How was the problem of re-executing side effects solved?

The problem of re-executing side effects in Java often arises in the context of multithreaded programming or when using transactions and asynchronous calls. Several approaches are used to solve it:

• Idempotency of operations: designing side effects so that repeated calls do not change the system's state (for example, updating a value by key rather than incrementing).

• Using atomic operations and synchronization: using synchronized, Lock, Atomic classes from java.util.concurrent to prevent re-execution or race conditions.

• Transactional management: within transactions (for example, using Spring Transaction Management), side effects are rolled back on errors, preventing re-application.

• Deduplication mechanisms: for example, storing unique request identifiers and checking before executing a side effect.

Example of an idempotent operation using ConcurrentHashMap:

ConcurrentHashMap<String, Boolean> processedRequests = new ConcurrentHashMap<>();

public void processRequest(String requestId) {
    if (processedRequests.putIfAbsent(requestId, true) == null) {
        // Perform side effect only if the request has not been processed
        performSideEffect();
    }
}