[webkit-dev] Removing webkitSlice (was Re: Existing metrics for deprecated features)

Adam Barth abarth at webkit.org
Thu Sep 13 22:49:01 PDT 2012

On Thu, Sep 13, 2012 at 9:05 PM, Maciej Stachowiak <mjs at apple.com> wrote:
> On Sep 13, 2012, at 11:15 PM, Darin Fisher <darin at google.com> wrote:
> On Thu, Sep 13, 2012 at 6:16 PM, Adam Barth <abarth at webkit.org> wrote:
>> On Thu, Sep 13, 2012 at 5:13 PM, Adam Barth <abarth at webkit.org> wrote:
>> > Another metric we have is for Blob.webkitSlice:
>> >
>> > Ratio of Blob.webkitSlice calls to Blob.slice: 14.87%
>> > Ratio of Blob.webkitSlice calls to Document creation: 0.0053%
>> >
>> > It's difficult to know how to interpret this data because we don't
>> > actually correlate calls to webkitSlice with Documents or Pages.
>> > Instead, we just count the total number of calls across all Documents.
>> >  This gives us an upper bound on how many Documents (or Pages) would
>> > be affected by deleting Blob.webkitSlice, but doesn't measure that
>> > information as accurately as the data we have for mutation events.
>> Based on this data, I've posted a patch for removing Blob.webkitSlice
>> in favor of Blob.slice:
>> https://bugs.webkit.org/show_bug.cgi?id=96715
>> Adam
> So, worst case 53 out of a million pages calls webkitSlice.  But, it is easy
> to imagine that that upper bound is crazy high, and more likely a couple
> pages simply call webkitSlice a lot.  Also, given that there are so many
> more calls to Blob.slice() one could imagine that sites that call
> webkitSlice probably have fallback to Blob.slice().  Is this the hypothesis?
> Adam's data measures webkitSlice() *calls*, not just appearances of the
> symbol, so these are either sites that have fallback in the wrong direction
> (trying the prefixed version before the vanilla version), or would break
> after the removal. I've seen both problems with about similar frequency in
> the past, so a decent hypothesis is that half those webkitSlice calls will
> break.
> Safari hasn't had Blob for very long at all, so Chrome is probably more
> impacted. From my own perspective, I think the usage is low enough that it's
> worth making the change to see the fallout.
> I wonder also how likely it is that some of the webkitSlice uses are on
> Google-controlled Web properties and therefore could be fixed ahead of time.

By the way, in preparing the patch, I noticed that webkitSlice was
used by the web inspector.  Note that the data above includes the use
by the web inspector.


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