Link to issue number:

Fixes #3138

Summary of the issue:

On every focus change, NVDA runs treeInterceptorHandler.cleanup() in order to kill off any dead virtualBuffers left from no longer existing documents. Gecko_ia2 virtualBuffer's isAlive property called AccessibleObjectFromEvent as one of the ways to validate if the document still existed. However, calling this many times can be very slow, and could produce a major lag on a system with 10s of tabs open in Firefox or Chrome. This call is no longer necessary these days as we can detect this by checking if the root object has the defunct state, or its properties no longer work.

Description of how this pull request fixes the issue:

The call to AccessibleObjectFromEvent has been removed. Also, rather than using the states property on the NVDAObject to check for defaunct, use the raw IAccessible2::States property instead. This is more direct and much faster, plus we can also catch any possible COMError and treat this the same as if defunct was there.
Note that Chrome currently produces a COMError when calling IAccessible2::states when dealing with an object for a document that has closed, rather than still supporting IA2_STATE_DEFUNCT.

Testing performed:

In both Firefox and Chrome:

• Opened www.google.com/, checked the length of treeInterceptorHandler.runningTable was 1.
• Refreshed the page. Made sure that length of runningTable was still 1.
• Opened another 24 tabs to google.com. Validated that the length of runningTable was now 25.
• Timed treeInterceptorHandler.cleanup, noting that before the change it was 70 ms on my machine, but with the change now down to 5 ms.
• Closed each tab in turn, occasionally validating that length of runningTable was decreasing.
• Closed the browser and validated that runningTable was 0.

Change log entry:

Bug fixes:

• NVDA no longer becomes noticeably slower when many tabs are open in either Firefox or Chrome web browsers.