.net core api使用Memory Cache

在ASP.NET CORE中使用内存缓存还是比较容易的，现在主程序中配置内存缓存

builder.Services.AddMemoryCache( o => {
    o.SizeLimit = 100;
});

在控制器中注入MemoryCache服务

private readonly IMemoryCache _memoryCache;

public CacheRequestController(IMemoryCache memoryCache)
{
    _memoryCache = memoryCache;
}

在控制器中实现一个接受路径参数的方法，通过生成多次uuid以实现一个耗时操作。

[HttpGet("{id}")]
public IActionResult Get(string id)
{
    _logger.LogInformation("Request id: {0}", id);
    var beforeTime = DateTime.Now;
    string? result = _memoryCache.GetOrCreate(id, entry => {
        string? uuid = null;
        for (int i = 0; i < 2048; ++i) {
            uuid = Guid.NewGuid().ToString("N");
        }
        return uuid;
    });
    var endTime = DateTime.Now;
    var delta = endTime - beforeTime;

    return Ok(new { Id = id, Result = result, Time = delta.Microseconds.ToString() });
}

一顿操作猛如虎之后，发生了以下错误

An exception of type 'System.InvalidOperationException' occurred in Microsoft.Extensions.Caching.Memory.dll but was not handled in user code: 'Cache entry must specify a value for Size when SizeLimit is set.'

解决报错的问题：

https://github.com/stefanprodan/AspNetCoreRateLimit/issues/148

根据图中答案进行修改，得到正确运行的代码。

[HttpGet("{id}")]
public IActionResult Get(string id)
{
    _logger.LogInformation("Request id: {0}", id);
    var beforeTime = DateTime.Now;
    string? result = _memoryCache.GetOrCreate(id, entry => {
        string? uuid = null;
        entry.Priority = CacheItemPriority.High;
        entry.Size = 1;
        for (int i = 0; i < 2048; ++i) {
            uuid = Guid.NewGuid().ToString("N");
        }
        return uuid;
    });
    var endTime = DateTime.Now;
    var delta = endTime - beforeTime;

    return Ok(new { Id = id, Result = result, Time = delta.Microseconds.ToString() });
}

通过结果我们可以看到没有缓存的运行实践大概是在400毫秒，而获取缓存值大概是在30毫秒内。

{
  "id": "uid",
  "result": "8cb3e67bc55e40f3bf9c1b3a097bd7f8",
  "time": "408"
}

获取已有缓存的请求结果

{
  "id": "uid",
  "result": "8cb3e67bc55e40f3bf9c1b3a097bd7f8",
  "time": "17"
}