It also removes LiveDOMReferences destructor that it's a no-op but it contains an assert that was being violated causing an endless cycle of destructor calls ending up in a stack overflow.
This used to conflict with the util crate from the standard library, which
has long since been removed.
The import in layout has not been changed because of a conflict with the
util mod there.
It is possible for a PaintTask to start exiting soon after sending new
buffers to the compositor. In that case, the compositor should return
the now unnecessary buffers to the PaintTask so that it can properly
free them.
To accomplish this, the compositor now keeps a hash map of paint task
channels per pipeline id. When a PaintTask exists, the constellation
informs the compositor that it can forget about it. Additionally, the
PaintTask should not wait for any buffers when the engine is doing a
complete shutdown. In that case, the compositor is already halted and
has simply let all buffers leak. We pipe through the shutdown type when
destroying the pipeline to make this decision.
Fixes#2641.
This replaces the specialized TrustedXHRAddress and TrustedWorkerAddress code that was used for the same purpose. A non-zero refcount pins the given DOM object's reflector and prevents it from being GCed even when there are no other outstanding references visible to SpiderMonkey. This will enable us to implement asynchronous operations that refer to particular DOM objects (such as "queue a task to fire a simple event named load at the iframe element" from the spec) safely and conveniently, and paves the way for things like asynchronous network responses.
Some concerns about the resulting size of XHR progress messages have been expressed, but I believe optimizations to reduce that can be implemented in subsequent PRs.
r? @Ms2ger - note in particular the changes to the worker lifetime code. I couldn't figure out how to achieve an identical lifetime to the previous addref/release pairing, and I also was having trouble figuring out why the existing setup was safe. The new implementation now holds the main script task Worker object alive via the TrustedWorkerAddress field in the dedicated worker global scope, which is a significant difference.
This refs #3735. As discussed in the issue, I did it cloning when I couldn't dereference an attribute. The trait method should be on `&self` for object-safety reasons.
