author Kyle Huey <>
Tue, 11 Aug 2015 06:10:46 -0700
changeset 257246 a13c1f26e351dd6251da641fe7a9eb53790fc2d0
parent 1 9b2a99adc05e53cd4010de512f50118594756650
permissions -rw-r--r--
Bug 1179909: Refactor stable state handling. r=smaug 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.

Please be apprised of the following Legal Notices:

A) The U.S. District Court for the Eastern District of Virginia has
ruled that the Netscape Navigator code does not infringe Wang's U.S.
Patent No. 4,751,669 ("the '669 Patent") because: 1) HTML is not
Videotex as defined by the '669 patent; 2) web servers are not central
suppliers; and 3) Navigator does not "connect," as defined by the '669
Patent, to web servers on the Internet. Wang may appeal this decision to
the Federal Circuit. Wang contended that its Patent disclosing a
"Videotex" system, is infringed by the following functionality in the
Netscape Navigator code: 1) the animated logo and status line indicators
--See Claims 1,8 and 9; 2) the "File Save As" function --See Claims
23-27; 3) Bookmarks and Rename Bookmarks in the Properties window --See
Claims 20-22; 4) storing HTML, GIF, and JPEG files and adding filename
extensions --See Claim 38

B) Intermind owns pending U.S. patent applications on communications
systems which employ metadata ("channel objects") to define a control
structure for information transfer. The Netscape code does not infringe
as released; however, modifications which utilize channel objects as
described by Intermind should be considered carefully. The following is
a statement from Intermind: "Intermind's claims fundamentally involve
the use of a control structure to automate communications. ...The
essence of Intermind's top claim is that two devices sender and receiver
have persistent storage, communicate over a network, and exchange a
control structure including metadata which describes: 1) what
information is to be updated, 2) when to update this information, and 3)
how to transfer the updated information. In addition, at least the
receiving device must be able to process the metadata in order to
perform the update determination and transfer. Any digital
communications system which incorporates all of these elements will be
covered by Intermind's patents." See

C) Stac, Inc., and its licensing agent Hi/fn, own several patents which
disclose data compression methods implementing an LZS compression
algorithm, including U.S. Patent Nos. 4,701,745 and 5,016, 009 ("the
Stac Patents"). The Netscape Communicator code does not perform
compression. If you modify the Netscape source code to perform
compression, please take notice of the Stac Patents.

D) Netscape Communications Corporation ("Netscape") does not guarantee
that any source code or executable code available from the
domain is Year 2000 compliant.