[webkit-dev] GlobalScript in WebKit

Oliver Hunt oliver at apple.com
Mon Nov 30 20:52:38 PST 2009

On Nov 30, 2009, at 8:31 PM, Darin Fisher wrote:

> On Mon, Nov 30, 2009 at 7:55 PM, Maciej Stachowiak <mjs at apple.com> wrote:
> On Nov 30, 2009, at 6:16 PM, Drew Wilson wrote:
>> Following up, I think this highlights the distinct set of use cases that shared workers and shared script address:
>> SharedWorkers are a great platform for when you have a single database that is shared across multiple instances of your web app, and you want to coordinate updates to that database. I can imagine sharing a single connection to the server, etc via SharedWorkers.
>> SharedScripts are a good platform for when you want to share data/code (for example, the immense body of Javascript used to implement the Gmail UI) across multiple windows. I can't speak to whether passing a hidden iframe between windows as was suggested in the other thread would address this use case sufficiently. 
> Would it be fair to say the goal for SharedScript is just to share code and data (to reduce memory use of multiple instances of GMail), and not network connections, timers, or other APIs based on async callbacks (assuming those either remain per-Window or are in the SharedWorker)? If so, then it would pretty much completely be handled by sharing of some arbitrary JavaScript object, possibly arranged by SharedWorker.
> Sharing an out-of-document HTMLIFrameElement would almost even account for timers and the like, except that currently in WebKit a frame's Window does not exist and its contents are not loaded if the frame is not rendered.
> XHRs also don't work after the frame has been unloaded.

I think my primary concern is that the use of _Shared_ or _Global_ in the name implies behaviour similar to that of SharedWorker, which is not guaranteed, likewise origin based object lifetime can trivially result in differences in behaviour between browser (which when coupled with the naming issue) could easily become a headache for developers.

It seems that what is really wanted is a Worker context that isn't actually a separate thread, so avoiding the need for postMessage, and have it be explicitly instantiated so as to avoid any browser-architecture derived behavioural differences. eg.

var mySharedContext = new SharableScriptContext("script to load here?");
mySharedContext.onload = function() {
// or should it be
// mySharedContext.src = "script to load here?"

Later on:
function doSomethingCoolThatNeedsANewWindow() {
    var win = window.open(...);
    win.onload = function() {

// Note handling the passing of the shared context is entirely developer defined -- eg. the only spec behaviour is the 'new SharableScriptContext' everything else is whatever the developers wants
// Note 2: I am truly awful at naming things so these names are mostly chosen to clarify unambiguously-ish what i believe the goal is

The downside is that it requires manually passing the context to new windows, the plus side is that it doesn't provide (or imply) behaviour that may be ('necessarily') different between UAs.


> -Darin

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