This also fixes a bug where task IDs were being deallocated from the
wrong IDAllocator. I don't know if it was actually possible to cause any
real trouble with that mistake, nor do I know how to write a test for
it, but this makes the bug go away.
Changes the signature of queue_fetch_task() from AK:Function to
JS::HeapFunction to be more clear to the user of the function that this
is what it uses internally.
...and use HeapFunction instead of SafeFunction for task steps.
Since there is only one EventLoop per process, it lives as a global
handle in the VM custom data.
This makes it much easier to reason about lifetimes of tasks, task
steps, and random stuff captured by them.
The HTMLMediaElement, for example, contains spec text which states any
ongoing fetch process must be "stopped". The spec does not indicate how
to do this, so our implementation is rather ad-hoc.
Our current implementation may cause a crash in places that assume one
of the fetch algorithms that we set to null is *not* null. For example:
if (fetch_params.process_response) {
queue_fetch_task([]() {
fetch_params.process_response();
};
}
If the fetch process is stopped after queuing the fetch task, but not
before the fetch task is run, we will crash when running this fetch
algorithm.
We now track queued fetch tasks on the fetch controller. When the fetch
process is stopped, we cancel any such pending task.
It is a little bit awkward maintaining a fetch task ID. Ideally, we
could use the underlying task ID throughout. But we do not have access
to the underlying task nor its ID when the task is running, at which
point we need some ID to remove from the pending task list.
