In this chapter, we showed how to create and start threads, and wait for their termination. We have shown how to achieve inter-thread communication by modifying the shared memory and by using the synchronized statement, and what it means for a thread to be in a blocked state. We have studied approaches to prevent deadlocks by imposing ordering on the locks and avoided busy-waits in place of guarded blocks. We have seen how to implement a graceful shutdown for thread termination and when to communicate using volatiles. We witnessed how the correctness of a program can be compromised by undesired interactions known as race conditions as well as data races due to the lack of synchronization. And, most importantly, we have learned that the only way to correctly reason about the semantics of a multithreaded program is in terms of happens-before relationships defined by the JMM.

The language primitives and APIs presented in this section are low-level; they are the basic building blocks...