Instead of having an annoying loop that constantly reschedules a
Core::EventLoop trigger, have the ALooperEventLoopManager do it itself
in the did_post_event() function.
We cannot simply re-use the Unix implementation directly because that
implementation expects to actually be called all the time in order to
service timers. If you don't call its' pump() method, timers do not get
triggered. So, we do still need the seconary thread for Timers that was
added earlier.
The FIXME at the bottom of Timer.nativeRun was on the money, and was
the cause of some leaked timers. Solve the issue by passing the
EventLoopImplementation to the JVM Timer object and retrieving it's
thread_local timer list, and posting the events to the Impl rather than
trying to invoke the receiver's timer event callback directly in
the Timer thread. Because the implementation of
ALooperEventLoopManager::did_post_event() reaches for
EventLoop::current(), we also need to make sure that the timer thread
acutally *has* an EventLoop, even if we don't expect to use it for
anything. And we need to make sure to pump it to clear out any of the
poke() invocations sending 4 bytes to the wake pipe for that thread.
Timers run in their own thread, to take advantage of existing Java
Executor features. By hooking into ALooper, we can spin the main
Activity's UI thread event loop without causing a fuss, or spinning the
CPU by just polling our event loop constantly.
