Atomic, Volatile, or Synchronized: Which Guarantees Thread Safety?

Difference Between Atomic, Volatile, and Synchronized

Internal Workings

No Synchronization:

• The variable is accessed without any form of synchronization.
• It is prone to race conditions and visibility issues.

AtomicInteger:

• Uses CAS (Compare-and-Swap) operations to atomically modify a variable.
• It involves a loop that checks if the current value is the same as the expected value before updating it.

Volatile:

• Ensures visibility of variable changes across threads.
• It does not prevent race conditions and requires explicit synchronization for thread safety.

Code Comparisons

Code 1: Not thread-safe due to pre/post-increment operation not being atomic.

Code 2: Thread-safe because AtomicInteger uses CAS to ensure atomic increment.

Code 3: Not thread-safe because volatile only ensures visibility but does not prevent race conditions.

Volatile vs Synchronized Behavior

Volatile without Synchronization:

• Guarantees visibility of changes, but not thread safety.
• Race conditions can occur if multiple threads attempt to modify the variable simultaneously.

Multiple Independent Synchronized Blocks:

• Incorrect for synchronization because it uses a different lock object for each synchronized block.
• No protection against race conditions.

Local Variable Copies

In multi-threaded environments, each thread maintains its own local copy of variables. This occurs to improve performance by reducing memory contention. However, it can lead to inconsistency if the local copies are not synchronized with the main memory or other threads' local copies.

Thread Safety

• Atomic variables like AtomicInteger are thread-safe by design.
• Synchronized methods or blocks can be used to make non-atomic variables thread-safe by ensuring that only one thread executes the critical section at a time.

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