1354596 - [meta] Migrate away from `listTabs` wherever possible

Status: NEW

(DevTools :: General, enhancement, P2)

Description

[J. Ryan Stinnett [:jryans] (Use needinfo, replies may be slow)]

The DevTools `listTabs` request is a very expensive operation, especially if there are many open tabs.  It will cause us to visit every tab, load a frame script, start a debugger server, and read some data.  With lazy tab support (bug 906076), this would trigger any lazy tabs to be loaded, greatly increasing resource usage.

In many cases, we don't really need `listTabs` anyway, it just happened to exist and was easy to use for many purposes.

If you need the global actors, use the new `getRoot` from bug 1352157.
If you need a single tab, use `getTab` instead.

There are a few places (WebIDE, about:debugging) where we try enumerate all tabs, so you can choose one for debugging.  For these cases, it would be better to create something more minimal that only uses whatever data is known about the tab from the parent process, so we can avoid most of the expense.

Comment 1

[J. Ryan Stinnett [:jryans] (Use needinfo, replies may be slow)]

Current usages[1]:

* about:debugging
* Connect page
* target.root (fixed in bug 1352157)
* Legacy performance front
* WebIDE
* Various tests

[1]: http://searchfox.org/mozilla-central/search?q=listTabs(&case=true&path=

Comment 2

[Panos Astithas (he/him) [:past] (please ni?)]

Since the dependencies are now fixed, is this bug now done or do more bugs need to be filed? This is the last bug blocking bug lazytabs, which blocks bug photon-performance.

Comment 3

[J. Ryan Stinnett [:jryans] (Use needinfo, replies may be slow)]

(In reply to Panos Astithas [:past] (please needinfo?) from comment #2)
> Since the dependencies are now fixed, is this bug now done or do more bugs
> need to be filed? This is the last bug blocking bug lazytabs, which blocks
> bug photon-performance.

I don't think this needs to block lazytabs.  I believe only bug 1352157 was important regular usage, and that's fixed now.

Comment 4

[J. Ryan Stinnett [:jryans] (Use needinfo, replies may be slow)]

(Yes, there are more bugs to be filed, most items in comment 1 haven't been done yet.)