Too many open files in python

Question

I wrote kind of a test suite which is heavily file intensive. After some time (2h) I get an IOError: [Errno 24] Too many open files: '/tmp/tmpxsqYPm'. I double checked all file handles whether I close them again. But the error still exists.

I tried to figure out the number of allowed file descriptors using resource.RLIMIT_NOFILE and the number of currently opened file desciptors:

def get_open_fds():

    fds = []
    for fd in range(3,resource.RLIMIT_NOFILE):
            try:
                    flags = fcntl.fcntl(fd, fcntl.F_GETFD)
            except IOError:
                    continue

            fds.append(fd)

    return fds

So if I run the following test:

print get_open_fds()
for i in range(0,100):
    f = open("/tmp/test_%i" % i, "w")
    f.write("test")
    print get_open_fds()

I get this output:

[]
/tmp/test_0
[3]
/tmp/test_1
[4]
/tmp/test_2
[3]
/tmp/test_3
[4]
/tmp/test_4
[3]
/tmp/test_5
[4] ...

That's strange, I expected an increasing number of opened file descriptors. Is my script correct?

I'm using python's logger and subprocess. Could that be the reason for my fd leak?

Thanks, Daniel

Answer 1

Your test script overwrites f each iteration, which means that the file will get closed each time. Both logging to files and subprocess with pipes use up descriptors, which can lead to exhaustion.

Answer 2

The corrected code is:

import resource
import fcntl
import os

def get_open_fds():
    fds = []
    soft, hard = resource.getrlimit(resource.RLIMIT_NOFILE)
    for fd in range(0, soft):
        try:
            flags = fcntl.fcntl(fd, fcntl.F_GETFD)
        except IOError:
            continue
        fds.append(fd)
    return fds

def get_file_names_from_file_number(fds):
    names = []
    for fd in fds:
        names.append(os.readlink('/proc/self/fd/%d' % fd))
    return names

fds = get_open_fds()
print get_file_names_from_file_number(fds)

Answer 3

resource.RLIMIT_NOFILE is indeed 7, but that's an index into resource.getrlimit(), not the limit itself... resource.getrlimit(resource.RLIMIT_NOFILE) is what you want your top range() to be