packages\gevent\threadpool.py", line 155 in run

Current thread 0x00002230 (most recent call first):
  File "Z:\Project\env\lib\site-packages\gevent\_ffi\loop.py", line 264 in python_stop
  File "Z:\Project\env\lib\site-packages\gevent\libuv\loop.py", line 498 in __run_queued_callbacks
  File "Z:\Project\env\lib\site-packages\gevent\libuv\loop.py", line 218 in _run_callbacks
  File "Z:\Project\env\lib\site-packages\gevent\_ffi\loop.py", line 300 in python_prepare_callback
  File "Z:\Project\env\lib\site-packages\gevent\libuv\loop.py", line 542 in run
  File "Z:\Project\env\lib\site-packages\gevent\hub.py", line 618 in run

[jamadden]

Fixed in #1602, as best I can tell.