Unfortunately course designed very poorly.
While lectures generally are good, there are not enough of materials. I'm sorry to say, but programming assignments are bad. Forum is full of posts like "Grader grades the same file for 100 and 50 points". Teaching stuff reacts on this like, quote:
"Hi Anton, I may have missed it but I don't see a question in your text? Is there something I can help with?"
Yes, dear teaching stuff, you can help not only Anton, but all of us. Take a look at Parallel Programming Using Scala, here, on Coursera. Their grader is stable, and apparently there is a well-known, common way of reaching the stable state of JVM using testing frameworks. They measure performance after stable state is reached.
Also, it is not clear what is actually the topic of this course? Parallel programming? No. There is almost nothing to do with common parallel programming. No info about hardware, schedulers, operating systems, JVM. Java? Also no, there is no information on language, its specific parts, its implementation for threads, no words are said about JVM, actually JVM event wasn't mentioned. So, then, what is this course about? I may say this course "A good introduction to parallel programming".
I hope the next course in this specialization will get much better.