Too many files open when starting and stopping kernel repeatedly

[astrofrog]

The following code:

from IPython.kernel import KernelManager

for i in range(1000):
    km = KernelManager()
    km.start_kernel(extra_arguments=['--pylab=inline'])
    kc = km.client()
    kc.start_channels()
    kc.stop_channels()
    km.shutdown_kernel(now=True)

causes the following exception after ~27 iterations:

Traceback (most recent call last):
  File "test_ipython.py", line 6, in <module>
  File "/Users/tom/Library/Python/2.7/lib/python/site-packages/IPython/kernel/manager.py", line 202, in start_kernel
  File "/Users/tom/Library/Python/2.7/lib/python/site-packages/IPython/kernel/connect.py", line 481, in write_connection_file
  File "/Users/tom/Library/Python/2.7/lib/python/site-packages/IPython/kernel/connect.py", line 110, in write_connection_file
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/socket.py", line 187, in __init__
socket.error: [Errno 24] Too many open files

It looks like some file handles are not getting closed? I had a look and didn't see anything obvious. This is relevant for e.g. runipy because it starts and stops the kernel each time a different notebook is run.

(also, the error occurs even if I set now=False).

[ellisonbg]

I can reproduce. It causes and fatal error in libzmq for me after 21 iterations.

[minrk]

Should be fixed by #4890.

[minrk]

I should also note that OS X has an unusually low FD limit (256 by default, while most other systems use 1024). You can easily push this limit up with ulimit -n 1024.