[#issue-469] -fsm-trigger depends on state consistency

[scgilardi]

• re: Reaching invalid state by dispatching continuosly #469
• -fsm-trigger reads from and writes to volatile state
• it works fine in cljs because that's single-threaded
• jvm clojure interop creates a single threaded executor, but that
  coexists with the main thread for a total thread count of 2
• adding locking on the EventQueue object avoids the race for
  clojure and is a no-op for clojurescript.

[danielcompton]

Thanks heaps for this, we really appreciate it (and your previous work on re-frame 😄).

[scgilardi]

You're welcome! :)

And thanks for the test!

In running the test, I did notice that it needs a bit of a tweak. The test doesn't currently wait for the processing of the events to be complete before checking that they all got processed. Maybe add a "reached the end" (sentinel) event to the queue after the test events and write some code that detects when that one is processed (maybe an event callback), or maybe just poll the db (in the test) for a count on the array until it gets to 1000 and fail if that doesn't happen in a couple of seconds. Something idiomatic and effective. As it is now, the test passes only intermittently.