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Question

I am using cherrypy as a webserver. It gives good performance for my application but there is a very big problem with it. cherrypy crashes after couple of hours stating that it could not create a socket as there are too many files open:

[21/Oct/2008:12:44:25] ENGINE HTTP Server 
cherrypy._cpwsgi_server.CPWSGIServer(('0.0.0.0', 8080)) shut down    
[21/Oct/2008:12:44:25] ENGINE Stopped thread '_TimeoutMonitor'.    
[21/Oct/2008:12:44:25] ENGINE Stopped thread 'Autoreloader'.    
[21/Oct/2008:12:44:25] ENGINE Bus STOPPED    
[21/Oct/2008:12:44:25] ENGINE Bus EXITING    
[21/Oct/2008:12:44:25] ENGINE Bus EXITED    
Exception in thread HTTPServer Thread-3:    
Traceback (most recent call last):    
  File "/usr/lib/python2.3/threading.py", line 436, in __bootstrap    
    self.run()    
  File "/usr/lib/python2.3/threading.py", line 416, in run   
    self.__target(*self.__args, **self.__kwargs)    
  File "/usr/lib/python2.3/site-packages/cherrypy/process/servers.py", line 73, in 
_start_http_thread    
    self.httpserver.start()    
  File "/usr/lib/python2.3/site-packages/cherrypy/wsgiserver/__init__.py", line 1388, in start
    self.tick()    
  File "/usr/lib/python2.3/site-packages/cherrypy/wsgiserver/__init__.py", line 1417, in tick    
    s, addr = self.socket.accept()    
  File "/usr/lib/python2.3/socket.py", line 167, in accept    
    sock, addr = self._sock.accept()    
error: (24, 'Too many open files')    
[21/Oct/2008:12:44:25] ENGINE Waiting for child threads to terminate..

I tried to figure out what was happening. My application does not open any file or any socket etc. My file only opens couple of berkeley dbs. I investigated this issue further. I saw the file descriptors used by my cherrypy process with id 4536 in /proc/4536/fd/ Initially there were new sockets created and cleaned up properly but after an hour I found that it had about 509 sockets that were not cleaned. All the sockets were in CLOSE_WAIT state. I got this information using the following command:

netstat -ap | grep "4536" | grep CLOSE_WAIT | wc -l

CLOSE_WAIT state means that the remote client has closed the connection. Why is cherrypy then not closing the socket and free the file descriptors? What can I do to resolve the problem?

I tried to play with the following:

cherrypy.config.update({'server.socketQueueSize': '10'})

I thought that this would restrict the number of sockets open at any time to 10 but it was not effective at all. This is the only config I have set, so , rest of the configs hold their default values.

Could somebody throw light on this? Do you think its a bug in cherrypy? How can I resolve it? Is there a way I can close these sockets myself?

Following is my systems info:

CherryPy-3.1.0

python 2.3.4

Red Hat Enterprise Linux ES release 4 (Nahant Update 7)

Thanks in advance!

Answer 1

I imagine you're storing (in-memory) some piece of data which has a reference to the socket; if you store the request objects anywhere, for instance, that would likely do it.

The last-ditch chance for sockets to be closed is when they're garbage-collected; if you're doing anything that would prevent garbage collection from reaching them, there's your problem. I suggest that you try to reproduce with a Hello World program written in CherryPy; if you can't reproduce there, you know it's in your code -- look for places where you're persisting information which could (directly or otherwise) reference the socket.