WARNING: gevent: Unable to dereference handle; not stopping watcher. Native resources may leak.

[SteffRainville]

• gevent version: 1.5.0 downloaded with pipenv
• Python version: 3.8.1 downloaded from python.org"
• Operating System: Windows 10 Pro build 18363 on Ryzen 9 3900X

Description:

trying to run a very simple background job with Greenlet.spawn and keep getting this warning whenever I do a simple http query in Bottle 0.12.18

WARNING: gevent: Unable to dereference handle; not stopping watcher. Native resources may leak. This is most likely a bug in gevent.

Below minimal program to reproduce bug at will

just localhost:8080/hello

What I've run:

from gevent import monkey; monkey.patch_all()
from gevent import Greenlet
import random
import time
import bottle

from bottle import Bottle, run
app = Bottle()

def get_random():
    while True:
        a = random.randrange(1,6)
        print(a)
        time.sleep(5)

Greenlet.spawn(get_random)

@app.route('/hello')
def hello():
    return "Hello World!"

run(app, host='localhost', port=8080)

[jamadden]

I am unable to reproduce that on a POSIX system using libuv. In fact, I can't find that the method in question is ever even called: bottle never closes its socket so the listener is never stopped.

Can you modify AbstractCallbacks.python_stop() in gevent/_ffi/loop.py to print the current traceback when it emits that warning?

[SteffRainville]

You may have to F5 (refresh ) 4 to 5 times to have the error in Chrome but happens all the time in Edge.

I've added traceback.print_exc(file=sys.stdout) in about 20 places after all except statement but can not manage to print the stack when the Warning is displayed.

[jamadden]

I've added traceback.print_exc(file=sys.stdout) in about 20 places after all except statement but can not manage to print the stack when the Warning is displayed.

There's no active exception at that time, so print_exc won't do anything. You just want print_stack.

[SteffRainville]

I also just confirmed that I can not reproduce on mac.

WARNING: gevent: Unable to dereference handle; not stopping watcher. Native resources may leak. This is most likely a bug in gevent.

  File "C:\Users\steph\.virtualenvs\testbottle-5QKBI09C\lib\site-packages\gevent\hub.py", line 618, in run
    loop.run()
  File "C:\Users\steph\.virtualenvs\testbottle-5QKBI09C\lib\site-packages\gevent\libuv\loop.py", line 511, in run
    ran_status = libuv.uv_run(self._ptr, run_mode)
  File "C:\Users\steph\.virtualenvs\testbottle-5QKBI09C\lib\site-packages\gevent\_ffi\loop.py", line 302, in python_prepare_callback
    loop._run_callbacks()
  File "C:\Users\steph\.virtualenvs\testbottle-5QKBI09C\lib\site-packages\gevent\libuv\loop.py", line 208, in _run_callbacks
    self._prepare_ran_callbacks = self.__run_queued_callbacks()
  File "C:\Users\steph\.virtualenvs\testbottle-5QKBI09C\lib\site-packages\gevent\libuv\loop.py", line 467, in __run_queued_callbacks
    _callbacks.python_stop(None)
  File "C:\Users\steph\.virtualenvs\testbottle-5QKBI09C\lib\site-packages\gevent\_ffi\loop.py", line 259, in python_stop
    traceback.print_stack()

[kkzimieras]

I can also confirm I was able to reproduce the issue with gevent version: 1.5.0.
No such warnings if gevent==1.4.0 is installed