This is motivated by three separate but related problems:
1. Our concept of recursion depth is broken for things that run from AfterProcessNextEvent observers (e.g. Promises). We decrement the recursionDepth counter before firing observers, so a Promise callback running at the lowest event loop depth has a recursion depth of 0 (whereas a regular nsIRunnable would be 1). This is a problem because it's impossible to distinguish a Promise running after a sync XHR's onreadystatechange handler from a top-level event (since the former runs with depth 2 - 1 = 1, and the latter runs with just 1).
2. The nsIThreadObserver mechanism that is used by a lot of code to run "after" the current event is a poor fit for anything that runs script. First, the order the observers fire in is the order they were added, not anything fixed by spec. Additionally, running script can cause the event loop to spin, which is a big source of pain here (bholley has some nasty bug caused by this).
3. We run Promises from different points in the code for workers and main thread. The latter runs from XPConnect's nsIThreadObserver callbacks, while the former runs from a hardcoded call to run Promises in the worker event loop. What workers do is particularly problematic because it means we can't get the right recursion depth no matter what we do to nsThread.
The solve this, this patch does the following:
1. Consolidate some handling of microtasks and all handling of stable state from appshell and WorkerPrivate into CycleCollectedJSRuntime.
2. Make the recursionDepth counter only available to CycleCollectedJSRuntime (and its consumers) and remove it from the nsIThreadInternal and nsIThreadObserver APIs.
3. Adjust the recursionDepth counter so that microtasks run with the recursionDepth of the task they are associated with.
4. Introduce the concept of metastable state to replace appshell's RunBeforeNextEvent. Metastable state is reached after every microtask or task is completed. This provides the semantics that bent and I want for IndexedDB, where transactions autocommit at the end of a microtask and do not "spill" from one microtask into a subsequent microtask. This differs from appshell's RunBeforeNextEvent in two ways:
a) It fires between microtasks, which was the motivation for starting this.
b) It no longer ensures that we're at the same event loop depth in the native event queue. bent decided we don't care about this.
5. Reorder stable state to happen after microtasks such as Promises, per HTML. Right now we call the regular thread observers, including appshell, before the main thread observer (XPConnect), so stable state tasks happen before microtasks.
For certain tests, the AndroidBridge is not initialized, but some GeckoAppShell functions are still called indirectly. For now, this patch adds checks to skip these calls if there's no AndroidBridge. However, in the future, most of the affected code should be refactored to not require these checks.
The ipc/chromium/src/base/ changes here (except those mentioned below)
are the majority of the base/ changes (excluding those that patch code
that does not exist yet in our copy) in:
> From: jar@chromium.org <jar@chromium.org@0039d316-1c4b-4281-b951-d872f2087c98>
> Date: Sat, 6 Nov 2010 22:23:29 +0000 (+0000)
> Subject: Switch to using TimeTicks rather than Time in message loops
> X-Git-Url: http://git.chromium.org/gitweb/?p=chromium.git;a=commitdiff_plain;h=f592c218c18bd1f8308489aaef2e329244ced330
>
> Switch to using TimeTicks rather than Time in message loops
>
> Switch to using TimeTicks rather than Time so that we
> are not dependent on changes in the system clock.
>
> r=mbelshe,darin
> Review URL: http://codereview.chromium.org/3884001
>
> git-svn-id: svn://svn.chromium.org/chrome/trunk/src@65322 0039d316-1c4b-4281-b951-d872f2087c98
The ipc/glue changes, and the message_pump_android.* and
message_pump_qt.* changes in ipc/chromium/src/base/, change signatures
to match.
Kyle Huey
Wes Kocher
Kartikaya Gupta
Bill McCloskey
Jonathan Watt
Nathan Froyd
Jim Chen
Ryan VanderMeulen
Andrea Marchesini
Ehsan Akhgari
Jim Mathies
Ben Kelly
Birunthan Mohanathas
snigdha
Josh Aas
Ben Turner
Chris Kitching
Thinker Lee ext:(%2C%20Cervantes%20Yu%20%3Ccyu%40mozilla.com%3E)
Chris Kitching
Joshua Cranmer
Brian R. Bondy
Trevor Saunders
jar@chromium.org, L. David Baron
Brad Lassey
Chris Jones