Branch: refs/heads/main
Home: https://github.com/WebKit/WebKit
Commit: 498510277e2c87eee205596bd973049eece62837
https://github.com/WebKit/WebKit/commit/498510277e2c87eee205596bd973049eece62837
Author: Tyler Wilcock <[email protected]>
Date: 2024-12-18 (Wed, 18 Dec 2024)
Changed paths:
M Source/WebKit/WebProcess/WebPage/mac/WKAccessibilityWebPageObjectBase.h
M Source/WebKit/WebProcess/WebPage/mac/WKAccessibilityWebPageObjectBase.mm
M Source/WebKit/WebProcess/WebPage/mac/WKAccessibilityWebPageObjectMac.mm
M Source/WebKit/WebProcess/WebPage/mac/WebPageMac.mm
Log Message:
-----------
AX: -[WKAccessibilityWebPageObjectMac accessibilityAttributeValue] hits the
main-thread unnecessarily
https://bugs.webkit.org/show_bug.cgi?id=284681
rdar://problem/141629794
Reviewed by Chris Fleizach.
Prior to this commit, -[WKAccessibilityWebPageObjectMac
accessibilityAttributeValue] unconditionally hit the main-thread
once to initialize accessibility (even if it had already been done so), and
potentially again depending on the attribute
requested.
Solve the first main-thread hit by adding a std::atomic<bool> that can be set
after we've initialized accessibility.
Checking an atomic bool is significantly cheaper than waiting on the
main-thread, which could be busy.
Solve the second main-thread hit by making changes necessary to serve some
attributes off the main-thread:
- Cache NSAccessibilityPrimaryScreenHeightAttribute once at the same time we
hit the main-thread to initialize
accessibility for the first time, then store it in a std::atomic<unsigned>
for subsequent use.
- Put usage of WKAccessibilityWebPageObjectBase::m_parent behind a new lock,
WKAccessibilityWebPageObjectBase::m_parentLock.
RetainPtr reference counting is inherently threadsafe, but the lock is
still necessary to ensure the main-thread
cannot overwrite m_parent with a new value while the AX thread is reading
it to serve a request.
The first attempt at making this change was reverted in
https://commits.webkit.org/287865@main because it caused
crashes in debug macOS layout tests with added assert:
ASSERT(!m_window);
This commit changes the assert to allow the window to be set to the same value,
i.e.:
ASSERT(!m_window || m_window.get() == window);
* Source/WebKit/WebProcess/WebPage/mac/WKAccessibilityWebPageObjectBase.h:
* Source/WebKit/WebProcess/WebPage/mac/WKAccessibilityWebPageObjectBase.mm:
(-[WKAccessibilityWebPageObjectBase setRemoteParent:]):
* Source/WebKit/WebProcess/WebPage/mac/WKAccessibilityWebPageObjectMac.mm:
(-[WKAccessibilityWebPageObject accessibilityAttributeValue:]):
(-[WKAccessibilityWebPageObject accessibilityAttributeSizeValue]):
(-[WKAccessibilityWebPageObject accessibilityAttributePositionValue]):
(-[WKAccessibilityWebPageObject accessibilityAttributeParentValue]):
(-[WKAccessibilityWebPageObject accessibilityAttributeWindowValue]):
(-[WKAccessibilityWebPageObject accessibilityAttributeTopLevelUIElementValue]):
Canonical link: https://commits.webkit.org/288040@main
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