Fix garbage collection of Notifier

This uses a weak reference to the notifier in _SysProcessEvent and adds
a `__del__` method for Notifier.

This prevents pyinotify from leaking inotify file descriptors
(instances) and its watches.

Fixes seb-m#95

I have used the following script to test it:

    from __future__ import print_function

    import gc
    import os

    from pyinotify import Notifier, WatchManager

    def has_inotify_fds():
        "Does the current process have inotify fds?"
        r = 0
        for x in os.walk('/proc/{}/fd'.format(os.getpid())):
            for y in x[2]:
                path = os.path.join(x[0], y)
                if os.path.exists(path):
                    if 'inotify' in os.path.join(os.readlink(path)):
                        r += 1
        return r

    gc.disable()

    wm = WatchManager()
    n = Notifier(wm)
    assert has_inotify_fds() == 1

    # Stopping multiple times should work:
    n.stop()
    assert has_inotify_fds() == 0
    n.stop()

    gc.collect()
    # XXX: needs a new WatchManager, because the previous fd gets closed by stop!
    wm = WatchManager()
    n = Notifier(wm)
    assert has_inotify_fds() == 1

    # Collect anything.
    gc.collect()
    assert n in gc.get_objects()

    n = None
    assert gc.garbage == []
    assert not any(isinstance(x, Notifier) for x in gc.garbage)
    assert not any(isinstance(x, Notifier) for x in gc.get_objects())

    assert has_inotify_fds() == 0

python2/pyinotify.py

@@ -69,6 +69,7 @@ def __init__(self, version):
 import re
 import asyncore
 import subprocess
+import weakref
 
 try:
     from functools import reduce
@@ -708,7 +709,7 @@ def __init__(self, wm, notifier):
         @type notifier: Notifier instance
         """
         self._watch_manager = wm  # watch manager
-        self._notifier = notifier  # notifier
+        self._notifier = weakref.ref(notifier)  # notifier
         self._mv_cookie = {}  # {cookie(int): (src_path(str), date), ...}
         self._mv = {}  # {src_path(str): (dst_path(str), date), ...}
 
@@ -766,7 +767,7 @@ def process_IN_CREATE(self, raw_event):
                                 # This path should not be taken.
                                 continue
                             rawevent = _RawEvent(created_dir_wd, flags, 0, name)
-                            self._notifier.append_event(rawevent)
+                            self._notifier().append_event(rawevent)
                     except OSError, err:
                         msg = "process_IN_CREATE, invalid directory %s: %s"
                         log.debug(msg % (created_dir, str(err)))
@@ -1191,6 +1192,9 @@ def __init__(self, watch_manager, default_proc_fun=None, read_freq=0,
         # set of str(raw_event), only used when coalesce option is True
         self._eventset = set()
 
+    def __del__(self):
+        self.stop()
+
     def append_event(self, event):
         """
         Append a raw event to the event queue.

python3/pyinotify.py

@@ -72,6 +72,7 @@ def __init__(self, version):
 import glob
 import locale
 import subprocess
+import weakref
 
 try:
     from functools import reduce
@@ -698,7 +699,7 @@ def __init__(self, wm, notifier):
         @type notifier: Notifier instance
         """
         self._watch_manager = wm  # watch manager
-        self._notifier = notifier  # notifier
+        self._notifier = weakref.ref(notifier)  # notifier
         self._mv_cookie = {}  # {cookie(int): (src_path(str), date), ...}
         self._mv = {}  # {src_path(str): (dst_path(str), date), ...}
 
@@ -756,7 +757,7 @@ def process_IN_CREATE(self, raw_event):
                                 # This path should not be taken.
                                 continue
                             rawevent = _RawEvent(created_dir_wd, flags, 0, name)
-                            self._notifier.append_event(rawevent)
+                            self._notifier().append_event(rawevent)
                     except OSError as err:
                         msg = "process_IN_CREATE, invalid directory: %s"
                         log.debug(msg % str(err))
@@ -1181,6 +1182,9 @@ def __init__(self, watch_manager, default_proc_fun=None, read_freq=0,
         # set of str(raw_event), only used when coalesce option is True
         self._eventset = set()
 
+    def __del__(self):
+        self.stop()
+
     def append_event(self, event):
         """
         Append a raw event to the event queue.