    #!/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.

    """

    from AppServer import AppServer
    import os
    from threading import Thread
    import time
    import sys
    import select

    try: # backward compatibility for Python < 2.3
        True, False
    except NameError:
        True, False = 1, 0

    # Attempt to use python-fam (FAM = File Alteration Monitor) instead of polling
    # to see if files have changed. Get it from http://python-fam.sourceforge.net.
    # If FAM is not available or ImportSpy is not used, we fall back to polling.
    try:
        import _fam
    except ImportError:
        _fam = None

    DefaultConfig = {
        'AutoReload': False,
        'AutoReloadPollInterval': 1, # in seconds
        'UseImportSpy': 1,
    }

    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."""
            AppServer.__init__(self, path)
            self._autoReload = False
            self._shouldRestart = False
            self._use_fam = False
            if self.isPersistent():
                if self.setting('AutoReload'):
                    self.activateAutoReload()

        def defaultConfig(self):
            """Return the default configuration."""
            conf = AppServer.defaultConfig(self)
            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...'
            sys.stdout.flush()
            self.running = 1
            self.deactivateAutoReload()
            AppServer.shutDown(self)
            sys.stdout.flush()
            sys.stderr.flush()
            self.running = 0

        ## Activation of AutoReload ##

        def activateAutoReload(self):
            """Start the monitor thread."""
            if self.setting('UseImportSpy'):
                s = self._imp.activateImportSpy()
                print 'ImportSpy activated (using %s).' % s
            self._use_fam = False
            if not self._autoReload:
                if _fam 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._fc = _fam.open()
                        self._pipe = None
                        self._use_fam = True
                    except IOError:
                        print 'FAM not available, fall back to polling.'
                        self._fc = NOne
                if self._use_fam:
                    print 'AutoReload Monitor started, using FAM.'
                    target = self.fileMonitorThreadLoopFAM
                else:
                    self._pollInterval = self.setting('AutoReloadPollInterval')
                    print 'AutoReload Monitor started,' \
                        ' polling every %d seconds.' % self._pollInterval
                    target = self.fileMonitorThreadLoop
                self._fileMonitorThread = t = Thread(target=target)
                self._autoReload = True
                t.setName('AutoReloadMonitor')
                t.start()

        def deactivateAutoReload(self):
            """Tell the monitor thread to stop.

            This should be considered as a request, not a demand.

            """
            self._autoReload = False
            if self._use_fam and self._pipe:
                # Send a message down the pipe to wake up the monitor thread
                # and tell him to quit.
                self._pipe[1].write('close')
                self._pipe[1].flush()
            try:
                self._fileMonitorThread.join()
            except:
                pass

        ## 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.

            """
            # Tavis Rudd claims: "this method can only be called by
            # the main thread.  If a worker thread calls it, the
            # process will freeze up."
            #
            # I've implemented it so that the ThreadedAppServer's
            # control thread calls this. That thread is _not_ the
            # MainThread (the initial thread created by the Python
            # interpreter), but I've never encountered any problems.
            # Most likely Tavis meant a freeze would occur if a
            # _worker_ called this.
            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.

            """
            filepath = os.path.abspath(filepath)
            self._requests.append(self._fc.monitorFile(filepath, filepath))

        ## Internal methods ##

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

        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._autoReload:
                time.sleep(self._pollInterval)
                f = self._imp.updatedFile()
                if f:
                    print '*** The file', f, 'has changed.'
                    print 'The app server is restarting now...'
                    self.shouldRestart()
                    return
            print 'Autoreload Monitor stopped.'
            sys.stdout.flush()

        def fileMonitorThreadLoopFAM(self, getmtime=os.path.getmtime):
            """Monitoring thread loop, but using the FAM library."""
            self._pipe = self.requests = None
            # 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 'The app server is restarting now...'
                self.shouldRestart()
                return
            self._requests = []
            for f in self._imp.fileList():
                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':
            r, w = os.pipe()
            r, w = os.fdopen(r, 'r'), os.fdopen(w, 'w')
            self._pipe = pipe = (r, w)
            fc = self._fc
            while self._autoReload:
                try:
                    # We block here until a file has been changed, or until
                    # we receive word that we should shutdown (via the pipe).
                    ri, ro, re = select.select([fc, pipe[0]], [], [])
                except select.error, er:
                    errnumber, strerr = er
                    if errnumber == errno.EINTR:
                        continue
                    else:
                        print strerr
                        sys.exit(1)
                while fc.pending():
                    fe = fc.nextEvent()
                    c, f = fe.code2str(), fe.userData
                    if c in ('changed', 'deleted', 'created') \
                            and self._imp.fileUpdated(f):
                        print '*** The file %s has been %s.' % (f, c)
                        print 'The app server is restarting now...'
                        self.shouldRestart()
                        return
            self._imp.notifyOfNewFiles(None)
            self._pipe = None
            for req in self._requests:
                req.cancelMonitor()
            self._requests = None
            fc.close()
            print 'Autoreload Monitor stopped'
            sys.stdout.flush()