WebKit Igalia Periodical #63

Delivered a number of changes that have strengthened WPE WebKit and WebKitGTK's behaviour around real-time thread promotion and demotion:

• Real-time soft and hard limits are now set both when sched_setscheduler or D-Bus based paths are taken (i.e. through rtkit or the corresponding XDG portal), with the soft limit set at 80% of the hard one.
• This means WebKit now has time to gracefully handle SIGXCPU, and will do it in an async-signal-safe manner.
• Additionally, the NetworkProcess' Cache Storage thread is now defined as QOS::UserInitiated on Linux, which no longer maps to real-time priority. Its earlier mapping to real-time was previously reported as a NetworkProcess crash in the logs (it was in practice a kernel-delivered SIGKILL, but WebKit doesn't make any distinction while logging). After limits were adjusted, this thread was successfully demoted, and now that the mapping has changed, this is no longer promoted to real-time to begin with.

Finally, logging around portal-related failures has been updated to reduce noise.

Implemented the connectedMoveCallback() for custom elements to react to moveBefore().

Implemented the scaffolding for the moveBefore() DOM function. This is the first step towards implementing the full feature and is currently behind a runtime feature flag.

The Web Inspector now highlights the layout root element by hovering over a Layout event in the “Layout & Rendering” timeline view and reveals it in the element tree by clicking a little “go to” arrow button.

WebKitGTK 2.52.2 and WPE WebKit 2.52.2 have been released, which include a number of fixes. In particular, building for some less tested configurations should now be possible, and the WPE port includes fixes for input event handling in the Qt API bindings.

The releases were quickly followed by WebKitGTK 2.52.3 and WPE WebKit 2.52.3, with further fixes including an important patch for crashes in JavaScriptCore on architectures other than x86_64, support for the scrollbar-color CSS property, and a fix for rendering certain emoji glyphs. Additionally, the WPE port also gained a new setting to disable overlay scroll bars and use always-visible ones, fixed focus handling for touch input in the built-in Wayland platform implementation, and a build fix for the Qt one.

In addition to maintenance for the stable branch, the first unstable releases for the current development cycle are also available: WebKitGTK 2.53.1 and WPE WebKit 2.53.1. These are the first published versions that remove the option to use Cairo for 2D rendering—only Skia will be supported going forward. On the additions front, there are graphics subsystem improvements, a few API additions, and initial support in the CMake build system for builds using Profile-Guided Optimization (PGO, needs Clang for now). The goal of development releases is to gather early feedback on upcoming changes, and issue reports are welcome in Bugzilla.

PGO (Profile-Guided Optimization) builds with Clang are now supported by the CMake build system.