I am unable to start Nightly for some time (weeks) and have accepted perhaps half a dozen updates in this time. Starting Nightly shows a white screen with no UI before the system prompts to kill the App. I finally attached my device and grabbed two logcats, which I will attach.

Further investigation reveals this to be a catastrophic failure during session restore. I'm not comfortable posting my sessionstore.js publicly, but I've emailed it to Sebastian and JanH.

What happens is that if the main thread arrives here (https://dxr.mozilla.org/mozilla-central/rev/b6f7d0eb61b1878d3d906bd231edf225463ece3f/mobile/android/base/java/org/mozilla/gecko/GeckoApp.java#1539) before the background thread has finished parsing the session data, it will never be released again even though the background thread is calling notifyAll() (https://dxr.mozilla.org/mozilla-central/rev/b6f7d0eb61b1878d3d906bd231edf225463ece3f/mobile/android/base/java/org/mozilla/gecko/GeckoApp.java#1304). The problem is that the session data parsing is running from within a Runnable, so the "this" there is not the same "this" as on the main thread, so notifyAll() naturally won't work.

If the main thread has to wait for the session data parsing to finish - which is more likely when you've got many tabs open, meaning a large sessionstore.js file - it does so on "this", i.e. GeckoApp. The session data parsing itself is done from within a Runnable, so we need to qualify "this" there if we want it to refer to GeckoApp itself, so we can successfully release any waiting threads through notifyAll(). Review commit: https://reviewboard.mozilla.org/r/59094/diff/#index_header See other reviews: https://reviewboard.mozilla.org/r/59094/

Comment on attachment 8762403 [details] Bug 1279273 - Use correct synchronization object for session data parsing. https://reviewboard.mozilla.org/r/59094/#review56230 Ah, nice!

Comment on attachment 8762403 [details] Bug 1279273 - Use correct synchronization object for session data parsing. Approval Request Comment [Feature/regressing bug #]: Mobile session restoring, bug 905223 [User impact if declined]: Firefox might hang during startup, especially for users with lots of open tabs. [Describe test coverage new/current, TreeHerder]: manual [Risks and why]: Low, this just ensures that waiting and notifying threads are actually using the same synchronization object. [String/UUID change made/needed]: none

Pushed by cbook@mozilla.com: https://hg.mozilla.org/integration/fx-team/rev/53f5b5c289fb Use correct synchronization object for session data parsing. r=sebastian

Comment on attachment 8762403 [details] Bug 1279273 - Use correct synchronization object for session data parsing. Recent regression in session store, we definitely want to fix this on aurora 49.