    #!/usr/bin/env python

    """AutoReloadingAppServer

    This module defines `AutoReloadingAppServer`, a replacement for `AppServer`
    that adds a file-monitoring and restarting to the AppServer. Used mostly like:

        from AutoReloadingAppServer import AutoReloadingAppServer as AppServer

    If `UseImportSpy` is set to False in AppServer.config, or FAM support is
    not available, this requires regular polling. The interval for the polling
    in seconds can be set with `AutoReloadPollInterval` in AppServer.config.

    """

    import select, errno
    from threading import Thread

    from Common import *
    from AppServer import AppServer

    defaultConfig = {
        'AutoReload': False,
        'AutoReloadPollInterval': 1, # in seconds
        'UseImportSpy': True,
        'UseFAMModules': 'gamin _fam',
    }

    def getFAM(modules):
        """Get FAM object based on the modules specified.

        Currently supported are
        python-gamin (gamin): http://www.gnome.org/~veillard/gamin/
        python-fam (_fam): http://python-fam.sourceforge.net

        """
        for module in modules:
            global fam # for Python < 2.2
            try:
                fam = __import__(module)
            except ImportError:
                fam = None
            if not fam:
                continue
            if hasattr(fam, 'GAM_CONNECT') and hasattr(
                    fam, 'WatchMonitor') and hasattr(fam, 'GAMChanged'):

                class FAM:
                    """Simple File Alteration Monitor based on python-gamin"""

                    def name(self):
                        return "python-gamin"

                    def __init__(self):
                        """Initialize and start monitoring."""
                        self._mon = fam.WatchMonitor()
                        self._watchlist = []

                    def close(self):
                        """Stop monitoring and close."""
                        for filepath in self._watchlist:
                            self._mon.stop_watch(filepath)
                        self._mon.disconnect()

                    def fd(self):
                        """Get file descriptor for monitor."""
                        return self._mon.get_fd()

                    def monitorFile(self, filepath):
                        """Monitor one file."""
                        self._mon.watch_file(filepath, self.callback)
                        self._watchlist.append(filepath)

                    def pending(self):
                        """Check whether an event is pending."""
                        return self._mon.event_pending()

                    def nextFile(self):
                        """Get next file and return whether it has changed."""
                        self._mon.handle_one_event()
                        return self._changed, self._filepath

                    def callback(self, filepath, event):
                        """Callback function for WatchMonitor."""
                        self._filepath = filepath
                        self._changed = {fam.GAMChanged: 'changed',
                            fam.GAMCreated: 'created', fam.GAMMoved: 'moved',
                            fam.GAMDeleted: 'deleted'}.get(event)

                break
            elif hasattr(fam, 'FAMConnection') and hasattr(
                    fam, 'open') and hasattr(fam, 'Changed'):

                class FAM:
                    """Simple File Alteration Monitor based on python-fam"""

                    def name(self):
                        return "python-fam"

                    def __init__(self):
                        """Initialize and start monitoring."""
                        self._fc = fam.open()
                        self._requests = []

                    def close(self):
                        """Stop monitoring and close."""
                        for request in self._requests:
                            request.cancelMonitor()
                        self._fc.close()

                    def fd(self):
                        """Get file descriptor for monitor."""
                        return self._fc

                    def monitorFile(self, filepath):
                        """Monitor one file."""
                        self._requests.append(self._fc.monitorFile(filepath, None))

                    def pending(self):
                        """Check whether an event is pending."""
                        return self._fc.pending()

                    def nextFile(self):
                        """Get next file and return whether it has changed."""
                        event = self._fc.nextEvent()
                        # we can also use event.code2str() here,
                        # but then we need to filter the events
                        changed = {fam.Changed: 'changed',
                            fam.Created: 'created', fam.Moved: 'moved',
                            fam.Deleted: 'deleted'}.get(event.code)
                        return changed, event.filename

                break
        else:
            FAM = None
        if FAM:
            return FAM()

    class AutoReloadingAppServer(AppServer):
        """AppServer AutoReloading.

        This class adds functionality to `AppServer`, to notice changes to
        source files, including servlets, PSPs, templates or changes to the
        Webware source file themselves, and reload the server as necessary
        to pick up the changes.

        The server will also be restarted if a file which Webware *tried*
        to import is modified. This is so that changes to a file containing
        a syntax error (which would have prevented it from being imported)
        will also cause the server to restart.

        """

        ## Init ##

        def __init__(self, path=None):
            """Activate AutoReloading."""
            self._shouldRestart = False
            self._fileMonitorThread = None
            AppServer.__init__(self, path)
            try:
                if self.isPersistent() and self.setting('AutoReload'):
                    self.activateAutoReload()
            except:
                AppServer.initiateShutdown(self)
                raise

        def defaultConfig(self):
            """Return the default configuration."""
            conf = AppServer.defaultConfig(self)
            # Update with AutoReloadingAppServer specific settings
            # as defined in defaultConfig on the module level:
            conf.update(defaultConfig)
            return conf

        def shutDown(self):
            """Shut down the monitoring thread.

            This is done in addition to the normal shutdown procedure.

            """
            print 'Stopping AutoReload Monitor...'
            self.deactivateAutoReload()
            AppServer.shutDown(self)

        ## Activation of AutoReload ##

        def activateAutoReload(self):
            """Start the monitor thread."""
            if self.setting('UseImportSpy'):
                s = self._imp.activateImportSpy()
                print 'ImportSpy activated (using %s).' % s
            if not self._fileMonitorThread:
                famModules = self.setting('UseFAMModules')
                try:
                    famModules = famModules.split()
                except AttributeError:
                    pass
                if famModules and self._imp._spy:
                    # FAM will be only used when ImportSpy has been activated,
                    # since otherwise we need to poll the modules anyway.
                    try:
                        self._fam = getFAM(famModules)
                        self._pipe = None
                    except Exception, e:
                        print "Error loading FAM:", str(e)
                        self._fam = None
                    if not self._fam:
                        print 'FAM not available, fall back to polling.'
                else:
                    self._fam = None
                print 'AutoReload Monitor started,',
                if self._fam:
                    print 'using %s.' % self._fam.name()
                    target = self.fileMonitorThreadLoopFAM
                else:
                    self._pollInterval = self.setting('AutoReloadPollInterval')
                    print 'polling every %d seconds.' % self._pollInterval
                    target = self.fileMonitorThreadLoop
                self._runFileMonitor = True
                self._fileMonitorThread = t = Thread(target=target)
                t.setName('AutoReloadMonitor')
                t.start()

        def deactivateAutoReload(self):
            """Stop the monitor thread."""
            if self._fileMonitorThread:
                if self._runFileMonitor:
                    self._runFileMonitor = False
                    if self._fam:
                        if self._pipe:
                            # Send a message down the pipe to wake up the monitor thread
                            # and tell him to quit.
                            os.write(self._pipe[1], 'stop')
                            os.close(self._pipe[1])
                sys.stdout.flush()
                try:
                    self._fileMonitorThread.join()
                except Exception:
                    pass
                if self._fam:
                    if self._pipe:
                        os.close(self._pipe[0])
                        self._pipe = None
                    self._fam.close()
                    self._fam = None

        ## Restart methods ##

        def restartIfNecessary(self):
            """Check if the app server should be restarted.

            This should be called regularly to see if a restart is required.
            The server can only restart from the main thread, other threads
            can't do the restart. So this polls to see if `shouldRestart`
            has been called.

            """
            if self._shouldRestart:
                self.restart()

        def restart(self):
            """Do the actual restart.

            Call `shouldRestart` from outside the class.

            """
            sys.stdout.flush()
            sys.stderr.flush()
            # calling execve() is problematic, since the file
            # descriptors don't get closed by the OS.  This can
            # result in leaked database connections.  Instead, we
            # exit with a special return code which is recognized
            # by the AppServer script, which will restart us upon
            # receiving that code.
            sys.exit(3)

        def monitorNewModule(self, filepath, mtime=None):
            """Add new file to be monitored.

            This is a callback which ImportSpy invokes to notify us of new files
            to monitor. This is only used when we are using FAM.

            """
            self._fam.monitorFile(os.path.abspath(filepath))

        ## Internal methods ##

        def shouldRestart(self):
            """Tell the main thread to restart the server."""
            self._shouldRestart = True
            self._runFileMonitor = False

        def fileMonitorThreadLoop(self):
            """This the the main loop for the monitoring thread.

            Runs in its own thread, polling the files for changes directly
            (i.e., going through every file that's being used and checking
            its last-modified time, seeing if it's been changed since it
            was initially loaded).

            """
            while self._runFileMonitor:
                time.sleep(self._pollInterval)
                f = self._imp.updatedFile()
                if f:
                    print '*** The file', f, 'has changed.'
                    print 'Restarting AppServer...'
                    self.shouldRestart()

        def fileMonitorThreadLoopFAM(self, getmtime=os.path.getmtime):
            """Monitoring thread loop, but using the FAM library."""
            # For all of the modules which have _already_ been loaded,
            # we check to see if they've already been modified:
            f = self._imp.updatedFile()
            if f:
                print '*** The file', f, 'has changed.'
                print 'Restarting AppServer...'
                self.shouldRestart()
                return
            for f in self._imp.fileList().keys():
                self.monitorNewModule(f)
            self._imp.notifyOfNewFiles(self.monitorNewModule)
            # Create a pipe so that this thread can be notified when the
            # server is shutdown. We use a pipe because it needs to be an object
            # which will wake up the call to 'select':
            self._pipe = os.pipe()
            fds = [self._fam.fd(), self._pipe[0]], [], []
            while self._runFileMonitor:
                try:
                    # We block here until a file has been changed, or until
                    # we receive word that we should shutdown (via the pipe).
                    select.select(*fds)
                except select.error, e:
                    if e[0] == errno.EINTR:
                        continue
                    else:
                        print "Error:", e[1]
                        sys.exit(1)
                while self._runFileMonitor and self._fam.pending():
                    c, f = self._fam.nextFile()
                    if c and self._imp.fileUpdated(f):
                        print '*** The file %s has been %s.' % (f, c)
                        print 'Restarting AppServer...'
                        self.shouldRestart()
            self._imp.notifyOfNewFiles(None)