Synchronization and concurrency
Deadlock (and avoiding it)
Java 5: ConcurrentHashMap
The Atomic classes in Java 5
In our outline of how synchronization works,
we saw that under the hood, a machine instruction generally called Compare-And-Swap (CAS)
was used to effectively read and write to a memory location at the same time. From Java 5 onwards,
CAS and related instructions are effectively exposed at the level of the Java programmer in the form of a
series of "atomic" classes in the java.util.concurrent package:
- Classes providing atomic access to main primitive types or to an object
reference: AtomicBoolean, AtomicInteger and AtomicLong, AtomicReference;
- Classes providing atomic access to fields in arrays of the correspoding types: AtomicIntegerArray,
- Classes to atomically couple a boolean or integer with a reference field:
AtomicMarkableReference and AtomicStampedReference;
- Atomic field updaters: classes to wrap up atomic access, via reflection, to volatile fields of another
class (AtomicIntegerFieldUpdater, AtomicLongFieldUpdater and
- Concurrent collection classes, including significantly
a highly concurrent hash map
Article written by Neil Coffey (@BitterCoffey).
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