缓存结果来自 ASP.NET 中的异步方法
本文关键字:异步方法 NET ASP 结果 缓存 | 更新日期: 2023-09-27 18:32:53
我有一个简单的MVC控制器,我已经做了异步,它使用await Task.WhenAll从Web服务获取数据。我想缓存这些调用的结果,这样我就不必一直调用 API。目前,当我得到响应时,我正在视图控制器中缓存结果,但理想情况下,我希望我调用的方法(调用 API)来处理缓存。问题是该方法还无法访问结果,因为它是异步的,只返回一个任务。
是否有可能使用另一种方法在返回结果后缓存结果?
public async Task<ActionResult> Index()
{
// Get data asynchronously
var languagesTask = GetDataAsync<List<Language>>("languages");
var currenciesTask = GetDataAsync<List<Currency>>("currencies");
await Task.WhenAll(languagesTask, currenciesTask);
// Get results
List<Language> languages = languagesTask.Result;
List<Currency> currencies = currenciesTask.Result;
// Add results to cache
AddToCache("languages", languages);
AddToCache("currencies", currencies);
// Add results to view and return
ViewBag.languages = languages;
ViewBag.currencies = currencies;
return View();
}
public async Task<T> GetDataAsync<T>(string operation)
{
// Check cache for data first
string cacheName = operation;
var cacheData = HttpRuntime.Cache[cacheName];
if (cacheData != null)
{
return (T)cacheData;
}
// Get data from remote api
using (HttpClient client = new HttpClient())
{
client.BaseAddress = new Uri("https://myapi.com/");
var response = await client.GetAsync(operation);
// Add result to cache
//...
return (await response.Content.ReadAsAsync<T>());
}
}
只要缓存实现在内存中,就可以缓存任务本身而不是任务结果:
public Task<T> GetDataAsync<T>(string operation)
{
// Check cache for data first
var task = HttpRuntime.Cache[operation] as Task<T>;
if (task != null)
return task;
task = DoGetDataAsync(operation);
AddToCache(operation, task);
return task;
}
private async Task<T> DoGetDataAsync<T>(string operation)
{
// Get data from remote api
using (HttpClient client = new HttpClient())
{
client.BaseAddress = new Uri("https://myapi.com/");
var response = await client.GetAsync(operation);
return (await response.Content.ReadAsAsync<T>());
}
}
这种方法还有一个额外的好处,即如果多个HTTP请求尝试获取相同的数据,它们实际上将共享任务本身。因此,它共享实际的异步操作而不是结果。
但是,此方法的缺点是Task<T>
不可序列化,因此,如果您使用的是自定义磁盘支持的缓存或共享缓存(例如 Redis),则此方法将不起作用。
回答这个问题有点晚了,但我想我可以通过一个名为 LazyCache 的开源库来改进史蒂文斯的答案,它将在几行代码中为您完成此操作。它最近进行了更新,以处理这种情况在内存中缓存任务。它也在 nuget 上可用。
给定您的获取数据方法是这样的:
private async Task<T> DoGetDataAsync<T>(string operation)
{
// Get data from remote api
using (HttpClient client = new HttpClient())
{
client.BaseAddress = new Uri("https://myapi.com/");
var response = await client.GetAsync(operation);
return (await response.Content.ReadAsAsync<T>());
}
}
然后您的控制器变为
public async Task<ActionResult> Index()
{
// declare but don't execute a func unless we need to prime the cache
Func<Task<List<Language>>> languagesFunc =
() => GetDataAsync<List<Currency>>("currencies");
// get from the cache or execute the func and cache the result
var languagesTask = cache.GetOrAddAsync("languages", languagesFunc);
//same for currencies
Func<Task<List<Language>>> currenciesFunc =
() => GetDataAsync<List<Currency>>("currencies");
var currenciesTask = cache.GetOrAddAsync("currencies", currenciesFunc);
// await the responses from the cache (instant) or the api (slow)
await Task.WhenAll(languagesTask, currenciesTask);
// use the results
ViewBag.languages = languagesTask.Result;
ViewBag.currencies = currenciesTask.Result;
return View();
}
默认情况下,它具有内置锁定功能,因此可缓存方法每次缓存未命中只会执行一次,并且它使用lamda,因此您可以一次性执行"获取或添加"。它默认为 20 分钟滑动过期,但您可以设置您喜欢的任何缓存策略。
有关缓存任务的详细信息,请参阅 api 文档,你可能会发现用于演示缓存任务的示例 webapi 应用非常有用。
(免责声明:我是LazyCache的作者)
我建议你使用MemoryCache
MemoryCache cache = MemoryCache.Default;
string cacheName = "mycachename";
if cache.Contains(cacheName) == false || cache[cacheName] == null)
{
// load data
var data = await response.Content.ReadAsAsync<T>();
// save data to cache
cache.Set(cacheName, data, new CacheItemPolicy() { SlidingExpiration = DateTime.Now.AddDays(1).TimeOfDay });
}
return cache[cacheName];