1923493 - Make `backgroundupdate` task ignore update mutex/other instances updating when JS debugger is connected

Status: NEW

(Toolkit :: Application Update, enhancement, P3)

Description

[Nick Alexander :nalexander [he/him] (PTO August 1-10)]

Yesterday I was trying to debug the backgroundupdate task with the JS debugger (on Windows). Bug 1794051 worked like a charm... right up until the Update Service (correctly) reports that other instances are updating Firefox, which can happen when the Browser Toolbox process wins the race to take the update mutex first.

This ticket tracks doing something to https://searchfox.org/mozilla-central/rev/488d81581a9142d532bf814efa60564ff11599ca/toolkit/mozapps/update/UpdateService.sys.mjs#4007-4009 (or friends of that function) to allow the backgroundupdate task to avoid being blocked while debugging. For future me: stealing the "wrong" update lock from within UpdateService.sys.mjs, like:

gUpdateMutexHandle = createMutex(getPerInstallationMutexName(true) + "1", false);

avoids barrier 1, and the following avoids barrier 2:

Cc["@mozilla.org/updates/update-sync-manager;1"].getService(Ci.nsIUpdateSyncManager).resetLock(Services.dirsvc.get("ProfD", Ci.nsIFile));