Hobu, Inc.

I do most of my development on OS X, but I do have parallels instances for both Ubuntu and Windows. One thing I really miss on OS X and Windows is valgrind. It is the savior of dumb C/C++ programmers like myself everywhere. Apple ships a couple of tools that are close to approaching the utility of valgrind.

• Chris Hanson’s nice description of how to use the leaks command on OS X.
• ‘man malloc’ on OS X describes a number of environment variables you can use for malloc tracing on OS X.

Still not as good as valgrind, but close enough for a lot of cases…

Mac OSX (and all? BSDs) provide a kernel event notification mechanism called kqueue. Other operating systems provide a similar sort of notification system, but OSX’s is the only one I am interested at this time. I did find a rather interesting cross-platform notification library called libevent-python, which attempts to provide a unified API, but it appears to be geared toward network communication and not toward file system notification.

Here’s a BSD-licensed class that can be used to watch a directory. It requires the PyKQueue from hpio.

import osimport kqueueimport sets

class DirectoryChangedException(Exception):    pass

class Watch(object):    def __init__(self, directory):        self.directory = directory        self.dirfd = os.open(self.directory, os.O_RDONLY)        self.filter = kqueue.EV_ADD|kqueue.EV_CLEAR|kqueue.EV_ENABLE        self.event = kqueue.Event(self.dirfd,                                  kqueue.EVFILT_VNODE,                                  self.filter,                                  fflags=kqueue.NOTE_WRITE|\                                         kqueue.NOTE_DELETE|\                                         kqueue.NOTE_EXTEND,                                  data=self.dirfd)        self.kq = kqueue.kqueue()

    def watch(self):        self.files = sets.Set(os.listdir(self.directory))        self.adds = None; self.deletes=None; self.changed=None         while 1:            events = kqueue.kevent(self.kq, [self.event], 10, None)            if events:                new_files = sets.Set(os.listdir(self.directory))                self.deletes = list(self.files.difference(new_files))                self.adds = list(new_files.difference(self.files))                self.files = new_files                raise DirectoryChangedException, \                      “Directory %s changed…” % self.directory    def __del__(self):        os.close(self.dirfd)

One way to use it is as so:

import watchw = watch.Watch('/Users/hobu/foo')

while 1:    try:        w.watch()    except watch.DirectoryChangedException:        adds = w.adds        deletes = w.deletes        print "added files: ", adds        print "deleted files: ", deletes