Question

Hey all, I’m working on some code I inherited, it looks like one thread is setting a boolean member variable while another thread is in a while loop checking it. Will this actually work OK or should I change it to use synchronized getters or setters on the boolean var?

Answer 1

In the case of reading and writing a primitive like bool or int declaring them as volatile will be plenty. When one threads read the other thread would have finished writing. The variable will never be in an invalid state.

It’s probably fair to say that on the whole, the volatile keyword in
Java is poorly documented, poorly understood, and rarely used. To make
matters worse, its formal definition actually changed as of Java 5.
Essentially, volatile is used to indicate that a variable’s value will
be modified by different threads.

Declaring a volatile Java variable means:

1. The value of this variable will
   never be cached thread-locally: all
   reads and writes will go straight to
   “main memory”;
2. Access to the variable acts as
   though it is enclosed in a
   synchronized block, synchronized on
   itself.

We say “acts as though” in the second point, because to the programmer
at least (and probably in most JVM implementations) there is no actual
lock object involved.

http://www.javamex.com/tutorials/synchronization_volatile.shtml