Deferred Gratification

Deferred Gratification Patterns of asynchronous flow of control with Twisted deferreds Terry Jones terry@fluidinfo.com @terrycojones

Not an intro talk. Sorry! • Assume you understand Deferreds • Assume you understand async

Read defer.py • Lots of people don’t • Much of it is beautiful • Deferreds seem cryptic • They’re are actually very simple

Building blocks Simple functions that help with deferreds • succeed • fail • maybeDeferred Classes that build on simple deferreds • DeferredList • DeferredQueue • DeferredSemaphore • DeferredLock

Deferreds let you replace synchronous data structures with elegant asynchrnous equivalents

Some of our classes http://jon.es/other/europython-2010-deferreds.tar.bz2 • tee • RetryingCall • DeferredPooler } • ControllableDeferred • DeferredPool rdq.py • ResizableDispatchQueue

DeferredPooler client client server whatever client

DeferredPooler client fe tc h( x, y) client server whatever client

DeferredPooler client fe tc h( x, y) fetch(x,y) client server whatever client

DeferredPooler client fe tc h( x, y) fetch(x,y) fetch(x,y) client server whatever client

DeferredPooler client fe tc h( x, y) fetch(x,y) fetch(x,y) client server whatever , y) ( x ch f et client

DeferredPooler client fe tc h( x, y) fetch(x,y) fetch(x,y) client server whatever result , y) ( x ch f et client

DeferredPooler client fe tc re h( su x, lt y) fetch(x,y) fetch(x,y) client server whatever result result , y) x h( tc fe ult r es client

Normal Deferred 1 d = someFunc(arg1,arg2) cb1 cb2 cb3 2 d.addCallback() cb1 cb2 cb3 cb4 cb5 3 # Hope d fires!

Controllable Deferred 1 d = ControllableDeferred(someFunc,arg1,arg2) cb1 cb2 cb3 2 d.addCallback() cb1 cb2 cb3 ? cb4 cb5 3 # If call to someFunc fires, call d. # Allow caller to call d.cancel

RetryingCall Replace something like this d = getPage(url) With this r = RetryingCall(getPage, url) d = r.start()

Resizable Dispatch Queue Tickery adder RDQ pending WWW put put a b c d underway Twitter e doWork f FluidDB call g admin pause, resume, stop, size, widen, narrow, underway, cancel

Deferred Gratification

by Terry Jones

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Deferred Gratification Presentation Transcript