--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/hgext/fsmonitor/state.py	Thu Mar 03 14:29:19 2016 +0000
@@ -0,0 +1,115 @@
+# state.py - fsmonitor persistent state
+#
+# Copyright 2013-2016 Facebook, Inc.
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+from __future__ import absolute_import
+
+import errno
+import os
+import socket
+import struct
+
+from mercurial import pathutil
+from mercurial.i18n import _
+
+_version = 4
+_versionformat = ">I"
+
+class state(object):
+    def __init__(self, repo):
+        self._opener = repo.opener
+        self._ui = repo.ui
+        self._rootdir = pathutil.normasprefix(repo.root)
+        self._lastclock = None
+
+        self.mode = self._ui.config('fsmonitor', 'mode', default='on')
+        self.walk_on_invalidate = self._ui.configbool(
+            'fsmonitor', 'walk_on_invalidate', False)
+        self.timeout = float(self._ui.config(
+            'fsmonitor', 'timeout', default='2'))
+
+    def get(self):
+        try:
+            file = self._opener('fsmonitor.state', 'rb')
+        except IOError as inst:
+            if inst.errno != errno.ENOENT:
+                raise
+            return None, None, None
+
+        versionbytes = file.read(4)
+        if len(versionbytes) < 4:
+            self._ui.log(
+                'fsmonitor', 'fsmonitor: state file only has %d bytes, '
+                'nuking state\n' % len(versionbytes))
+            self.invalidate()
+            return None, None, None
+        try:
+            diskversion = struct.unpack(_versionformat, versionbytes)[0]
+            if diskversion != _version:
+                # different version, nuke state and start over
+                self._ui.log(
+                    'fsmonitor', 'fsmonitor: version switch from %d to '
+                    '%d, nuking state\n' % (diskversion, _version))
+                self.invalidate()
+                return None, None, None
+
+            state = file.read().split('\0')
+            # state = hostname\0clock\0ignorehash\0 + list of files, each
+            # followed by a \0
+            diskhostname = state[0]
+            hostname = socket.gethostname()
+            if diskhostname != hostname:
+                # file got moved to a different host
+                self._ui.log('fsmonitor', 'fsmonitor: stored hostname "%s" '
+                             'different from current "%s", nuking state\n' %
+                             (diskhostname, hostname))
+                self.invalidate()
+                return None, None, None
+
+            clock = state[1]
+            ignorehash = state[2]
+            # discard the value after the last \0
+            notefiles = state[3:-1]
+
+        finally:
+            file.close()
+
+        return clock, ignorehash, notefiles
+
+    def set(self, clock, ignorehash, notefiles):
+        if clock is None:
+            self.invalidate()
+            return
+
+        try:
+            file = self._opener('fsmonitor.state', 'wb')
+        except (IOError, OSError):
+            self._ui.warn(_("warning: unable to write out fsmonitor state\n"))
+            return
+
+        try:
+            file.write(struct.pack(_versionformat, _version))
+            file.write(socket.gethostname() + '\0')
+            file.write(clock + '\0')
+            file.write(ignorehash + '\0')
+            if notefiles:
+                file.write('\0'.join(notefiles))
+                file.write('\0')
+        finally:
+            file.close()
+
+    def invalidate(self):
+        try:
+            os.unlink(os.path.join(self._rootdir, '.hg', 'fsmonitor.state'))
+        except OSError as inst:
+            if inst.errno != errno.ENOENT:
+                raise
+
+    def setlastclock(self, clock):
+        self._lastclock = clock
+
+    def getlastclock(self):
+        return self._lastclock