从异步请求返回缓存条目时锁定

Question

我编写了一个从 Web 服务获取一些信息的方法。 我想避免对服务的额外调用，所以我试图将信息放入 MemoryCache according to this post。

不同之处在于我在客户端没有“SomeHeavyAndExpensiveCalculation”，但我将工作委托给 Web 服务。所以我想等电话。

据我了解，对于当前的实现，我可以向 Web 服务器发出多个请求，因为我无法在锁内等待请求，这就是它被移出锁的原因。

有没有更好的解决方案？

谢谢。

 private static readonly object CompanyInfoLock = new object(); 

 public async Task<CompanyDto> GetCompanyInfo()
                {
                    const string cacheKey = "_COMPANYINFO_";

                    CompanyDto companyInfo = MemoryCache.Default[cacheKey] as CompanyDto;
                    if (companyInfo != null) return companyInfo;

                    CompanyDto company = await _userManagementService.InvokeAsync(x => x.GetCompanyAsync(AppPrincipal.Current.CurrentCompanyId));

                    lock (CompanyInfoLock)
                    {
                        companyInfo = MemoryCache.Default[cacheKey] as CompanyDto;
                        if (companyInfo != null) return companyInfo;
                        MemoryCache.Default.Add(cacheKey, company, new CacheItemPolicy
                        {
                            SlidingExpiration = new TimeSpan(2, 0, 0)
                        });
                    }

                    return company;
                }

Answer 1

使用SemaphoreSlim，以便您可以异步锁定并在调用 Web 服务之前放置锁定块。

private static readonly SemaphoreSlim CompanyInfoLock = new SemaphoreSlim (1); 

public async Task<CompanyDto> GetCompanyInfo()
{
    const string cacheKey = "_COMPANYINFO_";
    CompanyDto companyInfo;

    companyInfo = MemoryCache.Default[cacheKey] as CompanyDto;
    if (companyInfo != null) return companyInfo;

    await CompanyInfoLock.WaitAsync();
    try
    {
        //Check a 2nd time inside the lock to see if the cache has the data.
        companyInfo = MemoryCache.Default[cacheKey] as CompanyDto;
        if (companyInfo != null) return companyInfo;

        companyInfo = await _userManagementService.InvokeAsync(x => x.GetCompanyAsync(AppPrincipal.Current.CurrentCompanyId));

        MemoryCache.Default.Add(cacheKey, companyInfo, new CacheItemPolicy
        {
            SlidingExpiration = new TimeSpan(2, 0, 0)
        });

        return companyInfo;
    }
    finally
    {
        CompanyInfoLock.Release();
    }
}