    #!/usr/bin/env python

    """Threaded Application Server

    The AppServer is the main process of WebKit. It handles requests for
    servlets from webservers.

    ThreadedAppServer uses a threaded model for handling multiple requests.

    At one time there were other experimental execution models for AppServer,
    but none of these were successful and have been removed.
    The ThreadedAppServer/AppServer distinction is thus largely historical.

    ThreadedAppServer takes the following command line arguments:

    start: start the AppServer (default argument)
    stop: stop the currently running Apperver
    daemon: run as a daemon
    ClassName.SettingName=value: change configuration settings

    When started, the app server records its pid in appserver.pid.

    """

    from marshal import dumps, loads
    import threading, Queue, select, socket, errno, traceback

    from Common import *
    import AppServer as AppServerModule
    from PidFile import ProcessRunning
    from AutoReloadingAppServer import AutoReloadingAppServer as AppServer
    from ASStreamOut import ASStreamOut, ConnectionAbortedError
    from MiscUtils.Funcs import timestamp
    from WebUtils.Funcs import requestURI

    debug = False

    defaultConfig = {
        'Host': 'localhost', # same as '127.0.0.1'
        'EnableAdapter': True, # enable WebKit adapter
        'AdapterPort': 8086,
        'EnableMonitor': False, # disable status monitoring
        'MonitorPort': 8085,
        'EnableHTTP': True, # enable built-in HTTP server
        'HTTPPort': 8080,
        'StartServerThreads': 10, # initial number of server threads
        'MinServerThreads': 5, # minimum number
        'MaxServerThreads': 20, # maxium number
        'RequestQueueSize': 0, # means twice the maximum number of threads
        'RequestBufferSize': 8*1024, # 8 kBytes
        'ResponseBufferSize': 8*1024, # 8 kBytes
        'AddressFiles': '%s.address', # %s stands for the protocol name
        # @@ the following setting is not yet implemented
        # 'SocketType': 'inet', # inet, inet6, unix
    }

    # Need to know this value for communications
    # (note that this limits the size of the dictionary we receive
    # from the AppServer to 2,147,483,647 bytes):
    intLength = len(dumps(int(1)))

    # Initialize global variables
    server = None
    exitStatus = 0

    class NotEnoughDataError(Exception):
        pass

    class ProtocolError(Exception):
        pass

    class ThreadedAppServer(AppServer):
        """Threaded Application Server.

        `ThreadedAppServer` accepts incoming socket requests, spawns a
        new thread or reuses an existing one, then dispatches the request
        to the appropriate handler (e.g., an Adapter handler, HTTP handler,
        etc., one for each protocol).

        The transaction is connected directly to the socket, so that the
        response is sent directly (if streaming is used, like if you call
        ``response.flush()``). Thus the ThreadedAppServer packages the
        socket/response, rather than value being returned up the call chain.

        """

        ## Init ##

        def __init__(self, path=None):
            """Setup the AppServer.

            Create an initial thread pool (threads created with `spawnThread`),
            and the request queue, record the PID in a file, and add any enabled
            handlers (Adapter, HTTP, Monitor).

            """
            self._threadPool = []
            self._threadCount = 0
            self._threadUseCounter = []
            self._addr = {}
            self._requestID = 0
            self._socketHandlers = {}
            self._handlerCache = {}
            self._sockets = {}

            self._defaultConfig = None
            AppServer.__init__(self, path)

            try:
                threadCount = self.setting('StartServerThreads')
                self._maxServerThreads = self.setting('MaxServerThreads')
                self._minServerThreads = self.setting('MinServerThreads')
                self._requestQueueSize = self.setting('RequestQueueSize')
                if not self._requestQueueSize:
                    # if not set, make queue size twice the max number of threads
                    self._requestQueueSize = 2 * self._maxServerThreads
                elif self._requestQueueSize < self._maxServerThreads:
                    # otherwise do not make it smaller than the max number of threads
                    self._requestQueueSize = self._maxServerThreads
                self._requestBufferSize = self.setting('RequestBufferSize')
                self._responseBufferSize = self.setting('ResponseBufferSize')

                self._requestQueue = Queue.Queue(self._requestQueueSize)

                out = sys.stdout
                out.write('Creating %d threads' % threadCount)
                for i in range(threadCount):
                    self.spawnThread()
                    out.write(".")
                    out.flush()
                out.write("\n")

                if self.setting('EnableAdapter'):
                    self.addSocketHandler(AdapterHandler)
                if self.setting('EnableMonitor'):
                    self.addSocketHandler(MonitorHandler)
                if self.setting('EnableHTTP'):
                    from HTTPServer import HTTPAppServerHandler
                    self.addSocketHandler(HTTPAppServerHandler)

                self.readyForRequests()
            except:
                AppServer.initiateShutdown(self)
                raise

        def addSocketHandler(self, handlerClass, serverAddress=None):
            """Add socket handler.

            Adds a socket handler for `serverAddress` -- `serverAddress`
            is a tuple (*host*, *port*), where *host* is the interface
            to connect to (for instance, the IP address on a machine with
            multiple IP numbers), and *port* is the port (e.g. HTTP is on
            80 by default, and Webware adapters use 8086 by default).

            The `handlerClass` is a subclass of `Handler`, and is used to
            handle the actual request -- usually returning control back
            to ThreadedAppServer in some fashion. See `Handler` for more.

            """

            if serverAddress is None:
                serverAddress = self.address(handlerClass.settingPrefix)
            sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
            sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
            try:
                sock.bind(serverAddress)
                sock.listen(1024)
            except:
                print "Error: Can not listen for %s on %s" % (
                    handlerClass.settingPrefix, str(serverAddress))
                sys.stdout.flush()
                raise
            serverAddress = sock.getsockname() # resolve/normalize
            self._socketHandlers[serverAddress] = handlerClass
            self._handlerCache[serverAddress] = []
            self._sockets[serverAddress] = sock
            adrStr = ':'.join(map(str, serverAddress))
            print "Listening for %s on %s" % (handlerClass.settingPrefix, adrStr)
            # write text file with server address
            adrFile = self.addressFileName(handlerClass)
            if os.path.exists(adrFile):
                print "Warning: %s already exists" % adrFile
                try:
                    os.unlink(adrFile)
                except OSError: # we cannot remove the file
                    if open(adrFile).read() == adrStr:
                        return # same content, so never mind
                    else:
                        print "Error: Could not remove", adrFile
                        sys.stdout.flush()
                        raise
            try:
                f = open(adrFile, 'w')
                f.write(adrStr)
                f.close()
            except IOError:
                print "Error: Could not write", adrFile
                sys.stdout.flush()
                raise

        def isPersistent(self):
            return True

        def defaultConfig(self):
            """The default AppServer.config."""
            if self._defaultConfig is None:
                self._defaultConfig = AppServer.defaultConfig(self).copy()
                # Update with ThreadedAppServer specific settings
                # as defined in defaultConfig on the module level:
                self._defaultConfig.update(defaultConfig)
            return self._defaultConfig

        def mainloop(self, timeout=1):
            """Main thread loop.

            This is the main thread loop that accepts and dispatches
            socket requests.

            It goes through a loop as long as ``self._running > 2``.
            Setting ``self._running = 2`` asks the the main loop to end.
            When the main loop is finished, it sets ``self._running = 1``.
            When the AppServer is completely down, it sets ``self._running = 0``.

            The loop waits for connections, then based on the connecting
            port it initiates the proper Handler (e.g.,
            AdapterHandler, HTTPHandler). Handlers are reused when possible.

            The initiated handlers are put into a queue, and
            worker threads poll that queue to look for requests that
            need to be handled (worker threads use `threadloop`).

            Every so often (every 5 loops) it updates thread usage
            information (`updateThreadUsage`), and every
            ``MaxServerThreads`` * 2 loops it it will manage
            threads (killing or spawning new ones, in `manageThreadCount`).

            """

            threadCheckInterval = self._maxServerThreads * 2
            threadUpdateDivisor = 5 # grab stat interval
            threadCheck = 0

            self._running = 3 # server is in the main loop now

            try:
                while self._running > 2:

                    # block for timeout seconds waiting for connections
                    try:
                        input, output, exc = select.select(
                            self._sockets.values(), [], [], timeout)
                    except select.error, e:
                        if e[0] == errno.EINTR:
                            continue
                        else:
                            raise

                    for sock in input:
                        self._requestID += 1
                        client, addr = sock.accept()
                        serverAddress = sock.getsockname()
                        try:
                            handler = self._handlerCache[serverAddress].pop()
                        except IndexError:
                            handler = self._socketHandlers[serverAddress](self,
                                serverAddress)
                        handler.activate(client, self._requestID)
                        self._requestQueue.put(handler)

                    if threadCheck % threadUpdateDivisor == 0:
                        self.updateThreadUsage()

                    if threadCheck > threadCheckInterval:
                        threadCheck = 0
                        self.manageThreadCount()
                    else:
                        threadCheck += 1

                    self.restartIfNecessary()

            finally:
                self._running = 1

        ## Thread Management ##

        # These methods handle the thread pool. The AppServer pre-allocates
        # threads, and reuses threads for requests. So as more threads
        # are needed with varying load, new threads are spawned, and if there
        # are excess threads, then threads are removed.

        def updateThreadUsage(self):
            """Update the threadUseCounter list.

            Called periodically from `mainloop`.

            """
            count = self.activeThreadCount()
            if len(self._threadUseCounter) > self._maxServerThreads:
                self._threadUseCounter.pop(0)
            self._threadUseCounter.append(count)

        def activeThreadCount(self):
            """Get a snapshot of the number of threads currently in use.

            Called from `updateThreadUsage`.

            """
            count = 0
            for i in self._threadPool:
                if i._processing:
                    count += 1
            return count

        def manageThreadCount(self):
            """Adjust the number of threads in use.

            From information gleened from `updateThreadUsage`, we see about how
            many threads are being used, to see if we have too many threads or
            too few. Based on this we create or absorb threads.

            """

            # @@: This algorithm needs work. The edges (i.e. at the
            # minserverthreads) are tricky. When working with this,
            # remember thread creation is *cheap*.

            average = max = 0

            if debug:
                print "ThreadUse Samples:", self._threadUseCounter
            for i in self._threadUseCounter:
                average += i
                if i > max:
                    max = i
            average /= len(self._threadUseCounter)
            if debug:
                print "Average Thread Use: ", average
                print "Max Thread Use: ", max
                print "ThreadCount: ", self._threadCount

            if len(self._threadUseCounter) < self._maxServerThreads:
                return # not enough samples

            margin = self._threadCount / 2 # smoothing factor
            if debug:
                print "Margin:", margin

            if average > self._threadCount - margin and \
                self._threadCount < self._maxServerThreads:
                # Running low: double thread count
                n = min(self._threadCount,
                    self._maxServerThreads - self._threadCount)
                if debug:
                    print "Adding %s threads" % n
                for i in range(n):
                    self.spawnThread()
            elif average < self._threadCount - margin and \
                self._threadCount > self._minServerThreads:
                n = min(self._threadCount - self._minServerThreads,
                    self._threadCount - max)
                self.absorbThread(n)
            else:
                # cleanup any stale threads that we killed but haven't joined
                self.absorbThread(0)

        def spawnThread(self):
            """Create a new worker thread.

            Worker threads poll with the `threadloop` method.

            """
            if debug:
                print "Spawning new thread"
            t = threading.Thread(target=self.threadloop)
            t._processing = False
            t.start()
            self._threadPool.append(t)
            self._threadCount += 1
            if debug:
                print "New thread spawned, threadCount =", self._threadCount

        def absorbThread(self, count=1):
            """Absorb a thread.

            We do this by putting a None on the Queue.
            When a thread gets it, that tells it to exit.

            We also keep track of the threads, so after killing
            threads we go through all the threads and find the
            thread(s) that have exited, so that we can take them
            out of the thread pool.

            """
            for i in range(count):
                self._requestQueue.put(None)
                # _threadCount is an estimate, just because we
                # put None in the queue, the threads don't immediately
                # disapear, but they will eventually.
                self._threadCount -= 1
            for i in self._threadPool:
                # There may still be a None in the queue, and some
                # of the threads we want gone may not yet be gone.
                # But we'll pick them up later -- they'll wait,.
                if not i.isAlive():
                    rv = i.join() # Don't need a timeout, it isn't alive
                    self._threadPool.remove(i)
                    if debug:
                        print "Thread absorbed, real threadCount =", len(self._threadPool)

        ## Worker Threads ##

        def threadloop(self):
            """The main loop for worker threads.

            Worker threads poll the ``_requestQueue`` to find a request handler
            waiting to run. If they find a None in the queue, this thread has
            been selected to die, which is the way the loop ends.

            The handler object does all the work when its `handleRequest` method
            is called.

            `initThread` and `delThread` methods are called at the beginning and
            end of the thread loop, but they aren't being used for anything
            (future use as a hook).

            """

            self.initThread()

            t = threading.currentThread()
            t._processing = False

            try:
                while 1:
                    try:
                        handler = self._requestQueue.get()
                        if handler is None: # None means time to quit
                            if debug:
                                print "Thread retrieved None, quitting."
                            break
                        t._processing = True
                        try:
                            handler.handleRequest()
                        except Exception:
                            traceback.print_exc(file=sys.stderr)
                        t._processing = False
                        handler.close()
                    except Queue.Empty:
                        pass
            finally:
                self.delThread()
            if debug:
                print threading.currentThread(), "Quitting."

        def initThread(self):
            """Initialize thread.

            Invoked immediately by threadloop() as a hook for subclasses.
            This implementation does nothing and subclasses need not invoke super.

            """
            pass

        def delThread(self):
            """Delete thread.

            Invoked immediately by threadloop() as a hook for subclasses.
            This implementation does nothing and subclasses need not invoke super.

            """
            pass

        ## Shutting Down ##

        def shutDown(self):
            """Called on shutdown.

            Also calls `AppServer.shutDown`, but first closes all sockets
            and tells all the threads to die.

            """
            print "ThreadedAppServer is shutting down..."
            if self._running > 2:
                self._running = 2 # ask main loop to finish
                self.awakeSelect() # unblock select call in mainloop()
                sys.stdout.flush()
                for i in range(30): # wait at most 3 seconds for shutdown
                    if self._running < 2:
                        break
                    time.sleep(0.1)
            if self._sockets:
                # Close all sockets now:
                for sock in self._sockets.values():
                    sock.close()
            if self._socketHandlers:
                # Remove the text files with the server addresses:
                for handler in self._socketHandlers.values():
                    adrFile = self.addressFileName(handler)
                    if os.path.exists(adrFile):
                        try:
                            os.unlink(adrFile)
                        except OSError:
                            print "Warning: Could not remove", adrFile
            # Tell all threads to end:
            for i in range(self._threadCount):
                self._requestQueue.put(None)
            for i in self._threadPool:
                try:
                    i.join()
                except Exception:
                    pass
            # Call super's shutdown:
            AppServer.shutDown(self)

        def awakeSelect(self):
            """Awake the select() call.

            The ``select()`` in `mainloop()` is blocking, so when
            we shut down we have to make a connect to unblock it.
            Here's where we do that.

            """
            for host, port in self._sockets.keys():
                if host == '0.0.0.0':
                    # Can't connect to 0.0.0.0; use 127.0.0.1 instead
                    host = '127.0.0.1'
                sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
                try:
                    sock.connect((host, port))
                    sock.close()
                except Exception:
                    pass

        ## Misc ##

        def address(self, settingPrefix):
            """Get host address.

            The address for the Adapter (Host/interface, and port),
            as taken from ``Configs/AppServer.config``,
            settings ``Host`` and ``AdapterPort``.

            """
            try:
                return self._addr[settingPrefix]
            except KeyError:
                host = self.setting(settingPrefix + 'Host', self.setting('Host'))
                if settingPrefix == 'Adapter':
                    # jdh 2004-12-01:
                    # 'Port' has been renamed to 'AdapterPort'. However, we don't
                    # want the the default AdapterPort in DefaultConfig above to
                    # be used if a user still has 'Port' in their config file.
                    # So for now, we prefer the 'Port' setting if it exists.
                    # After a few releases we can remove this special case.
                    port = self.setting('Port', None)
                    if port is None:
                        port = self.setting(settingPrefix + 'Port')
                    else:
                        print "WARNING:", \
                            "The 'Port' setting has been renamed to 'AdapterPort'."
                        print "Please update your AppServer.config file."
                else:
                    port = self.setting(settingPrefix + 'Port')
                self._addr[settingPrefix] = (host, port)
                return self._addr[settingPrefix]

        def addressFileName(self, handlerClass):
            """Get the name of the text file with the server address."""
            return self.serverSidePath(
                self.setting('AddressFiles') % handlerClass.protocolName)

    class Handler:
        """A very general socket handler.

        Handler is an abstract superclass -- specific protocol implementations
        will subclass this. A Handler takes a socket to interact with, and
        creates a raw request.

        Handlers will be reused. When a socket is received `activate` will be
        called -- but the handler should not do anything, as it is still running
        in the main thread. The handler is put into a queue, and a worker thread
        picks it up and runs `handleRequest`, which subclasses should override.

        Several methods are provided which are typically used by subclasses.

        """

        def __init__(self, server, serverAddress):
            """Create a new socket handler.

            Each handler is attached to a specific host and port,
            and of course to the AppServer.

            """
            self._server = server
            self._serverAddress = serverAddress

        def activate(self, sock, requestID):
            """Activate the handler for processing the request.

            `sock` is the incoming socket that this handler will work with,
            and `requestID` is a serial number unique for each request.

            This isn't where work gets done -- the handler is queued after this,
            and work is done when `handleRequest` is called.

            """
            self._requestID = requestID
            self._sock = sock

        def close(self):
            """Close the socket.

            Called when the handler is finished. Closes the socket and
            returns the handler to the pool of inactive handlers.

            """
            self._sock = None
            self._server._handlerCache[self._serverAddress].append(self)

        def handleRequest(self):
            """
            Subclasses should override this -- this is where
            work gets done.
            """
            pass

        def receiveDict(self):
            """Receive a dictionary from the socket.

            Utility function to receive a marshalled dictionary from
            the socket. Returns None if the request was empty.

            """
            chunk = ''
            missing = intLength
            while missing > 0:
                block = self._sock.recv(missing)
                if not block:
                    self._sock.close()
                    if len(chunk) == 0:
                        # We probably awakened due to awakeSelect being called.
                        return None
                    else:
                        # We got a partial request -- something went wrong.
                        raise NotEnoughDataError, 'received only %d of %d bytes' \
                            ' when receiving dictLength' % (len(chunk), intLength)
                chunk += block
                missing = intLength - len(chunk)
            try:
                dictLength = loads(chunk)
            except ValueError, msg:
                # Common error: client is speaking HTTP.
                if chunk[:3] == 'GET':
                    self._sock.sendall('''\
    HTTP/1.0 505 HTTP Version Not Supported\r
    Content-type: text/plain\r
    \r
    Error: Invalid AppServer protocol: %s.\r
    Sorry, I don't speak HTTP.  You must connect via an adapter.\r
    See the Troubleshooting section of the WebKit Install Guide.\r
    ''' % msg)
                    self._sock.close()
                    return None
                print "ERROR:", msg
                print "ERROR: you can only connect to", self._serverAddress[1], \
                    "via an adapter,"
                print "       like mod_webkit or wkcgi, not with a browser."
                raise
            if type(dictLength) != type(1):
                self._sock.close()
                raise ProtocolError, "Invalid AppServer protocol"
            chunk = ''
            missing = dictLength
            while missing > 0:
                block = self._sock.recv(missing)
                if not block:
                    self._sock.close()
                    raise NotEnoughDataError, 'received only %d of %d bytes' \
                        ' when receiving dict' % (len(chunk), dictLength)
                chunk += block
                missing = dictLength - len(chunk)
            return loads(chunk)

    class MonitorHandler(Handler):
        """Monitor server status.

        Monitor is a minimal service that accepts a simple protocol,
        and returns a value indicating the status of the server.

        The protocol passes a marshalled dict, much like the Adapter
        interface, which looks like ``{'format': 'CMD'}``, where CMD
        is a command (``STATUS`` or ``QUIT``). Responds with a simple
        string, either the number of requests we've received (for
        ``STATUS``) or ``OK`` for ``QUIT`` (which also stops the server).

        """
        # @@ 2003-03 ib: we should have a RESTART command, and
        # perhaps better status indicators (number of threads, etc).

        protocolName = 'monitor'
        settingPrefix = 'Monitor'

        def handleRequest(self):
            verbose = self._server._verbose
            startTime = time.time()
            if verbose:
                print "BEGIN REQUEST"
                print asclocaltime(startTime)
            conn = self._sock
            if verbose:
                print "receiving request from", conn
            requestDict = self.receiveDict()
            if requestDict['format'] == "STATUS":
                conn.send(str(self._server._requestID))
            elif requestDict['format'] == 'QUIT':
                conn.send("OK")
                conn.close()
                self._server.shutDown()

    silentErrnos = [] # silently ignore these errors:
    for e in 'EPIPE', 'ECONNABORTED', 'ECONNRESET':
        try:
            silentErrnos.append(getattr(errno, e))
        except AttributeError:
            pass

    class TASStreamOut(ASStreamOut):
        """Response stream for ThreadedAppServer.

        The `TASStreamOut` class streams to a given socket, so that when `flush`
        is called and the buffer is ready to be written, it sends the data from the
        buffer out on the socket. This is the response stream used for requests
        generated by ThreadedAppServer.

        """

        def __init__(self, sock, autoCommit=False, bufferSize=8192):
            """Create stream.

            We get an extra `sock` argument, which is the socket which we'll
            stream output to (if we're streaming).

            """
            ASStreamOut.__init__(self, autoCommit, bufferSize)
            self._socket = sock

        def flush(self):
            """Flush stream.

            Calls `ASStreamOut.ASStreamOut.flush`, and if that returns True
            (indicating the buffer is full enough) then we send data from
            the buffer out on the socket.

            """
            result = ASStreamOut.flush(self)
            if result: # a true return value means we can send
                reslen = len(self._buffer)
                sent = 0
                bufferSize = self._bufferSize
                while sent < reslen:
                    try:
                        sent += self._socket.send(
                            self._buffer[sent:sent+bufferSize])
                    except socket.error, e:
                        if debug or e[0] not in silentErrnos:
                            print "StreamOut Error:", e
                        self._closed = True
                        raise ConnectionAbortedError
                self.pop(sent)

    class AdapterHandler(Handler):
        """Adapter handler.

        Handles the Adapter protocol (as used in mod_webkit, wkcgi,
        WebKit.cgi, HTTPAdapter, etc). This protocol passes a marshalled
        dictionary which contains the keys ``format`` and ``environ``.
        ``format`` is currently always the string ``CGI``, and ``environ``
        is a dictionary of string: string, with values like those passed
        in the environment to a CGI request (QUERY_STRING, HTTP_HOST, etc).

        The handler adds one more key, ``input``, which contains a file
        object based off the socket, which contains the body of the
        request (the POST data, for instance). It's left to Application
        to handle that data.

        """
        protocolName = 'adapter'
        settingPrefix = 'Adapter'

        def handleRequest(self):
            """Handle request.

            Creates the request dictionary, and creates a `TASStreamOut` object
            for the response, then calls `Application.dispatchRawRequest`, which
            does the rest of the work (here we just clean up after).

            """
            verbose = self._server._verbose
            self._startTime = time.time()

            requestDict = self.receiveDict()
            if not requestDict:
                return

            if verbose:
                uri = requestDict.has_key('environ') \
                    and requestURI(requestDict['environ']) or '-'
                sys.stdout.write('%5i  %s  %s\n'
                    % (self._requestID, timestamp()['pretty'], uri))

            requestDict['input'] = self.makeInput()
            requestDict['requestID'] = self._requestID

            streamOut = TASStreamOut(self._sock, bufferSize=self._server._responseBufferSize)
            transaction = self._server._app.dispatchRawRequest(requestDict, streamOut)
            try:
                streamOut.close()
                aborted = False
            except ConnectionAbortedError:
                aborted = True

            try:
                self._sock.shutdown(1)
                self._sock.close()
            except Exception:
                pass

            if verbose:
                duration = ('%0.2f secs' % (time.time() - self._startTime)).ljust(19)
                sys.stdout.write('%5i  %s  %s\n\n' % (self._requestID, duration,
                    aborted and '*connection aborted*' or uri))

            transaction._application = None
            transaction.die()
            del transaction

        def makeInput(self):
            """Create a file-like object from the socket."""
            return self._sock.makefile("rb", self._server._requestBufferSize)

    # Determines whether the main look should run in another thread.
    # On Win NT/2K/XP, we run the mainloop in a different thread because
    # it's not safe for Ctrl-C to be caught while manipulating the queues.
    # It's not safe on Linux either, but there, it appears that Ctrl-C will
    # trigger an exception in ANY thread, so this fix doesn't help.
    def runMainLoopInThread():
        return os.name == 'nt'

    # Set to False in DebugAppServer so Python debuggers can trap exceptions:
    doesRunHandleExceptions = True

    class RestartAppServerError(Exception):
        """Raised by DebugAppServer when needed."""
        pass

    _chdir = os.chdir

    def chdir(path, force=False):
        """Execute os.chdir() with safety provision."""
        assert force, \
            "You cannot reliably use os.chdir() in a threaded environment.\n" \
            + 16*" " + "Set force=True if you want to do it anway (using a lock)."
        _chdir(path)

    ## Script usage ##

    def run(workDir=None):
        """Start the server (`ThreadedAppServer`).

        `workDir` is the server-side path for the server, which may not be
        the ``Webware/WebKit`` directory (though by default it is).

        After setting up the ThreadedAppServer we call `ThreadedAppServer.mainloop`
        to start the server main loop. It also catches exceptions as a last resort.

        """
        global server
        server = None
        global exitStatus
        exitStatus = 0
        os.chdir = chdir # inhibit use of os.chdir()
        runAgain = True
        while runAgain: # looping in support of RestartAppServerError
            try:
                try:
                    runAgain = False
                    server = ThreadedAppServer(workDir)
                    if runMainLoopInThread():
                        # catch the exception raised by sys.exit so
                        # that we can re-call it in the main thread.
                        def _windowsmainloop():
                            global exitStatus
                            try:
                                server.mainloop()
                            except SystemExit, e:
                                exitStatus = e[0]
                        # Run the server thread
                        t = threading.Thread(
                            target=_windowsmainloop)
                        t.start()
                        try:
                            while server._running > 1:
                                try:
                                    time.sleep(1) # wait for interrupt
                                except Exception:
                                    if server._running < 3:
                                        raise # shutdown
                        finally:
                            t.join()
                    else:
                        server.mainloop()
                    sys.exit(exitStatus)
                except RestartAppServerError:
                    print
                    print "Restarting AppServer:"
                    sys.stdout.flush()
                    sys.stderr.flush()
                    runAgain = True
                except SystemExit, e:
                    print
                    print "Exiting AppServer%s." % (
                        e[0] == 3 and ' for reload' or '')
                    exitStatus = e[0]
                except KeyboardInterrupt:
                    print
                    print "Exiting AppServer due to keyboard interrupt."
                    exitStatus = 0
                except Exception, e:
                    if isinstance(e, IOError) and e[0] == errno.EINTR:
                        print
                        print "Exiting AppServer due to interrupt signal."
                        exitStatus = 0
                    else:
                        if doesRunHandleExceptions:
                            if not server and isinstance(e, ProcessRunning):
                                print "Error:", str(e)
                            else:
                                print
                                traceback.print_exc()
                                print
                                print "Exiting AppServer due to above exception."
                            exitStatus = 1
                        else:
                            raise
            finally:
                sys.stdout.flush()
                sys.stderr.flush()
                if server and server._running:
                    server.initiateShutdown()
                    server._closeThread.join()
                AppServerModule.globalAppServer = None
        sys.stdout.flush()
        sys.stderr.flush()
        os.chdir = _chdir # allow use of os.chdir() again
        return exitStatus

    # Signal handlers

    def shutDown(signum, frame):
        """Signal handler for shutting down the server."""
        print
        print "App server has been signaled to shutdown."
        if server and server._running > 2:
            print "Shutting down at", asclocaltime()
            sys.stdout.flush()
            server._running = 2
            if signum == SIGINT:
                raise KeyboardInterrupt
            elif signum == SIGHUP:
                sys.exit(3) # force reload
            else:
                sys.exit(0) # normal exit
        else:
            print "No running app server was found."

    try:
        # Use the threadframe module for dumping thread stack frames:
        # http://www.majid.info/mylos/stories/2004/06/10/threadframe.html
        import threadframe

        def threadDump(signum, frame):
            """Signal handler for dumping thread stack frames to stdout."""
            print
            print "App server has been signaled to attempt a thread dump."
            print
            print "Thread stack frame dump at", asclocaltime()
            sys.stdout.flush()
            frames = threadframe.dict()
            items = frames.items()
            items.sort()
            print
            print "-" * 79
            print
            for threadId, frame in items:
                print "Thread ID: %d (reference count = %d)" % (
                    threadId, sys.getrefcount(frame))
                print ''.join(traceback.format_list(traceback.extract_stack(frame)))
            items.sort()
            print "-" * 79
            sys.stdout.flush()

    except ImportError:
        # threadframe module not available
        threadDump = None

    import signal

    # Shutdown signals

    try:
        SIGHUP = signal.SIGHUP
        signal.signal(SIGHUP, shutDown)
    except AttributeError:
        SIGHUP = None
    try:
        SIGTERM = signal.SIGTERM
        signal.signal(SIGTERM, shutDown)
    except AttributeError:
        SIGTERM = None
    try:
        # this is Ctrl-C on Windows
        SIGINT = signal.SIGINT
        signal.signal(SIGINT, shutDown)
    except AttributeError:
        SIGINT = None

    if threadDump:

        # Signals for creating a thread dump

        try:
            SIGQUIT = signal.SIGQUIT
            signal.signal(SIGQUIT, threadDump)
        except AttributeError:
            SIGQUIT = None
        try:
            # this is Ctrl-Break on Windows (not Cygwin)
            SIGBREAK = signal.SIGBREAK
            signal.signal(SIGBREAK, threadDump)
        except AttributeError:
            SIGBREAK = None

    import re
    settingRE = re.compile(r'^(?:--)?([a-zA-Z][a-zA-Z0-9]*\.[a-zA-Z][a-zA-Z0-9]*)=')
    from MiscUtils import Configurable

    usage = re.search('\n.* arguments:\n\n(.*\n)*?\n', __doc__).group(0)

    def main(args):
        """Command line interface.

        Run by `Launch`, this is the main entrance and command-line interface
        for ThreadedAppServer.

        """
        function = run
        daemon = False
        workDir = None
        for i in args[:]:
            if settingRE.match(i):
                match = settingRE.match(i)
                name = match.group(1)
                value = i[match.end():]
                Configurable.addCommandLineSetting(name, value)
            elif i == "stop":
                function = AppServerModule.stop
            elif i == "daemon":
                daemon = True
            elif i == "start":
                pass
            elif i[:8] == "workdir=":
                workDir = i[8:]
            else:
                print usage
                return
        if daemon:
            if os.name == "posix":
                pid = os.fork()
                if pid:
                    sys.exit()
            else:
                print "Daemon mode not available on your OS."
        return function(workDir=workDir)