What Operations Are Atomic in Java?

Atomic Operations in Java

In Java, atomicity refers to operations that are indivisible as a single unit, ensuring that they complete in their entirety without being interrupted by another thread. This property is crucial for maintaining thread safety and avoiding data inconsistencies.

Atomic Operations:

• Assignments of primitive types (except long and double): Operations involving assignments to primitive data types (int, boolean, etc.), excluding long and double, are considered atomic.
• Assignments of references: Assignments to reference variables are atomic, ensuring that either a valid reference or null is assigned without intermediate states.
• Assignments of volatile variables: Assignments to volatile variables are atomic, providing visibility guarantees between threads. Volatile variables are specially marked to ensure immediate visibility of updates to other threads.
• Operations on java.concurrent.Atomic* classes: Classes such as AtomicBoolean, AtomicInteger, and AtomicLong provide atomic operations for manipulating primitive values. These classes guarantee atomic updates and visibility across threads.

Exceptions:

• Assignments of long and double: Operations involving long and double are not inherently atomic on all architectures. However, in practice, they may behave atomically on common 64-bit CPUs.
• Visibility of atomic operations: While atomicity ensures the integrity of operations within a thread, it does not imply visibility to other threads. Separate mechanisms, such as synchronization or volatile variables, are required to make updates visible to all threads.

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