Shutdown

Profile Destruction

See shutdown.md

Browser Process Shutdown

BrowserProcess is also refcounted, much like Profile. ScopedKeepAlive inhibits teardown, and the refcount is managed by KeepAliveRegistry.

Stopping the UI Message Loop

• A UI event is received that leads to ~ScopedKeepAlive (closing the window, closing the last tab, keyboard shortcut for app termination, etc).
• If the refcount in KeepAliveRegistry drops to zero, then we begin application termination.
  • Note that macOS keeps the application alive even without browser windows by adding an extra ScopedKeepAlive in AppController.
• If the refcount reaches zero, post a task to the message loop to exit
• Notification content::NOTIFICATION_APP_TERMINATING is broadcast
• The UI message loop eventually stops running, we exit out of RunUIMessageLoop(). Note that all other main browser threads are still running their message loops. So even though the main (UI) thread outlives all other joined browser threads, its MessageLoop terminates first.

BrowserProcessImpl deletion

• After exiting the UI message loop, the shutdown sequence is started in BrowserMainParts::RunMainMessageLoopParts, which calls PostMainMessageLoopRun.
• In ChromeBrowserMainParts::PostMainMessageLoopRun:
  • The ProcessSingleton is released.
  • MetricsService (which records UMA metrics) is stopped, which:
    • Creates a log (for future upload) of all remaining metrics.
    • Records a successful shutdown.
    • The persistent metrics file, on disk, remains in case other metrics are updated after this point. Any such values will be sent during the next run sometime after Browser startup.
  • We persist Local State to disk.
  • We delete g_browser_process, which:
    • Deletes the ProfileManager (which deletes all the profiles and persists their state, such as Preferences)
    • Joins the watchdog, IO, CACHE, PROCESS_LAUNCHER threads, in that order
    • Shuts down the DownloadFileManager and SaveFileManager
    • Joins the FILE thread
    • Deletes the ResourceDispatcherHost which joins the WEBKIT thread
    • Joins the DB thread

ContentMain() exit

• The AtExitManager goes out of scope and destroys all Singletons/LazyInstances

Renderer Process Shutdown

Browser process triggers shutdown via:

• Closing a tab (explain the sequence of events from UI thread objects to the IO thread termination of a renderer process)