Previously an UnhandledException would be thrown and the stack trace / message would be printed to System.err in the default UncaughtExceptionHandler for ThreadGroup. This was undesirable as it meant that logging frameworks / exception monitors such as Sentry were unable to get the exception. Additionally it would cause the death of the thread in the ExecutorService. This change mimics the behaviour of exceptions occuring during synchronous tasks.
In some situations, an async task could be cancelled with no tasks
pending. This means the finally {} block from run() never gets executed
properly on the last async task to have run, as it expected to be
executed again.
This fix takes the only spot that the task period is set to cancelled
and will check to see if the task should be purged from the runners
list.
The new scheduler uses a non-blocking methodology. Combining volatile
references to make a linked reference chain, with the atomic reference
handling the tail, tasks are queued without waiting for locks. The main
thread will no longer limit the length of time spend for scheduled tasks,
but no task will run twice in the same tick. Scheduling a new task inside of
a synchronous task will always run the new task during the same tick,
assuming there is no supplied delay > 0.
Asynchronous tasks are now run using a thread pool. Any thread-local
implemenation should now account for threads being reused between
executions.
Race conditions were carefully examined and the order of logic is now very
important. Each task is placed in a secondary collection before removal from
primary collections. Thus, by reading tasks from the collections in the same
order they travel, it retains state-safety. This does make modifications
less responsive in some situations, as the task may be transitioning before
the modifier accesses it. This cost outweighs the requirement to synchronize
on the scheduler; previously any conflict would be first-come-first-serve,
with the main thread backing out arbitrarily.
