Java Concurrency: Threads, ExecutorService, Futures, and Synchronization

Java Concurrency

Concurrency is essential for scalable backend applications, but it introduces complexity and correctness risks.

Threads, Runnable, Callable

• A Thread represents an execution path.
• Implement Runnable for tasks without results.
• Implement Callable<V> for tasks that return values.

ExecutorService

• Use ExecutorService to manage thread pools and task execution.
• Avoid manually creating threads in service code.

Future and CompletableFuture

• Future represents an asynchronous computation result.
• CompletableFuture supports chaining, composition, and non-blocking callbacks.

Synchronization and volatile

• Use synchronized to protect shared mutable state.
• Use volatile for visibility of simple shared variables.
• Prefer higher-level concurrent constructs over manual locking when possible.

Atomic Classes and Locks

• Use AtomicInteger, AtomicLong, and other atomics for lock-free updates.
• Use Lock and ReentrantLock when explicit locking control is needed.

Thread Pool Patterns

• Use fixed or cached thread pools depending on workload.
• Configure pool size based on CPU and blocking behavior.
• Avoid unbounded thread pools in production.