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Java: volatile boolean vs AtomicBoolean
When is it appropriate to use a volatile primitive (e.g. boolean, integer or long) instead of AtomicBoolean, AtomicInteger or AtomicLong, and vice-versa?
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Volatile and Atomic are two different concepts. Volatile ensures, that a certain, expected (memory) state is true across different threads, while Atomics ensure that operation on variables are performed atomically.
Synchronized Vs Atomic Vs Volatile:Volatile and Atomic is apply only on variable , While Synchronized apply on method. Volatile ensure about visibility not atomicity/consistency of object , While other both ensure about visibility and atomicity.
Atomic variables in Java provide the same memory semantics as a volatile variable, but with an added feature of making non-atomic operation atomic. It provides a method to perform atomic increment, decrement, compare-and-swap (CAS) operations.
The visibility semantics are exactly the same, the situation where using the atomic primitives is useful is when you need to use their atomic methods.
For example:
if (volatileBoolean) {
volatileBoolean = !volatileBoolean;
}
could create issues in a multi threaded environment as the variable could change between the two lines. If you need the test&assignment to be atomic, you can use:
atomicBoolean.compareAndSet(true, false);
Using a plain volatile is simpler and more efficient if all you want to do is set or get the value. (But not get&set the value)
If you want more operations like getAndIncrement or compareAndSwap you need to use the AtomicXxxx classes.
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