Web Inspector: Nested ContentBrowsers / ContentViewContainers cause too many ContentView updates

• Component: Web Inspector
• Status: RESOLVED FIXED

[Joseph Pecoraro]

* SUMMARY
Nested ContentBrowsers / ContentViewContainers cause too many ContentView updates.

For resources the View hierarchy looks something like this:

  - TabBrowser
    - ContentViewContainer
      - ResourcesTabContentView (1) (ContentBrowserTabContentView with a ContentBrowser)
        - ContentViewContainer
          - ResourceClusterContentView (2) (ClusterContentView)
            - ContentViewContainer
              - TextResourceContentView (3)
                - TextEditor

In the process of showing each of the 3 ContentViews, actions are taken on its sub-views that repeat over and over depending on the nested level. ContentViewContainer.showContentView triggers BackForwardEntry.prepareToShow, and BackForwardEntry.prepareToShow triggers multiple actions which may cascade:

    - _restoreFromCookie() may cascade actions to sub ContentViews
    - shown() may cascade actions to sub ContentViews
    - updateLayout() may cascade actions to sub ContentViews

This situation is not ideal! It would be much better to reduce duplication of work here.

* STEPS TO REPRODUCE
1. Load <http://apple.com>
2. Show page source (Web Inspector, Resources Tab, Main Resource selected)
3. Scroll down the text editor
4. Switch to the Elements tab
5. Switch back to the Resources tab
  => updateLayout was called 6+ times on the TextEditor

* NOTES
- Here are annotations of the different updateLayout calls I saw in this case:
    1. prepareToShow ResourceClusterContentView triggers restoreFromCookie/showContentView for the TextResourceContentView (call shown false) and updateLayout
    2. prepareToShow->shown ResourceClusterContentView triggers shown for the TextResourceContentView (call shown true) and updateLayout
    3. prepareToShow->shown ResourceClusterContentView triggers another showContentView for TextResourceContentView (call shown false) and updateLayout
    4. prepareToShow->updateLayout ResourceClusterContentView triggers another updateLayout for TextResourceContentView
    5. prepareToShow->updateLayout Tab ContentView triggers another updateLayout down the cascade to TextResourceContentView
    6. Left Sidebar opening (I came from Elements -> Resources) triggers another updateLayout
    7. Quick Console claims it resized (probably didn't) triggers another updateLayout

[Radar WebKit Bug Importer]

<rdar://problem/21513227>

[Joseph Pecoraro]

>     1. prepareToShow ResourceClusterContentView triggers
> restoreFromCookie/showContentView for the TextResourceContentView (call
> shown false) and updateLayout

This one is particularly nasty, because this is the ResourceClusterContentView triggering an updateLayout on its sub-ContentView (TextResourceContentView) without having shown() on that view first. So the elements may not actually be in the DOM, and therefore may get incorrect / unexpected values for its views.

[Joseph Pecoraro]

>     7. Quick Console claims it resized (probably didn't) triggers another updateLayout

Eliminating this one as part of:
<https://webkit.org/b/146258> Web Inspector: Reduce QuickConsole DidResize events if it did not change

[BJ Burg]

Matt, what's the status of this bug now that we have batched async layout?

[Matt Baker]

(In reply to comment #4)
> Matt, what's the status of this bug now that we have batched async layout?

Batching layouts reduced the updates to around 3 (from around 7). The fix for https://bugs.webkit.org/show_bug.cgi?id=151058 brings the total down to two (the first of which is skipped because the TextEditor hasn't become visible yet).

Will close out when the above issue lands.