File descriptors not inherited by child processes in python 3.4

[thunderk]

There was an important change in python 3.4 that seems to break the usage of use_sockets.

Python 3.4 does not allow inheritance of newly created file descriptors to child processes by default : https://docs.python.org/3/whatsnew/3.4.html#whatsnew-pep-446

On linux, when using file descriptors for sockets, only fds 0 through 7 seems to be made available in child process.

I have a circus conf with 4 daemon watchers with use_sockets=True. The first 2 daemons get fd=6 and fd=7 and can open their socket and work with it. The last 2 daemons get fd=8 and fd=9 and get an exception on opening them :

OSError: [Errno 9] Bad file descriptor

[thunderk]

I created a branch to show a potential fix for the problem. This is a quick-and-dirty solution, I want to add unit tests, and check if this is the correct place to change fd inheritance. I'm also don't sure if the 'hasattr' method I use is the best way to find if we need to do this.
https://github.com/thunderk/circus/compare/787-fd-inheritance-py34

[k4nar]

Shouldn't we do it only if "close_fds" is False ?

[tarekziade]

@thunderk I suspect we want to place this code in the sockets module, in the CircusSocket class immediatly after the fd is linked - where we set another flag already

see https://github.com/mozilla-services/circus/blob/master/circus/sockets.py#L71

hasattr is fine I guess

[thunderk]

@tarekziade Thanks, I'll move the code there and open a pull request

@k4nar I won't have access to "close_fds" after the move to sockets module. But I don't think it's a problem, inheritance was the default prior to 3.4 and close_fds should work regardless

[thunderk]

Fix has been merged to master

[iDevPy]

Hi everyone,

I'm trying to run circus with python 3.4.1 and I'm getting this same error.
This is the content of my circus.ini

[circus]
endpoint = tcp://127.0.0.1:5555
pubsub_endpoint = tcp://127.0.0.1:5556
stats_endpoint = tcp://127.0.0.1:5557

[watcher:settings]
cmd = /root/.virtualenvs/myenv/bin/chaussette settings.wsgi.application
args = --backend tornado --fd $(circus.sockets.settings)
use_sockets = True
numprocesses = 3
copy_env = True
virtualenv = /root/.virtualenvs/myenv/

[socket:settings]
host = 0.0.0.0
port = 8080

This is the output of "circusd circus.ini":

(myenv)[root@server django]# circusd circus.ini
2014-09-02 05:13:50 circus[2595] [INFO] Starting master on pid 2595
2014-09-02 05:13:50 circus[2595] [INFO] sockets started
2014-09-02 05:13:50 circus[2595] [INFO] Arbiter now waiting for commands
2014-09-02 05:13:50 circus[2595] [INFO] settings started
2014-09-02 05:13:50 circus[2595] [INFO] circusd-stats started
2014-09-02 05:13:51 circus[2602] [INFO] Starting the stats streamer
2014-09-02 05:13:51 [2599] [INFO] Application is <django.core.handlers.wsgi.WSGIHandler object at 0x7f21f762b208>
2014-09-02 05:13:51 [2599] [INFO] Serving on fd://7
2014-09-02 05:13:51 [2599] [INFO] Using <class 'chaussette.backend._tornado.Server'> as a backend
Traceback (most recent call last):
File "/root/.virtualenvs/myenv/bin/chaussette", line 9, in
load_entry_point('chaussette==1.2', 'console_scripts', 'chaussette')()
File "/root/.virtualenvs/myenv/lib/python3.4/site-packages/chaussette/server.py", line 203, in main
inner()
File "/root/.virtualenvs/myenv/lib/python3.4/site-packages/chaussette/server.py", line 184, in inner
socket_type=_SOCKET_TYPE[args.socket_type])
File "/root/.virtualenvs/myenv/lib/python3.4/site-packages/chaussette/server.py", line 35, in make_server
server = server_class((host, port), app, **server_class_kwargs)
File "/root/.virtualenvs/myenv/lib/python3.4/site-packages/chaussette/backend/_tornado.py", line 32, in init
set_close_exec(fd)
File "/root/.virtualenvs/myenv/lib/python3.4/site-packages/tornado/platform/posix.py", line 28, in set_close_exec
flags = fcntl.fcntl(fd, fcntl.F_GETFD)
OSError: [Errno 9] Bad file descriptor

And the same error occurs without --backend tornado

[iDevPy]

I fix it adding the code in this page: https://github.com/mozilla-services/circus/pull/800/files