Hello, On Fri, Mar 7, 2008 at 2:05 PM, <big_tyo@inf.its-sby.edu> wrote:

hi can anyone explain to me how defer.deferredlist,defer.deferredqueue,defer.deferredlock,and defer.deferredsemaphore works?

an explanation with example will be very much help to me learning twisted

Deferreds are indeed a key feature in twisted. First, did you read these two pages? http://twistedmatrix.com/projects/core/documentation/howto/async.html http://twistedmatrix.com/projects/core/documentation/howto/defer.html (In summary: a Deferred is a promise that some result will come. To get the result, you attach functions to the deferred; they will be called when the result is available.) Then the objects you list are easy to explain: - defer.DeferredList is a deferred, which fires when all embedded Deferreds have been fired. - defer.DeferredQueue is a queue whose "get" method returns a Deferred which fires when data is available. - Similarly, defer.DeferredLock and defer.DeferredSemaphore are the usual concurrency primitives, whose "acquire" method returns a Deferred which fires when the acquisition is done. Here is an example with DeferredSemaphore and DeferredList. IMO the beauty of twisted is that the processing of one file is described in a linear fashion: fetchOneFile() seems to run in parallel. =================================================== from twisted.internet import defer, reactor from twisted.web.client import downloadPage import os # list of urls to retrieve urls = [ 'http://xxx', 'http://yyy', 'http://zzz', 'http://ttt', ] # Only 2 simultaneous downloads semaphore = defer.DeferredSemaphore(2) def fetchOneFile(url): # Process one file: # - wait to get a a semaphore slot # - fetch the url # - release the semaphore d = semaphore.acquire() def fetchData(_): print "fetch", url return downloadPage(url, os.path.basename(url)) d.addCallback(fetchData) def fetched(result): print "fetched", url, result d.addBoth(fetched) d.addBoth(lambda _:semaphore.release()) return d downloads = defer.DeferredList([fetchOneFile(url) for url in urls]) def end(result): reactor.stop() downloads.addBoth(end) reactor.run() -- Amaury Forgeot d'Arc