The intent of idleDispatch is the possibility to have a runnable
executed when the thread is idle. This is accomplished by adding an
event queue for idle tasks that will only be considered when the main
event queue is empty and the caller of ProcessNextEvent doesn't
require that we wait until there is an event on the main event queue.
MozReview-Commit-ID: IDWQfzZqWpZ
--HG--
extra : rebase_source : 0d5bfeebd08e01597c2cd8b76e8e848d9f9c58f0
The intent of idleDispatch is the possibility to have a runnable
executed when the thread is idle. This is accomplished by adding an
event queue for idle tasks that will only be considered when the main
event queue is empty and the caller of ProcessNextEvent doesn't
require that we wait until there is an event on the main event queue.
MozReview-Commit-ID: IDWQfzZqWpZ
--HG--
extra : rebase_source : b16ff65d7a9b2fa16216a9ce8756358014d7ad96
The new name makes the sense of the condition much clearer. E.g. compare:
NS_WARN_IF_FALSE(!rv.Failed());
with:
NS_WARNING_ASSERTION(!rv.Failed());
The new name also makes it clearer that it only has effect in debug builds,
because that's standard for assertions.
--HG--
extra : rebase_source : 886e57a9e433e0cb6ed635cc075b34b7ebf81853
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.
Andreas Farre
Carsten "Tomcat" Book
Eric Faust
Wes Kocher
Phil Ringnalda
Nicholas Nethercote
Xidorn Quan
Kyle Huey
Eric Rahm
Birunthan Mohanathas
Randell Jesup
Randall Barker
Ben Turner
Ehsan Akhgari
Olli Pettay
Benjamin Smedberg
Joshua Cranmer
Julian Seward
Ryan VanderMeulen
Chris Peterson
Isaac Aggrey