Java中的原子布尔与同步布尔

Question

I've come across these two in some multi-threaded code and was wondering if there is if/any difference between the two.

I mean does the use of an AtomicBoolean, rather than a SynchronizedBoolean, make a significant difference in performance?

And does it affect the correctness of the computation?

Answer 1

AtomicBoolean is a part of the standard java concurrent package. SynchronizedBoolean is part of a set of utilities created by Doug Lea (author of much of the java concurrent packages). Performance-wise, you should expect AtomicBoolean to perform better -- it uses a volatile boolean whereas SynchronizedBoolean uses a ReadWriteLock.

However in practice for most applications you won't notice much difference.

The real difference (and what should guide your choice) is in the semantics the two classes offer. AtomicBoolean provides just simple set/get/compareAndSet operations. The SynchronizedBoolean offers atomic boolean operations and exposes its internal lock to allow you to execute Runnables within the context of its value.

Doug Lea has offered this source free to the community. I have found an extension to SynchronizedBoolean, WaitableBoolean particularly useful since it allows you to execute a Runnable within the lock whenever a particular state change occurs.