Re: Race condition?

I'll try to fix the polyfill soon.  

I'm now seeing that I may have mis-read the spec.  It's a little unfortunate that the HTML5 spec linked from the references [1] does not actually contain the phrase "queue a task"; for that you have to click through to the separate page for APIs [2].

The Promises model still seems more intuitive to me, so I support the note in the spec about moving CryptoOperation to a Promises-like API.

--Richard


[1] <http://www.w3.org/html/wg/drafts/html/master/Overview.html> 
[2] <http://www.w3.org/html/wg/drafts/html/master/webappapis.html#event-loops>


On Mar 25, 2013, at 4:50 PM, Ryan Sleevi <sleevi@google.com> wrote:

> 
> 
> 
> On Mon, Mar 25, 2013 at 1:20 PM, Richard Barnes <rbarnes@bbn.com> wrote:
> Hey all,
> 
> Section 1. Is there a problem?
> 
> I'm wondering if the "single-shot" syntax for encrypt/decrypt/sign/verify introduces a race condition for developers.  Suppose I write the following two lines:
> 
> var op = window.crypto.encrypt(alg, key, buffer);
> op.oncomplete = function(e) { /* do stuff with result */ }
> 
> The encrypt() call is asynchronous, so the "complete" event may have already fired before the "oncomplete" handler is set.  So my handler never gets called, which makes my app not work.
> 
> 
> Section 2. How do we solve the problem
> 
> It seems like there are two possible approaches here:
> 1. Delay the event
> 2. Provide explicit sequencing (Promises or synchronous call)
> 
> FWIW, PolyCrypt resolves takes the former approach right now.  An operation caches the last event that it fired of each type.  Then when a listener is registered, it can get the cached event.  This is basically the same as the Promises approach, but with dirtier syntax.
> 
> In other words, it seems like implementing a Promises-style interface should be a high priority, because otherwise there's non-deterministic behavior.
> 
> --Richard
> 
> Just to be clear, your polyfill is non-comformant then.
> 
> You can easily simulate the "queue a task" by using a setTimeout value of 0, which will ensure that control is yielded back to the event loop before continuing processing. 
>

Received on Monday, 25 March 2013 23:01:48 UTC