How can server function calls be limited or prevented from being repeated?

To limit or prevent repeated calls to server functions, several approaches can be used:

1. Idempotency: design functions so that repeated calls with the same parameters do not alter the system state further.
2. Tokens or unique request identifiers: the client sends a unique ID with the request, and the server checks whether this request has already been processed.
3. Server-level locking: upon receiving a request, the server places a lock to prevent processing duplicate calls simultaneously.
4. Caching results: if the function computes a result, it can be stored and returned on subsequent calls with the same parameters.

An example of using a unique token in Java (simplified):

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

public Response handleRequest(Request req) {
    if (processedRequests.putIfAbsent(req.getId(), true) != null) {
        return new Response("Duplicate request");
    }
    // process the request
}