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Performance New
This folder contains the code for the new performance panel that is a simplified recorder that works to record a performance profile, and inject it into profiler.firefox.com. This tool is not in charge of any of the analysis, only the recording.
TypeScript
This project contains TypeScript types in JSDoc comments. To run the type checker point your terminal to this directory, and run yarn install, then yarn test. In addition type hints should work if your editor is configured to speak TypeScript.
Overall Architecture
This project has a few different views explained below.
DevTools
This is a simplified recording panel that includes a preset dropdown. It's embedded in the DevTools. It's not the preferred way to use the profiler, but is included so that users are comfortable with existing workflows. This is built using React/Redux. The store's code is shared by all the views, but each view initializes it separately. The popup does not use React/Redux (explained later). When editing a custom preset, it takes you to "about:profiling" in a new tab.
This panel works similarly to the other DevTools panels. The devtools/client/performance-new/panel/initializer.js is in charge of initializing the page specifically for the DevTools workflow. This script creates a PerfActor that is then used for talking to the Gecko Profiler component.
DevTools Remote
This is the same UI and codebase as the DevTools panel, but it's accessible from about:debugging for remote targets. It uses the PerfFront for a remote target to profile on the remote device. When editing a custom preset, it takes you to "about:profiling" in the same modal.
This page is initialized with the PerfActor, but it will target a remote debuggee, like an Android Phone.
about:profiling
This view uses React/Redux for the UI, and is a full page for configuring the profiler. There are no controls for recording a profile, only editing the settings. It shares the same Redux store code as DevTools (instantiated separately), but uses different React components.
about:profiling Remote
This is the remote view of the about:profiling page. It is embedded in the about:debugging profiler modal dialog, and it is initialized by about:debugging. It uses preferences that are postfixed with ".remote", so that a second set of preferences are shared for how remote profiling is configured.
Profiler Popup
The popup is enabled by default on Nightly and Dev Edition, but it's not added to the navbar. Once the profiler menu button is added to the navbar, or other places in the UI, the shortcuts for the profiler will work. In any release channel the popup can be enabled by visiting profiler.firefox.com and clicking Enable Profiler Menu Button. This flips the pref "devtools.performance.popup.feature-flag" and the profiler button will always be available in the list of buttons for the Firefox UI.
The popup UI is not a React Redux app, but has a vanilla browser chrome implementation. This was done to make the popup as fast as possible, with a trade-off of some complexity with dealing with the non-standard (i.e. not a normal webpage) browser chrome environment. The popup is designed to be as low overhead as possible in order to get the cleanest performance profiles. Special care must be taken to not impact browser startup times when working with this implementation, as it also turns on the global profiler shortcuts.
Some code about the popup is also present in devtools/startup/DevToolsStartup.sys.mjs, and its markup is defined in browser/base/content/appmenu-viewcache.inc.xhtml (search for PanelUI-profiler).
Injecting profiles into profiler.firefox.com
After a profile has been collected, it needs to be sent to profiler.firefox.com for analysis. This is done by using browser APIs to open a new tab, and then setting up a web channel for the communication between the unprivileged page and the privileged chrome code. The page requests the profile data (as well as symbolication requests in some cases) through this Web Channel.
See handleWebChannelMessage in background.sys.mjs as well as related code in devtools/startup/DevToolsStartup.sys.mjs for implementation details. Both the DevTools Panel and the Popup use this channel.