#include #include #include void updateBalance(redisContext* context, int user_id, int increment) { while (true) { redisReply* reply; // WATCH command reply = (redisReply*)redisCommand(context, "WATCH balance:%d", user_id); freeReplyObject(reply); // Get current balance reply = (redisReply*)redisCommand(context, "GET balance:%d", user_id); int balance = (reply->type == REDIS_REPLY_NIL) ? 0 : std::stoi(reply->str); freeReplyObject(reply); // MULTI command to start a transaction reply = (redisReply*)redisCommand(context, "MULTI"); freeReplyObject(reply); // Set new balance reply = (redisReply*)redisCommand(context, "SET balance:%d %d", user_id, balance + increment); freeReplyObject(reply); // EXEC command to execute transaction reply = (redisReply*)redisCommand(context, "EXEC"); if (reply->type == REDIS_REPLY_ARRAY && reply->elements == 1) { freeReplyObject(reply); break; // Transaction succeeded } std::cerr << "Retrying transaction due to an external modification." << std::endl; freeReplyObject(reply); } } int main() { // Connect to the Redis server redisContext* context = redisConnect("127.0.0.1", 6379); if (context == nullptr || context->err) { if (context) { std::cerr << "Connection error: " << context->errstr << std::endl; } else { std::cerr << "Connection error: can't allocate Redis context" << std::endl; } return 1; } // Set initial balance for user 1 redisReply* reply = (redisReply*)redisCommand(context, "SET balance:1 100"); freeReplyObject(reply); // Update balance for user 1 updateBalance(context, 1, 50); // Retrieve updated balance reply = (redisReply*)redisCommand(context, "GET balance:1"); if (reply->type == REDIS_REPLY_STRING) { std::cout << "Updated balance for user 1: " << reply->str << std::endl; } else { std::cerr << "Failed to retrieve the updated balance." << std::endl; } freeReplyObject(reply); // Free the context redisFree(context); return 0; }