inotify: server: refactor updatestatus()

* Instead of one entry point, use two entry points, updatefile()
  and deletefile(), both internally calling the helper function _updatestatus
* Do not rely on TypeError to detect the type of oldstatus: use isinstance
* The call updatestatus(wpath, None) in deleted() was a bit particular:
  because no osstat and no newstatus was given, the newstatus was determined
  using the data stored internally. To replace this exact behavior with the
  new code, one would use:
    root, fn = self.split(wpath)
    d = self.dir(self.tree, root)
    self.filedeleted(wpath, d.get(fn))
  This, however, duplicates code with _updatestatus(), which led us to an
  interesting question: why are we basing ourselves on repowatcher data to
  update the status, where everywhere else, we are comparing against dirsate?
  There is no reason to do this, which is why the new code is:
    self.filedeleted(wpath, self.repo.dirstate[wpath])
  Incidentally, after this, the test for issue1371 passes again.

hgext/inotify/server.py

@@ -1,776 +1,791 b''
 # server.py - inotify status server
 #
 # Copyright 2006, 2007, 2008 Bryan O'Sullivan <[e-mail]>
 # Copyright 2007, 2008 Brendan Cully <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2, incorporated herein by reference.
 
 from mercurial.i18n import _
 from mercurial import osutil, util
 import common
 import errno, os, select, socket, stat, struct, sys, tempfile, time
 
 try:
     import linux as inotify
     from linux import watcher
 except ImportError:
     raise
 
 class AlreadyStartedException(Exception): pass
 
 def join(a, b):
     if a:
         if a[-1] == '/':
             return a + b
         return a + '/' + b
     return b
 
 walk_ignored_errors = (errno.ENOENT, errno.ENAMETOOLONG)
 
 def walkrepodirs(repo):
     '''Iterate over all subdirectories of this repo.
     Exclude the .hg directory, any nested repos, and ignored dirs.'''
     rootslash = repo.root + os.sep
 
     def walkit(dirname, top):
         fullpath = rootslash + dirname
         try:
             for name, kind in osutil.listdir(fullpath):
                 if kind == stat.S_IFDIR:
                     if name == '.hg':
                         if not top:
                             return
                     else:
                         d = join(dirname, name)
                         if repo.dirstate._ignore(d):
                             continue
                         for subdir in walkit(d, False):
                             yield subdir
         except OSError, err:
             if err.errno not in walk_ignored_errors:
                 raise
         yield fullpath
 
     return walkit('', True)
 
 def walk(repo, root):
     '''Like os.walk, but only yields regular files.'''
 
     # This function is critical to performance during startup.
 
     rootslash = repo.root + os.sep
 
     def walkit(root, reporoot):
         files, dirs = [], []
 
         try:
             fullpath = rootslash + root
             for name, kind in osutil.listdir(fullpath):
                 if kind == stat.S_IFDIR:
                     if name == '.hg':
                         if not reporoot:
                             return
                     else:
                         dirs.append(name)
                         path = join(root, name)
                         if repo.dirstate._ignore(path):
                             continue
                         for result in walkit(path, False):
                             yield result
                 elif kind in (stat.S_IFREG, stat.S_IFLNK):
                     files.append(name)
             yield fullpath, dirs, files
 
         except OSError, err:
             if err.errno not in walk_ignored_errors:
                 raise
 
     return walkit(root, root == '')
 
 def _explain_watch_limit(ui, repo, count):
     path = '/proc/sys/fs/inotify/max_user_watches'
     try:
         limit = int(file(path).read())
     except IOError, err:
         if err.errno != errno.ENOENT:
             raise
         raise util.Abort(_('this system does not seem to '
                            'support inotify'))
     ui.warn(_('*** the current per-user limit on the number '
               'of inotify watches is %s\n') % limit)
     ui.warn(_('*** this limit is too low to watch every '
               'directory in this repository\n'))
     ui.warn(_('*** counting directories: '))
     ndirs = len(list(walkrepodirs(repo)))
     ui.warn(_('found %d\n') % ndirs)
     newlimit = min(limit, 1024)
     while newlimit < ((limit + ndirs) * 1.1):
         newlimit *= 2
     ui.warn(_('*** to raise the limit from %d to %d (run as root):\n') %
             (limit, newlimit))
     ui.warn(_('***  echo %d > %s\n') % (newlimit, path))
     raise util.Abort(_('cannot watch %s until inotify watch limit is raised')
                      % repo.root)
 
 class repowatcher(object):
     poll_events = select.POLLIN
     statuskeys = 'almr!?'
     mask = (
         inotify.IN_ATTRIB |
         inotify.IN_CREATE |
         inotify.IN_DELETE |
         inotify.IN_DELETE_SELF |
         inotify.IN_MODIFY |
         inotify.IN_MOVED_FROM |
         inotify.IN_MOVED_TO |
         inotify.IN_MOVE_SELF |
         inotify.IN_ONLYDIR |
         inotify.IN_UNMOUNT |
         0)
 
     def __init__(self, ui, repo, master):
         self.ui = ui
         self.repo = repo
         self.wprefix = self.repo.wjoin('')
         self.timeout = None
         self.master = master
         try:
             self.watcher = watcher.watcher()
         except OSError, err:
             raise util.Abort(_('inotify service not available: %s') %
                              err.strerror)
         self.threshold = watcher.threshold(self.watcher)
         self.registered = True
         self.fileno = self.watcher.fileno
 
         self.tree = {}
         self.statcache = {}
         self.statustrees = dict([(s, {}) for s in self.statuskeys])
 
         self.watches = 0
         self.last_event = None
 
         self.eventq = {}
         self.deferred = 0
 
         self.ds_info = self.dirstate_info()
         self.scan()
 
     def event_time(self):
         last = self.last_event
         now = time.time()
         self.last_event = now
 
         if last is None:
             return 'start'
         delta = now - last
         if delta < 5:
             return '+%.3f' % delta
         if delta < 50:
             return '+%.2f' % delta
         return '+%.1f' % delta
 
     def dirstate_info(self):
         try:
             st = os.lstat(self.repo.join('dirstate'))
             return st.st_mtime, st.st_ino
         except OSError, err:
             if err.errno != errno.ENOENT:
                 raise
             return 0, 0
 
     def add_watch(self, path, mask):
         if not path:
             return
         if self.watcher.path(path) is None:
             if self.ui.debugflag:
                 self.ui.note(_('watching %r\n') % path[len(self.wprefix):])
             try:
                 self.watcher.add(path, mask)
                 self.watches += 1
             except OSError, err:
                 if err.errno in (errno.ENOENT, errno.ENOTDIR):
                     return
                 if err.errno != errno.ENOSPC:
                     raise
                 _explain_watch_limit(self.ui, self.repo, self.watches)
 
     def setup(self):
         self.ui.note(_('watching directories under %r\n') % self.repo.root)
         self.add_watch(self.repo.path, inotify.IN_DELETE)
         self.check_dirstate()
 
     def wpath(self, evt):
         path = evt.fullpath
         if path == self.repo.root:
             return ''
         if path.startswith(self.wprefix):
             return path[len(self.wprefix):]
         raise 'wtf? ' + path
 
     def dir(self, tree, path):
         if path:
             for name in path.split('/'):
                 tree = tree.setdefault(name, {})
         return tree
 
     def lookup(self, path, tree):
         if path:
             try:
                 for name in path.split('/'):
                     tree = tree[name]
             except KeyError:
                 return 'x'
             except TypeError:
                 return 'd'
         return tree
 
     def split(self, path):
         c = path.rfind('/')
         if c == -1:
             return '', path
         return path[:c], path[c+1:]
 
     def filestatus(self, fn, st):
         try:
             type_, mode, size, time = self.repo.dirstate._map[fn][:4]
         except KeyError:
             type_ = '?'
         if type_ == 'n':
             st_mode, st_size, st_mtime = st
             if size == -1:
                 return 'l'
             if size and (size != st_size or (mode ^ st_mode) & 0100):
                 return 'm'
             if time != int(st_mtime):
                 return 'l'
             return 'n'
         if type_ == '?' and self.repo.dirstate._ignore(fn):
             return 'i'
         return type_
 
-    def updatestatus(self, wfn, osstat=None, newstatus=None):
+    def updatefile(self, wfn, osstat):
+        '''
+        update the file entry of an existing file.
+
+        osstat: (mode, size, time) tuple, as returned by os.lstat(wfn)
+        '''
+
+        self._updatestatus(wfn, self.filestatus(wfn, osstat))
+
+    def deletefile(self, wfn, oldstatus):
+        '''
+        update the entry of a file which has been deleted.
+
+        oldstatus: char in statuskeys, status of the file before deletion
+        '''
+        if oldstatus == 'r':
+            newstatus = 'r'
+        elif oldstatus in 'almn':
+            newstatus = '!'
+        else:
+            newstatus = None
+
+        self.statcache.pop(wfn, None)
+        self._updatestatus(wfn, newstatus)
+
+    def _updatestatus(self, wfn, newstatus):
         '''
         Update the stored status of a file or directory.
 
-        osstat: (mode, size, time) tuple, as returned by os.lstat(wfn)
-
-        newstatus: char in statuskeys, new status to apply.
+        newstatus: - char in (statuskeys + 'ni'), new status to apply.
+                   - or None, to stop tracking wfn
         '''
-        if osstat:
-            newstatus = self.filestatus(wfn, osstat)
-        else:
-            self.statcache.pop(wfn, None)
         root, fn = self.split(wfn)
         d = self.dir(self.tree, root)
+
         oldstatus = d.get(fn)
-        isdir = False
-        if oldstatus:
-            try:
-                if not newstatus:
-                    if oldstatus in 'almn':
-                        newstatus = '!'
-                    elif oldstatus == 'r':
-                        newstatus = 'r'
-            except TypeError:
-                # oldstatus may be a dict left behind by a deleted
-                # directory
-                isdir = True
-            else:
-                if oldstatus in self.statuskeys and oldstatus != newstatus:
-                    del self.dir(self.statustrees[oldstatus], root)[fn]
+        # oldstatus can be either:
+        # - None : fn is new
+        # - a char in statuskeys: fn is a (tracked) file
+        # - a dict: fn is a directory
+        isdir = isinstance(oldstatus, dict)
+
         if self.ui.debugflag and oldstatus != newstatus:
             if isdir:
                 self.ui.note(_('status: %r dir(%d) -> %s\n') %
                              (wfn, len(oldstatus), newstatus))
             else:
                 self.ui.note(_('status: %r %s -> %s\n') %
                              (wfn, oldstatus, newstatus))
         if not isdir:
+            if oldstatus and oldstatus in self.statuskeys \
+                and oldstatus != newstatus:
+                del self.dir(self.statustrees[oldstatus], root)[fn]
             if newstatus and newstatus != 'i':
                 d[fn] = newstatus
                 if newstatus in self.statuskeys:
                     dd = self.dir(self.statustrees[newstatus], root)
                     if oldstatus != newstatus or fn not in dd:
                         dd[fn] = newstatus
             else:
                 d.pop(fn, None)
         elif not newstatus:
             # a directory is being removed, check its contents
             for subfile, b in oldstatus.copy().iteritems():
-                self.updatestatus(wfn + '/' + subfile, None)
+                self._updatestatus(wfn + '/' + subfile, None)
 
 
     def check_deleted(self, key):
         # Files that had been deleted but were present in the dirstate
         # may have vanished from the dirstate; we must clean them up.
         nuke = []
         for wfn, ignore in self.walk(key, self.statustrees[key]):
             if wfn not in self.repo.dirstate:
                 nuke.append(wfn)
         for wfn in nuke:
             root, fn = self.split(wfn)
             del self.dir(self.statustrees[key], root)[fn]
             del self.dir(self.tree, root)[fn]
 
     def scan(self, topdir=''):
         self.handle_timeout()
         ds = self.repo.dirstate._map.copy()
         self.add_watch(join(self.repo.root, topdir), self.mask)
         for root, dirs, files in walk(self.repo, topdir):
             for d in dirs:
                 self.add_watch(join(root, d), self.mask)
             wroot = root[len(self.wprefix):]
             d = self.dir(self.tree, wroot)
             for fn in files:
                 wfn = join(wroot, fn)
-                self.updatestatus(wfn, self.getstat(wfn))
+                self.updatefile(wfn, self.getstat(wfn))
                 ds.pop(wfn, None)
         wtopdir = topdir
         if wtopdir and wtopdir[-1] != '/':
             wtopdir += '/'
         for wfn, state in ds.iteritems():
             if not wfn.startswith(wtopdir):
                 continue
             try:
                 st = self.stat(wfn)
             except OSError:
                 status = state[0]
-                self.updatestatus(wfn, None, newstatus=status)
+                self.deletefile(wfn, status)
             else:
-                self.updatestatus(wfn, st)
+                self.updatefile(wfn, st)
         self.check_deleted('!')
         self.check_deleted('r')
 
     def check_dirstate(self):
         ds_info = self.dirstate_info()
         if ds_info == self.ds_info:
             return
         self.ds_info = ds_info
         if not self.ui.debugflag:
             self.last_event = None
         self.ui.note(_('%s dirstate reload\n') % self.event_time())
         self.repo.dirstate.invalidate()
         self.scan()
         self.ui.note(_('%s end dirstate reload\n') % self.event_time())
 
     def walk(self, states, tree, prefix=''):
         # This is the "inner loop" when talking to the client.
 
         for name, val in tree.iteritems():
             path = join(prefix, name)
             try:
                 if val in states:
                     yield path, val
             except TypeError:
                 for p in self.walk(states, val, path):
                     yield p
 
     def update_hgignore(self):
         # An update of the ignore file can potentially change the
         # states of all unknown and ignored files.
 
         # XXX If the user has other ignore files outside the repo, or
         # changes their list of ignore files at run time, we'll
         # potentially never see changes to them.  We could get the
         # client to report to us what ignore data they're using.
         # But it's easier to do nothing than to open that can of
         # worms.
 
         if '_ignore' in self.repo.dirstate.__dict__:
             delattr(self.repo.dirstate, '_ignore')
             self.ui.note(_('rescanning due to .hgignore change\n'))
             self.scan()
 
     def getstat(self, wpath):
         try:
             return self.statcache[wpath]
         except KeyError:
             try:
                 return self.stat(wpath)
             except OSError, err:
                 if err.errno != errno.ENOENT:
                     raise
 
     def stat(self, wpath):
         try:
             st = os.lstat(join(self.wprefix, wpath))
             ret = st.st_mode, st.st_size, st.st_mtime
             self.statcache[wpath] = ret
             return ret
         except OSError:
             self.statcache.pop(wpath, None)
             raise
 
     def created(self, wpath):
         if wpath == '.hgignore':
             self.update_hgignore()
         try:
             st = self.stat(wpath)
             if stat.S_ISREG(st[0]):
-                self.updatestatus(wpath, st)
+                self.updatefile(wpath, st)
         except OSError:
             pass
 
     def modified(self, wpath):
         if wpath == '.hgignore':
             self.update_hgignore()
         try:
             st = self.stat(wpath)
             if stat.S_ISREG(st[0]):
                 if self.repo.dirstate[wpath] in 'lmn':
-                    self.updatestatus(wpath, st)
+                    self.updatefile(wpath, st)
         except OSError:
             pass
 
     def deleted(self, wpath):
         if wpath == '.hgignore':
             self.update_hgignore()
         elif wpath.startswith('.hg/'):
             if wpath == '.hg/wlock':
                 self.check_dirstate()
             return
 
-        self.updatestatus(wpath, None)
+        self.deletefile(wpath, self.repo.dirstate[wpath])
 
     def schedule_work(self, wpath, evt):
         prev = self.eventq.setdefault(wpath, [])
         try:
             if prev and evt == 'm' and prev[-1] in 'cm':
                 return
             self.eventq[wpath].append(evt)
         finally:
             self.deferred += 1
             self.timeout = 250
 
     def deferred_event(self, wpath, evt):
         if evt == 'c':
             self.created(wpath)
         elif evt == 'm':
             self.modified(wpath)
         elif evt == 'd':
             self.deleted(wpath)
 
     def process_create(self, wpath, evt):
         if self.ui.debugflag:
             self.ui.note(_('%s event: created %s\n') %
                          (self.event_time(), wpath))
 
         if evt.mask & inotify.IN_ISDIR:
             self.scan(wpath)
         else:
             self.schedule_work(wpath, 'c')
 
     def process_delete(self, wpath, evt):
         if self.ui.debugflag:
             self.ui.note(_('%s event: deleted %s\n') %
                          (self.event_time(), wpath))
 
         if evt.mask & inotify.IN_ISDIR:
             self.scan(wpath)
         self.schedule_work(wpath, 'd')
 
     def process_modify(self, wpath, evt):
         if self.ui.debugflag:
             self.ui.note(_('%s event: modified %s\n') %
                          (self.event_time(), wpath))
 
         if not (evt.mask & inotify.IN_ISDIR):
             self.schedule_work(wpath, 'm')
 
     def process_unmount(self, evt):
         self.ui.warn(_('filesystem containing %s was unmounted\n') %
                      evt.fullpath)
         sys.exit(0)
 
     def handle_event(self, fd, event):
         if self.ui.debugflag:
             self.ui.note(_('%s readable: %d bytes\n') %
                          (self.event_time(), self.threshold.readable()))
         if not self.threshold():
             if self.registered:
                 if self.ui.debugflag:
                     self.ui.note(_('%s below threshold - unhooking\n') %
                                  (self.event_time()))
                 self.master.poll.unregister(fd)
                 self.registered = False
                 self.timeout = 250
         else:
             self.read_events()
 
     def read_events(self, bufsize=None):
         events = self.watcher.read(bufsize)
         if self.ui.debugflag:
             self.ui.note(_('%s reading %d events\n') %
                          (self.event_time(), len(events)))
         for evt in events:
             wpath = self.wpath(evt)
             if evt.mask & inotify.IN_UNMOUNT:
                 self.process_unmount(wpath, evt)
             elif evt.mask & (inotify.IN_MODIFY | inotify.IN_ATTRIB):
                 self.process_modify(wpath, evt)
             elif evt.mask & (inotify.IN_DELETE | inotify.IN_DELETE_SELF |
                              inotify.IN_MOVED_FROM):
                 self.process_delete(wpath, evt)
             elif evt.mask & (inotify.IN_CREATE | inotify.IN_MOVED_TO):
                 self.process_create(wpath, evt)
 
     def handle_timeout(self):
         if not self.registered:
             if self.ui.debugflag:
                 self.ui.note(_('%s hooking back up with %d bytes readable\n') %
                              (self.event_time(), self.threshold.readable()))
             self.read_events(0)
             self.master.poll.register(self, select.POLLIN)
             self.registered = True
 
         if self.eventq:
             if self.ui.debugflag:
                 self.ui.note(_('%s processing %d deferred events as %d\n') %
                              (self.event_time(), self.deferred,
                               len(self.eventq)))
             for wpath, evts in sorted(self.eventq.iteritems()):
                 for evt in evts:
                     self.deferred_event(wpath, evt)
             self.eventq.clear()
             self.deferred = 0
         self.timeout = None
 
     def shutdown(self):
         self.watcher.close()
 
     def debug(self):
         """
         Returns a sorted list of relatives paths currently watched,
         for debugging purposes.
         """
         return sorted(tuple[0][len(self.wprefix):] for tuple in self.watcher)
 
 class server(object):
     poll_events = select.POLLIN
 
     def __init__(self, ui, repo, repowatcher, timeout):
         self.ui = ui
         self.repo = repo
         self.repowatcher = repowatcher
         self.timeout = timeout
         self.sock = socket.socket(socket.AF_UNIX)
         self.sockpath = self.repo.join('inotify.sock')
         self.realsockpath = None
         try:
             self.sock.bind(self.sockpath)
         except socket.error, err:
             if err[0] == errno.EADDRINUSE:
                 raise AlreadyStartedException(_('could not start server: %s')
                                               % err[1])
             if err[0] == "AF_UNIX path too long":
                 tempdir = tempfile.mkdtemp(prefix="hg-inotify-")
                 self.realsockpath = os.path.join(tempdir, "inotify.sock")
                 try:
                     self.sock.bind(self.realsockpath)
                     os.symlink(self.realsockpath, self.sockpath)
                 except (OSError, socket.error), inst:
                     try:
                         os.unlink(self.realsockpath)
                     except:
                         pass
                     os.rmdir(tempdir)
                     if inst.errno == errno.EEXIST:
                         raise AlreadyStartedException(_('could not start server: %s')
                                                       % inst.strerror)
                     raise
             else:
                 raise
         self.sock.listen(5)
         self.fileno = self.sock.fileno
 
     def handle_timeout(self):
         pass
 
     def answer_stat_query(self, cs):
         names = cs.read().split('\0')
 
         states = names.pop()
 
         self.ui.note(_('answering query for %r\n') % states)
 
         if self.repowatcher.timeout:
             # We got a query while a rescan is pending.  Make sure we
             # rescan before responding, or we could give back a wrong
             # answer.
             self.repowatcher.handle_timeout()
 
         if not names:
             def genresult(states, tree):
                 for fn, state in self.repowatcher.walk(states, tree):
                     yield fn
         else:
             def genresult(states, tree):
                 for fn in names:
                     l = self.repowatcher.lookup(fn, tree)
                     try:
                         if l in states:
                             yield fn
                     except TypeError:
                         for f, s in self.repowatcher.walk(states, l, fn):
                             yield f
 
         return ['\0'.join(r) for r in [
             genresult('l', self.repowatcher.statustrees['l']),
             genresult('m', self.repowatcher.statustrees['m']),
             genresult('a', self.repowatcher.statustrees['a']),
             genresult('r', self.repowatcher.statustrees['r']),
             genresult('!', self.repowatcher.statustrees['!']),
             '?' in states
                 and genresult('?', self.repowatcher.statustrees['?'])
                 or [],
             [],
             'c' in states and genresult('n', self.repowatcher.tree) or [],
             ]]
 
     def answer_dbug_query(self):
         return ['\0'.join(self.repowatcher.debug())]
 
     def handle_event(self, fd, event):
         sock, addr = self.sock.accept()
 
         cs = common.recvcs(sock)
         version = ord(cs.read(1))
 
         if version != common.version:
             self.ui.warn(_('received query from incompatible client '
                            'version %d\n') % version)
             return
 
         type = cs.read(4)
 
         if type == 'STAT':
             results = self.answer_stat_query(cs)
         elif type == 'DBUG':
             results = self.answer_dbug_query()
         else:
             self.ui.warn(_('unrecognized query type: %s\n') % type)
             return
 
         try:
             try:
                 v = chr(common.version)
 
                 sock.sendall(v + type + struct.pack(common.resphdrfmts[type],
                                             *map(len, results)))
                 sock.sendall(''.join(results))
             finally:
                 sock.shutdown(socket.SHUT_WR)
         except socket.error, err:
             if err[0] != errno.EPIPE:
                 raise
 
     def shutdown(self):
         self.sock.close()
         try:
             os.unlink(self.sockpath)
             if self.realsockpath:
                 os.unlink(self.realsockpath)
                 os.rmdir(os.path.dirname(self.realsockpath))
         except OSError, err:
             if err.errno != errno.ENOENT:
                 raise
 
 class master(object):
     def __init__(self, ui, repo, timeout=None):
         self.ui = ui
         self.repo = repo
         self.poll = select.poll()
         self.repowatcher = repowatcher(ui, repo, self)
         self.server = server(ui, repo, self.repowatcher, timeout)
         self.table = {}
         for obj in (self.repowatcher, self.server):
             fd = obj.fileno()
             self.table[fd] = obj
             self.poll.register(fd, obj.poll_events)
 
     def register(self, fd, mask):
         self.poll.register(fd, mask)
 
     def shutdown(self):
         for obj in self.table.itervalues():
             obj.shutdown()
 
     def run(self):
         self.repowatcher.setup()
         self.ui.note(_('finished setup\n'))
         if os.getenv('TIME_STARTUP'):
             sys.exit(0)
         while True:
             timeout = None
             timeobj = None
             for obj in self.table.itervalues():
                 if obj.timeout is not None and (timeout is None or obj.timeout < timeout):
                     timeout, timeobj = obj.timeout, obj
             try:
                 if self.ui.debugflag:
                     if timeout is None:
                         self.ui.note(_('polling: no timeout\n'))
                     else:
                         self.ui.note(_('polling: %sms timeout\n') % timeout)
                 events = self.poll.poll(timeout)
             except select.error, err:
                 if err[0] == errno.EINTR:
                     continue
                 raise
             if events:
                 for fd, event in events:
                     self.table[fd].handle_event(fd, event)
             elif timeobj:
                 timeobj.handle_timeout()
 
 def start(ui, repo):
     def closefds(ignore):
         # (from python bug #1177468)
         # close all inherited file descriptors
         # Python 2.4.1 and later use /dev/urandom to seed the random module's RNG
         # a file descriptor is kept internally as os._urandomfd (created on demand
         # the first time os.urandom() is called), and should not be closed
         try:
             os.urandom(4)
             urandom_fd = getattr(os, '_urandomfd', None)
         except AttributeError:
             urandom_fd = None
         ignore.append(urandom_fd)
         for fd in range(3, 256):
             if fd in ignore:
                 continue
             try:
                 os.close(fd)
             except OSError:
                 pass
 
     m = master(ui, repo)
     sys.stdout.flush()
     sys.stderr.flush()
 
     pid = os.fork()
     if pid:
         return pid
 
     closefds([m.server.fileno(), m.repowatcher.fileno()])
     os.setsid()
 
     fd = os.open('/dev/null', os.O_RDONLY)
     os.dup2(fd, 0)
     if fd > 0:
         os.close(fd)
 
     fd = os.open(ui.config('inotify', 'log', '/dev/null'),
                  os.O_RDWR | os.O_CREAT | os.O_TRUNC)
     os.dup2(fd, 1)
     os.dup2(fd, 2)
     if fd > 2:
         os.close(fd)
 
     try:
         m.run()
     finally:
         m.shutdown()
         os._exit(0)