[Twisted-Python] Asynchronously initializing objects in twisted.web?

Discussion:

Nagy, Attila

2015-09-08 14:51:04 UTC

Hi,

I wonder, if I have this example program:
https://twistedmatrix.com/documents/current/web/howto/using-twistedweb.html#site-objects

how do I initialize an external resource (like a dictionary, which is
fetched from a database) with asynchronous twisted tools, but before the
HTTP server starts listening on its port?
The goal here is that the HTTP server shouldn't start until it can fetch
the desired data. Of course I can do this in a synchronous way, but it
feels so unnatural and bad practice to fetch the same stuff
synchronously on initialization and asynchronously when the
program/reactor is running (often with different libraries).

Thanks,

Phil Mayers

2015-09-08 16:07:15 UTC

Permalink

Post by Nagy, Attila
The goal here is that the HTTP server shouldn't start until it can fetch
the desired data. Of course I can do this in a synchronous way, but it
feels so unnatural and bad practice to fetch the same stuff

Load the resources in a callback using "reactor.callWhenRunning" and
only then call reactor.listenTCP or whatever.

Glyph

2015-09-08 22:21:01 UTC

Permalink

Load the resources in a callback using "reactor.callWhenRunning" and only then call reactor.listenTCP or whatever.

Just trying to use every opportunity I can to say this: don't use listenTCP, use endpoints: https://twistedmatrix.com/documents/15.4.0/core/howto/endpoints.html <https://twistedmatrix.com/documents/15.4.0/core/howto/endpoints.html>

:)

-glyph

Alexey Panyovin

2015-09-08 18:41:06 UTC

Permalink

from twisted.webimport server, resource
from twisted.internetimport reactor, defer

class Simple(resource.Resource):
isLeaf =True def render_GET(self, request):
return "<html>Hello, world!</html>" def call_me():
d = defer.Deferred()
print "Get something" d.callback("success")
return d

def run_web(_):
print "run_web" site = server.Site(Simple())
reactor.listenTCP(8080, site)

d = call_me()
d.addCallback(run_web)
reactor.run()

--
Alex

Post by Nagy, Attila
Hi,
https://twistedmatrix.com/documents/current/web/howto/using-twistedweb.html#site-objects
how do I initialize an external resource (like a dictionary, which is
fetched from a database) with asynchronous twisted tools, but before
the HTTP server starts listening on its port?
The goal here is that the HTTP server shouldn't start until it can
fetch the desired data. Of course I can do this in a synchronous way,
but it feels so unnatural and bad practice to fetch the same stuff
synchronously on initialization and asynchronously when the
program/reactor is running (often with different libraries).
Thanks,
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Nagy, Attila

2015-09-09 07:27:46 UTC

Permalink

Ah, I was under the impression that listenTCP() can only be called
before reactor.run().
I don't now where it came from.

Thanks,

Post by Alexey Panyovin
from twisted.webimport server, resource
from twisted.internetimport reactor, defer
d = defer.Deferred()
print "Get something" d.callback("success")
return d
print "run_web" site = server.Site(Simple())
reactor.listenTCP(8080, site)
d = call_me()
d.addCallback(run_web)
reactor.run()
--
Alex

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