如何在Objective C中存储块？

我开始在目标C中编写一个简单的JSON RPC TCP库。我有一个调用RPC方法的方法：

- (void)invokeMethod:(NSString *)method
      withParameters:(id)parameters
           requestId:(id)requestId
             success:(void (^)(id responseObject))success
             failure:(void (^)(NSError *error))failure
{
    NSAssert(NSClassFromString(@"NSJSONSerialization"), @"NSJSONSerialization not found!");
    NSDictionary *requestObject = @{@"jsonrpc": @"2.0",
                                    @"method": method,
                                    @"params": parameters,
                                    @"id": requestId};
    NSError *error = nil;
    NSData *jsondData = [NSJSONSerialization dataWithJSONObject:requestObject options:0 error:&error];
    if (error){
        return failure(error);
    }
    [self->callbacks setObject:@{@"success": success ? [success copy] : [NSNull null],
                                 @"failure": failure ? [failure copy] : [NSNull null]}
                        forKey:requestId];
    NSString *str = [[NSString alloc] initWithData:jsondData encoding:NSUTF8StringEncoding];
    NSLog(@"Sending: %@", str);
    [self.socket writeData:jsondData withTimeout:-1 tag:1];
}

该类基本上表示一个TCP连接，当调用上述方法时，JSON数据将以id的形式通过TCP发送到服务器，该服务器将返回成功或失败：

- (void) socket:(GCDAsyncSocket *)sender didReadData:(NSData *)data withTag:(long)tag
{
    NSError *error = nil;
    [self.socket readDataWithTimeout:-1 tag:2];
    // … rpc response parsing code here, removed for simplicity …
    // detect if error or success
    NSDictionary *cbs = [self->callbacks objectForKey:JSONRPCObjectId];
    void(^success)(id resultObject) = [cbs objectForKey:@"success"];
    success ? success(JSONRPCObjectResult) : nil;
    return;
}

现在，我不确定如何跟踪successandfailure块，当前我将它们NSMutableDict使用requestId作为键存储在中。这样做是否合适，还是应该使用更好的方法？