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[whatwg] WebWorker questions

From: Shannon <shannon@arc.net.au>
Date: Tue, 12 Aug 2008 21:50:21 +1000
Message-ID: <48A178FD.9080706@arc.net.au>
A few questions and thoughts on the WebWorkers proposal:

If a WebWorker object is assigned to local variable inside a  complex 
script then it cannot be seen or stopped by the calling page. Should the 
specification offer document.workers or getAllWorkers() as a means to 
iterate over all workers regardless of where they were created?
 
Is it wise to give a web application more processing power than a single 
CPU core (or HT thread) can provide? What stops a web page hogging ALL 
cores (deliberately or not) and leaving no resources for the UI mouse or 
key actions required to close the page? (This is not a contrived 
example, I have seen both Internet Explorer on Win32 and Flash on Linux 
consume 100% CPU on several occasions). I know it's a "vendor issue" but 
should the spec at least recommend UAs leave the last CPU/core free for 
OS tasks?

Can anybody point me to an existing Javascript-based web service that 
needs more client processing power than a single P4 core?

Shouldn't an application that requires so much grunt really be written 
in Java or C as an applet, plug-in or standalone application?

If an application did require that much computation isn't it also likely 
to need a more efficient inter-"thread" messaging protocol than passing 
Unicode strings through MessagePorts? At the very least wouldn't it 
usually require the passing of binary data, complex objects or arrays 
between workers without the additional overhead of a string encode/decode?

Is the resistance to adding threads to Javascript an issue with the 
language itself, or a matter of current interpreters being non-threadsafe?

The draft spec says "protected" workers are allowed to live for a 
"user-agent-defined amount of time" after a page or browser is closed. 
I'm not really sure what possible value this could have since as an 
author we won't know whether the UA allows _any_ time and if so whether 
that time will be enough to complete our cleanup (given a vast 
discrepancy in operations-per-second across UAs and client PCs). If our 
cleanup can be arbitrarily cancelled then isn't it likely that we might 
actually leave the client or server in a worse state than if we hadn't 
tried at all? Won't this cause difficult-to-trace sporadic bugs caused 
by browser differences in what could be a rare event (a close during 
operation Y instead of during X)?

I just don't see any common cases where you'd _need_ multiple OS threads 
but still be willing to accept Javascripts' poor performance, Webworkers 
limited API, and MessagePorts' limited IO. The only things I can think 
of are new user annoyances (like delaying browser shutdown and hogging 
the CPU). Sure UA's might let us disable these things but then some 
pages won't work. The Working Draft 
<http://stuff.gsnedders.com/spec-gen/webworkers.html> lists a few 
examples, most of which appear to use non-blocking network IO and 
callbacks anyway. Other examples rely on the ability for workers to 
outlive the lifetime of the calling page (which is pretty contentious). 
The one remaining example is a contrived mathematical exercise. Is the 
scientific world really crying out for complex theorems to be solved in 
web browsers? What real-world use cases is WebWorkers supposed to solve?

I would like to see WebWorkers happen but as an author and a user I have 
serious concerns about using it in its current form. Is it really worth 
implementing or should more attention be paid to fixing non-thread-safe 
practices in the specification so future UAs can better manage threading 
internally (ie: video, IO, sockets, JS all running on seperate threads 
or even sets of threads per open tab/window)?

Shannon
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