This patch refactors the nsThread event queue to clean it up and to make it easier to restructure. The fundamental concepts are as follows:
Each nsThread will have a pointer to a refcounted SynchronizedEventQueue. A SynchronizedEQ takes care of doing the locking and condition variable work when posting and popping events. For the actual storage of events, it delegates to an AbstractEventQueue data structure. It keeps a UniquePtr to the AbstractEventQueue that it uses for storage.
Both SynchronizedEQ and AbstractEventQueue are abstract classes. There is only one concrete implementation of SynchronizedEQ in this patch, which is called ThreadEventQueue. ThreadEventQueue uses locks and condition variables to post and pop events the same way nsThread does. It also encapsulates the functionality that DOM workers need to implement their special event loops (PushEventQueue and PopEventQueue). In later Quantum DOM work, I plan to have another SynchronizedEQ implementation for the main thread, called SchedulerEventQueue. It will have special code for the cooperatively scheduling threads in Quantum DOM.
There are two concrete implementations of AbstractEventQueue in this patch: EventQueue and PrioritizedEventQueue. EventQueue replaces the old nsEventQueue. The other AbstractEventQueue implementation is PrioritizedEventQueue, which uses multiple queues for different event priorities.
The final major piece here is ThreadEventTarget, which splits some of the code for posting events out of nsThread. Eventually, my plan is for multiple cooperatively scheduled nsThreads to be able to share a ThreadEventTarget. In this patch, though, each nsThread has its own ThreadEventTarget. The class's purpose is just to collect some related code together.
One final note: I tried to avoid virtual dispatch overhead as much as possible. Calls to SynchronizedEQ methods do use virtual dispatch, since I plan to use different implementations for different threads with Quantum DOM. But all the calls to EventQueue methods should be non-virtual. Although the methods are declared virtual, all the classes used are final and the concrete classes involved should all be known through templatization.
MozReview-Commit-ID: 9Evtr9oIJvx
This parameter isn't used by any implementation of onDispatchedEvent,
and keeping the parameter makes later refactorings in this bug more difficult.
MozReview-Commit-ID: 90VY2vYtwCW
We want people to transition to using event targets rather than threads when possible. These
getters should make it easier to make that change.
MozReview-Commit-ID: 3bN4tRgJjBL
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
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
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.
