fork: close all open sockets

POSIX does not include a sensible way to list or close a range of file descriptors.

So we have to loop over the full range (like from 3 to 1023), closing the file descriptors one at a time.

Or, if we have a /proc file system, we can read the list of open file descriptors in /proc/self/fd and close just those. This can be quicker than closing all possible file descriptors.

import osdef close_files(fd_min=3, fd_max=-1):    if os.path.exists('/proc/self/fd'):        close_files_with_procfs(fd_min, fd_max)    else:        close_files_exhaustively(fd_min, fd_max)def close_files_exhaustively(fd_min=3, fd_max=-1):    import resource    fd_top = resource.getrlimit(resource.RLIMIT_NOFILE)[1] - 1    if fd_max == -1 or fd_max > fd_top:        fd_max = fd_top    for fd in range(fd_min, fd_max+1):        try:            os.close(fd)        except OSError:            passdef close_files_with_procfs(fd_min=3, fd_max=-1):    for nm in os.listdir("/proc/self/fd"):        if nm.startswith('.'):            continue        fd = int(nm)        if fd >= fd_min and (fd_max == -1 or fd < fd_max):            try:                os.close(fd)            except OSError:                passdef timereps(reps, func):    from time import time    start = time()    for i in range(0, reps):        func()    end = time()    return (end - start) / repsprint "close_files: %f" % timereps(100, lambda: close_files())print "close_files_exhaustively: %f" % timereps(100, lambda: close_files_exhaustively())print "close_files_with_procfs: %f" % timereps(1000, lambda: close_files_with_procfs())

On my system:

$ python ./close_fds.py close_files: 0.000094close_files_exhaustively: 0.010151close_files_with_procfs: 0.000039