"Refresh" a request using the Periodic Callback

[Irene Bontà]

Hi all I have this part of code:

self.lock_tables("write", ['confcommands'])
self.db.execute("INSERT INTO confcommands (network_id, ntype, timestamp, command) \
                 VALUES (%s,%s,%s,%s)", nid, mynet_type, ts, cmdjson)
self.unlock_tables();

time.sleep(5)

como_url = "".join(['http://', options.como_address, ':', options.como_port, 
                            '/ztc_config?netid=0&opcode_group=0&opcode=0&start=-20s&end=-1s'])

http_client = AsyncHTTPClient()
request = tornado.httpclient.HTTPRequest(url=como_url, connect_timeout=5.0, request_timeout=5.0)
response = yield tornado.gen.Task(http_client.fetch, request)

I write a command to send to a sensor into the DB. Then, I make an http request to another DB to read the response of the sensor. There's a time between the reading of the command by the sensor and its response with the elaborations.

How can I use Periodic Callback to periodically resend the request without I have to put a blocking time.sleep in my code? Help me please, I don't know where to begin...

[A. Jesse Jiryu Davis]

You can use PeriodicCallback like:

from tornado import gen, ioloop

loop = ioloop.IOLoop.instance()

@gen.engine
def f():
    print 'go!'

# Every 1000 ms
periodic = ioloop.PeriodicCallback(f, 1000)
periodic.start()
loop.start()

f needn't be decorated with gen.engine in this example, of course, but in your code you'll probably want to do some I/O in f so it should be a generator, thus I've used gen.engine. You could also just use a for loop:

import datetime

@gen.engine
def f():
    while True:
        # Pause 1 second while other tasks can run on the loop
        yield gen.Task(loop.add_timeout, datetime.timedelta(seconds=1))
        print 'go!'

f()
loop.start()

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[Ben Darnell]

Even though it's possible to stop a PeriodicCallback after it's been started, it's kind of cumbersome to start and stop them.  I recommend only using PeriodicCallbacks for things that you want to run in the background forever, and in other cases use add_timeout directly.  You can generally replace "time.sleep(x)" with "yield gen.Task(IOLoop.instance().add_timeout, datetime.timedelta(seconds=x))"  (and in Tornado 3.0 you can use IOLoop.current() instead of IOLoop.instance()).

-Ben

[Irene Bontà]

Yes Ben, thank you. I would use a PeriodicCallback in the background forever. But I don't know how to do.

I want to start the periodic callback in the main of my Tornado server. The periodic callback call a function that uses into itself methods that are defined in a Base Handler class... I don't know how to put this function because if I put the function as static in the server, she don't "see" methods are in the class. If I put the function in the class, the main don't know the function when the server starts....

Irene

[A. Jesse Jiryu Davis]

Irene, if you have methods that are executed periodically forever, then I don't think those methods should be defined in a RequestHandler. A RequestHandler handles HTTP requests. But your periodically executed methods aren't responding to an HTTP request. So take the methods out of the BaseHandler and define them at the regular module scope.

[Irene Bontà]

Yes I know...

And insted if I write something like this:

    class SensorSendHandler(BaseHandler):

    @tornado.web.authenticated

    @tornado.web.asynchronous

    @tornado.gen.engine

    def get(self, nid, sid):

........

.................

periodic = tornado.ioloop.PeriodicCallback(SensorSendHandler.check_commands_response(), 5000)

        periodic.start()

.....................

    @staticmethod

    def check_commands_response():

        print("ciao")

        nets = self.db.query("SELECT DISTINCT netid from networks")

        

        for net in nets:

            got_commands_response(net)

    

    @staticmethod

    def got_commands_response(netid):

        como_url = "".join("http://131.114.52.207:44444/ztc_config?netid=" \

                   + netid + "&opcode_group=0&opcode=0&start=-10s&end=-1s")

        

        http_client = AsyncHTTPClient()

        #asynchronous alternative to time.sleep

        yield tornado.gen.Task(tornado.ioloop.IOLoop.instance().add_timeout, time.time() + 5)

        response = yield tornado.gen.Task(http_client.fetch, como_url)

        

        print response

How can I call the check_commands_response function passing "self" to it?

[A. Jesse Jiryu Davis]

I think you should move both check_commands_response and got_commands_response *out* of BaseHandler. They don't belong in a handler. I don't think they belong in any class at all—they're just functions. Then these methods won't require a "self" parameter.

Both methods must be decorated with @gen.engine. See my blog post about calling one gen.engine-decorated function from another.

Also, you should pass check_commands_response, not check_commands_response(), to

PeriodicCallback.

[Irene Bontà]

So, I've put the PeriodicCallback call in the SensorSendHandler like this:

        periodic = tornado.ioloop.PeriodicCallback(check_commands_response, 5000)

        periodic.start()

And in the global space I've written like this:

@tornado.gen.engine

def check_commands_response():

    print("ciao")

    nets = db.query("SELECT DISTINCT netid from networks")

    

    for net in nets:

        got_commands_response(net)

@tornado.gen.engine

def got_commands_response(netid):

    como_url = "".join("http://131.114.52.207:44444/ztc_config?netid=" \

               + netid + "&opcode_group=0&opcode=0&start=-10s&end=-1s")

    

    http_client = AsyncHTTPClient()

    #asynchronous alternative to time.sleep

    yield tornado.gen.Task(tornado.ioloop.IOLoop.instance().add_timeout, time.time() + 5)

    response = yield tornado.gen.Task(http_client.fetch, como_url)

    

    print response

without the self reference....

But obviously now I have this error:

NameError: global name 'db' is not defined

[A. Jesse Jiryu Davis]

Yup. How do you connect to your database? You need some globally available reference to the db.

[Irene Bontà]

Yes. But it's defined in the Application class...

class Application(tornado.web.Application):

    def __init__(self):

        # define Nodes for the Application graph

        handlers = [ 

            (r"/*", HomeHandler),

            #(r"/auth/login", AuthLoginHandler),

            (r"/auth/login", FakeAuthLoginHandler),

            (r"/auth/logout", AuthLogoutHandler),

            (r"/networks/*", NetworksHandler),

            (r"/staticpage/([a-z]+)/*", StaticPageHandler),

            (r"/networks/edit", NetworkEditHandler),

            (r"/networks/delete", NetworkDeleteHandler),

            (r"/networks/([0-9]+)/status/*", NetworkStatusHandler),

            (r"/networks/([0-9]+)/config/*", NetworkConfHandler),

            (r"/networks/([0-9]+)/sensors/*", NetworkSensorsHandler),

            (r"/networks/([0-9]+)/sensors/([0-9]+)/*", SensorHandler),

            (r"/networks/([0-9]+)/send/*", NetworkSendHandler),

            (r"/networks/([0-9]+)/sensors/([0-9]+)/send/*", SensorSendHandler),

            (r"/networks/([0-9]+)/sensors/edit/*", SensorEditHandler),

            (r"/networks/([0-9]+)/sensors/delete/*", SensorDeleteHandler),

            (r"/networks/([0-9]+)/sensors/([0-9]+)/data/*", SensorDataHandler),

            (r"/networks/([0-9]+)/unreg", NetworkUnregSensorsHandler),

            (r"/networks/types", NetworksTypesHandler),

            (r"/networks/([0-9]+)/rights", NetworkRightsHandler),

            (r"/networks/([0-9]+)/sensors/([0-9]+)/rights", SensorRightsHandler),

            (r"/networks/([0-9]+)/all*", NetworkAllRightsHandler),

            (r"/networks/([0-9]+)/sensors/([0-9]+)/all*", SensorAllRightsHandler)

        ]

        # Define Tornado configuration

        settings = dict(

            title=u"MetroPower",

            template_path=os.path.join(os.path.dirname(__file__), "templates"),

            static_path=os.path.join(os.path.dirname(__file__), "static"),

            xsrf_cookies=True, # Use Cross-Site attack secured cookies?

            ui_modules={"SensorGraphSparkline": SensorGraphSparklineModule},

            # TODO: generate a new cookie secret

            cookie_secret="11oETzKXQAGaYdkL5gEmGeJJFuYh7EQnp2XdTP1o/Vo=",

            login_url="/auth/login", # Default login url

            autoescape=None, # Do not automatically esacape everything when

                               # rendering templates

            debug=True, # Automatically reload on source file saving + no cache 

        )

        # Initialize the Web Application

        tornado.web.Application.__init__(self, handlers, **settings)

        # Open DB connection. Shared among all handlers.

        self.db = tornado.database.Connection(

                host=options.mysql_host, database=options.mysql_database,

                user=options.mysql_user, password=options.mysql_password)

[A. Jesse Jiryu Davis]

So do that in the global scope instead! Or you could define your check_commands_response function as a method of application, then:

        periodic = tornado.ioloop.PeriodicCallback(app.check_commands_response, 5000)