The Java Memory Model - Java Concurrency in Practice - page 395

Volatile variable rule. A write to a volatile field happens-before every subsequent read of
that same field. [4]

Thread start rule. A call to Thread.start on a thread happens-before every action in the star-
ted thread.

Thread termination rule. Any action in a thread happens-before any other thread detects
that

thread has terminated, either by successfully return from Thread.join or by

Thread.isAlive returning false.

Interruption rule. A thread calling interrupt on another thread happens-before the interrup-
ted thread detects the interrupt (either by having InterruptedException thrown, or invoking
isInterrupted or interrupted).

Finalizer rule. The end of a constructor for an object happens-before the start of the finalizer
for that object.

Transitivity. If A happens-before B, and B happens-before C, then A happens-before C .

Even though actions are only partially ordered, synchronization actions—lock acquisition
and release, and reads and writes of volatile variables—are totally ordered. This makes it
sensible to describe happens-before in terms of “subsequent” lock acquisitions and reads of
volatile variables.

Figure 16.2 . illustrates the happens-before relation when two threads synchronize using a
common lock. All the actions within thread A are ordered by the program order rule, as are
the actions within thread B. Because A releases lock M and B subsequently acquires M, all
the actions in A before releasing the lock are therefore ordered before the actions in B after
acquiring the lock. When two threads synchronize on different locks, we can't say anything
about the ordering of actions between them—there is no happens-before relation between the
actions in the two threads.