def _wait_for_exit_or_signal(self, ready_callback=None):
        status = None
        signo = 0

        LOG.debug(_('Full set of CONF:'))
        CONF.log_opt_values(LOG, std_logging.DEBUG)

        try:
            if ready_callback:
                ready_callback()
            super(ServiceLauncher, self).wait()
        except SignalExit as exc:
            signame = _signo_to_signame(exc.signo)
            LOG.info(_('Caught %s, exiting'), signame)
            status = exc.code
            signo = exc.signo
        except SystemExit as exc:
            status = exc.code
        finally:
            self.stop()
            if rpc:
                try:
                    rpc.cleanup()
                except Exception:
                    # We're shutting down, so it doesn't matter at this point.
                    LOG.exception(_('Exception during rpc cleanup.'))

        return status, signo

    def _wait_child(self):
        try:
            # Don't block if no child processes have exited
            pid, status = os.waitpid(0, os.WNOHANG)
            if not pid:
                return None
        except OSError as exc:
            if exc.errno not in (errno.EINTR, errno.ECHILD):
                raise
            return None

        if os.WIFSIGNALED(status):
            sig = os.WTERMSIG(status)
            LOG.info(_('Child %(pid)d killed by signal %(sig)d'),
                     dict(pid=pid, sig=sig))
        else:
            code = os.WEXITSTATUS(status)
            LOG.info(_('Child %(pid)s exited with status %(code)d'),
                     dict(pid=pid, code=code))

        if pid not in self.children:
            LOG.warning(_('pid %d not in child list'), pid)
            return None

        wrap = self.children.pop(pid)
        wrap.children.remove(pid)
        return wrap

        def _inner():
            if initial_delay:
                greenthread.sleep(initial_delay)

            try:
                while self._running:
                    start = timeutils.utcnow()
                    self.f(*self.args, **self.kw)
                    end = timeutils.utcnow()
                    if not self._running:
                        break
                    delay = interval - timeutils.delta_seconds(start, end)
                    if delay <= 0:
                        LOG.warn(_('task run outlasted interval by %s sec') %
                                 -delay)
                    greenthread.sleep(delay if delay > 0 else 0)
            except LoopingCallDone as e:
                self.stop()
                done.send(e.retvalue)
            except Exception:
                LOG.exception(_('in fixed duration looping call'))
                done.send_exception(*sys.exc_info())
                return
            else:
                done.send(True)

    def _error(self, inner, req):
        LOG.exception(_("Caught error: %s"), unicode(inner))

        safe = getattr(inner, 'safe', False)
        headers = getattr(inner, 'headers', None)
        status = getattr(inner, 'code', 500)
        if status is None:
            status = 500

        msg_dict = dict(url=req.url, status=status)
        LOG.info(_("%(url)s returned with HTTP %(status)d") % msg_dict)
        outer = self.status_to_type(status)
        if headers:
            outer.headers = headers
        # NOTE(johannes): We leave the explanation empty here on
        # purpose. It could possibly have sensitive information
        # that should not be returned back to the user. See
        # bugs 868360 and 874472
        # NOTE(eglynn): However, it would be over-conservative and
        # inconsistent with the EC2 API to hide every exception,
        # including those that are safe to expose, see bug 1021373
        if safe:
            if isinstance(inner.msg_fmt, gettextutils.Message):
                user_locale = req.best_match_language()
                inner_msg = gettextutils.translate(
                        inner.msg_fmt, user_locale)
            else:
                inner_msg = unicode(inner)
            outer.explanation = '%s: %s' % (inner.__class__.__name__,
                                            inner_msg)

        notifications.send_api_fault(req.url, status, inner)
        return wsgi.Fault(outer)

def limited(items, request, max_limit=CONF.osapi_max_limit):
    """
    Return a slice of items according to requested offset and limit.
    """
    try:
        offset = int(request.GET.get('offset', 0))
    except ValueError:
        msg = _('offset param must be an integer')
        raise webob.exc.HTTPBadRequest(explanation=msg)

    try:
        limit = int(request.GET.get('limit', max_limit))
    except ValueError:
        msg = _('limit param must be an integer')
        raise webob.exc.HTTPBadRequest(explanation=msg)

    if limit < 0:
        msg = _('limit param must be positive')
        raise webob.exc.HTTPBadRequest(explanation=msg)

    if offset < 0:
        msg = _('offset param must be positive')
        raise webob.exc.HTTPBadRequest(explanation=msg)

    limit = min(max_limit, limit or max_limit)
    range_end = offset + limit
    return items[offset:range_end]

    def _start_child(self, wrap):
        if len(wrap.forktimes) > wrap.workers:
            # Limit ourselves to one process a second (over the period of
            # number of workers * 1 second). This will allow workers to
            # start up quickly but ensure we don't fork off children that
            # die instantly too quickly.
            if time.time() - wrap.forktimes[0] < wrap.workers:
                LOG.info(_('Forking too fast, sleeping'))
                time.sleep(1)

            wrap.forktimes.pop(0)

        wrap.forktimes.append(time.time())

        pid = os.fork()
        if pid == 0:
            launcher = self._child_process(wrap.service)
            while True:
                self._child_process_handle_signal()
                status, signo = self._child_wait_for_exit_or_signal(launcher)
                if not _is_sighup_and_daemon(signo):
                    break
                launcher.restart()

            os._exit(status)

        LOG.info(_('Started child %d'), pid)

        wrap.children.add(pid)
        self.children[pid] = wrap

        return pid

    def run_periodic_tasks(self, context, raise_on_error=False):
        """
        Tasks to be run at a periodic interval.
        """
        idle_for = DEFAULT_INTERVAL
        for task_name, task in self._periodic_tasks:
            full_task_name = ".".join([self.__class__.__name__, task_name])

            now = timeutils.utcnow()
            spacing = self._periodic_spacing[task_name]
            last_run = self._periodic_last_run[task_name]

            # If a periodic task is _nearly_ due, then we'll run it early
            if spacing is not None and last_run is not None:
                due = last_run + datetime.timedelta(seconds=spacing)
                if not timeutils.is_soon(due, 0.2):
                    idle_for = min(idle_for, timeutils.delta_seconds(now, due))
                    continue

            if spacing is not None:
                idle_for = min(idle_for, spacing)

            LOG.debug(_("Running periodic task %(full_task_name)s"), {"full_task_name": full_task_name})
            self._periodic_last_run[task_name] = timeutils.utcnow()

            try:
                task(self, context)
            except Exception as e:
                if raise_on_error:
                    raise
                LOG.exception(_("Error during %(full_task_name)s: %(e)s"), {"full_task_name": full_task_name, "e": e})
            time.sleep(0)

        return idle_for

def _get_int_param(request, param):
    """
    Extract integer param from request or fail.
    """
    try:
        int_param = int(request.GET[param])
    except ValueError:
        msg = _('%s param must be an integer') % param
        raise webob.exc.HTTPBadRequest(explanation=msg)
    if int_param < 0:
        msg = _('%s param must be positive') % param
        raise webob.exc.HTTPBadRequest(explanation=msg)
    return int_param

def _get_not_supported_column(col_name_col_instance, column_name):
    try:
        column = col_name_col_instance[column_name]
    except KeyError:
        msg = _("Please specify column %s in col_name_col_instance "
                "param. It is required because column has unsupported "
                "type by sqlite).")
        raise ColumnError(msg % column_name)

    if not isinstance(column, Column):
        msg = _("col_name_col_instance param has wrong type of "
                "column instance for column %s It should be instance "
                "of sqlalchemy.Column.")
        raise ColumnError(msg % column_name)
    return column

    def __init__(self, name, app, host='0.0.0.0', port=0, pool_size=None,
                       protocol=eventlet.wsgi.HttpProtocol, backlog=128,
                       use_ssl=False, max_url_len=None):
        """
        Initialize, but do not start, a WSGI server.
        初始化但并不启动一个WSGI服务；
        """
        # Allow operators to customize http requests max header line size.
        eventlet.wsgi.MAX_HEADER_LINE = CONF.max_header_line
        self.name = name
        self.app = app
        self._server = None
        self._protocol = protocol
        self._pool = eventlet.GreenPool(pool_size or self.default_pool_size)
        
        self._logger = logging.getLogger("xdrs.%s.wsgi.server" % self.name)
        self._wsgi_logger = logging.WritableLogger(self._logger)
        
        self._use_ssl = use_ssl
        self._max_url_len = max_url_len

        if backlog < 1:
            raise exception.InvalidInput(
                    reason='The backlog must be more than 1')

        bind_addr = (host, port)
        # TODO(dims): eventlet's green dns/socket module does not actually
        # support IPv6 in getaddrinfo(). We need to get around this in the
        # future or monitor upstream for a fix
        try:
            info = socket.getaddrinfo(bind_addr[0],
                                      bind_addr[1],
                                      socket.AF_UNSPEC,
                                      socket.SOCK_STREAM)[0]
            family = info[0]
            bind_addr = info[-1]
        except Exception:
            family = socket.AF_INET

        try:
            self._socket = eventlet.listen(bind_addr, family, backlog=backlog)
        except EnvironmentError:
            LOG.error(_("Could not bind to %(host)s:%(port)s"),
                      {'host': host, 'port': port})
            raise

        (self.host, self.port) = self._socket.getsockname()[0:2]
        LOG.info(_("%(name)s listening on %(host)s:%(port)s") % self.__dict__)

def initialize_if_enabled():
    backdoor_locals = {
        'exit': _dont_use_this,      # So we don't exit the entire process
        'quit': _dont_use_this,      # So we don't exit the entire process
        'fo': _find_objects,
        'pgt': _print_greenthreads,
        'pnt': _print_nativethreads,
    }

    if CONF.backdoor_port is None:
        return None

    start_port, end_port = _parse_port_range(str(CONF.backdoor_port))

    def displayhook(val):
        if val is not None:
            pprint.pprint(val)
    sys.displayhook = displayhook

    sock = _listen('localhost', start_port, end_port, eventlet.listen)

    # In the case of backdoor port being zero, a port number is assigned by
    # listen().  In any case, pull the port number out here.
    port = sock.getsockname()[1]
    LOG.info(_('Eventlet backdoor listening on %(port)s for process %(pid)d') %
             {'port': port, 'pid': os.getpid()})
    eventlet.spawn_n(eventlet.backdoor.backdoor_server, sock,
                     locals=backdoor_locals)
    return port

 def read(self, i=None):
     result = self.data.read(i)
     self.bytes_read += len(result)
     if self.bytes_read > self.limit:
         msg = _("Request is too large.")
         raise webob.exc.HTTPRequestEntityTooLarge(explanation=msg)
     return result

 def coerce(self, obj, attr, value):
     if not isinstance(value, list):
         raise ValueError(_('A list is required here'))
     for index, element in enumerate(list(value)):
         value[index] = self._element_type.coerce(
                 obj, '%s[%i]' % (attr, index), element)
     return value

    def __init__(self, message=None, **kwargs):
        self.kwargs = kwargs

        if 'code' not in self.kwargs:
            try:
                self.kwargs['code'] = self.code
            except AttributeError:
                pass

        if not message:
            try:
                message = self.msg_fmt % kwargs

            except Exception:
                exc_info = sys.exc_info()
                # kwargs doesn't match a variable in the message
                # log the issue and the kwargs
                LOG.exception(_('Exception in string format operation'))
                for name, value in kwargs.iteritems():
                    LOG.error("%s: %s" % (name, value))

                if CONF.fatal_exception_format_errors:
                    raise exc_info[0], exc_info[1], exc_info[2]
                else:
                    # at least get the core message out if something happened
                    message = self.msg_fmt

        super(XdrsException, self).__init__(message)

    def obj_class_from_name(cls, objname, objver):
        """
        Returns a class from the registry based on a name and version.
        """
        if objname not in cls._obj_classes:
            LOG.error(_('Unable to instantiate unregistered object type '
                        '%(objtype)s') % dict(objtype=objname))
            raise exception.UnsupportedObjectError(objtype=objname)

        latest = None
        compatible_match = None
        for objclass in cls._obj_classes[objname]:
            if objclass.VERSION == objver:
                return objclass

            version_bits = tuple([int(x) for x in objclass.VERSION.split(".")])
            if latest is None:
                latest = version_bits
            elif latest < version_bits:
                latest = version_bits

        if compatible_match:
            return compatible_match

        latest_ver = '%i.%i' % latest
        raise exception.IncompatibleObjectVersion(objname=objname,
                                                  objver=objver,
                                                  supported=latest_ver)

        def wrapped(*args, **kwargs):
            try:
                return f(*args, **kwargs)
            except Exception as exc:
                if isinstance(exc, webob.exc.WSGIHTTPException):
                    if isinstance(errors, int):
                        t_errors = (errors,)
                    else:
                        t_errors = errors
                    if exc.code in t_errors:
                        raise
                elif isinstance(exc, exception.PolicyNotAuthorized):
                    # Note(cyeoh): Special case to handle
                    # PolicyNotAuthorized exceptions so every
                    # extension method does not need to wrap authorize
                    # calls. ResourceExceptionHandler silently
                    # converts NotAuthorized to HTTPForbidden
                    raise
                elif isinstance(exc, exception.ValidationError):
                    # Note(oomichi): Handle a validation error, which
                    # happens due to invalid API parameters, as an
                    # expected error.
                    raise

                LOG.exception(_("Unexpected exception in API method"))
                raise webob.exc.HTTPInternalServerError()

 def deprecated(self, msg, *args, **kwargs):
     stdmsg = _("Deprecated: %s") % msg
     if CONF.fatal_deprecations:
         self.critical(stdmsg, *args, **kwargs)
         raise DeprecatedConfig(msg=stdmsg)
     else:
         self.warn(stdmsg, *args, **kwargs)

 def __iter__(self):
     for chunk in self.data:
         self.bytes_read += len(chunk)
         if self.bytes_read > self.limit:
             msg = _("Request is too large.")
             raise webob.exc.HTTPRequestEntityTooLarge(explanation=msg)
         else:
             yield chunk

def _read_deleted_filter(query, db_model, read_deleted):
    if 'deleted' not in db_model.__table__.columns:
        raise ValueError(_("There is no `deleted` column in `%s` table. "
                           "Project doesn't use soft-deleted feature.")
                         % db_model.__name__)

    default_deleted_value = db_model.__table__.c.deleted.default.arg
    if read_deleted == 'no':
        query = query.filter(db_model.deleted == default_deleted_value)
    elif read_deleted == 'yes':
        pass  # omit the filter to include deleted and active
    elif read_deleted == 'only':
        query = query.filter(db_model.deleted != default_deleted_value)
    else:
        raise ValueError(_("Unrecognized read_deleted value '%s'")
                         % read_deleted)
    return query

 def basic_config_check(self):
     """Perform basic config checks before starting processing."""
     try:
         with utils.tempdir():
             pass
     except Exception as e:
         LOG.error(_('Temporary directory is invalid: %s'), e)
         sys.exit(1)