Back / Forward Cache

by Chris Dumez

• Objectives
  • Make pages suspendable most of the time (~98%)
  • Allow for much faster back/forward navigation
  • Means addressing most failures to suspend, not introducing new ones
• ActiveDOMObject
  • Largest cause of failures
  • Need to drop all shouldPreventEnteringBackForwardCache_DEPRECATED() overrides
  • Queue tasks on the event loop for running script (e.g. event dispatch, promise resolution)
  • Pause CPU-intensive work (e.g. animations) in suspend() and unpause it in resume()
  • Abort work that cannot be paused in suspend() and make sure tasks to dispatch relevant error events are queued on the event loop
• Dedicated Workers
  • Dedicated workers have their whole thread suspended when entering the back/forward cache
  • ActiveDOMObject::suspend() / resume() do not get called
• Service Workers
  • Service workers cannot be easily suspended because they can be shared
  • When a client page goes into the back/forward cache, it gets disconnected as a client of the service worker
  • When a service worker no longer has any clients, it is terminated