c# - 限制重复请求

Question

我正在寻找一种方法来限制 HttpModule 中的重复请求。不幸的是，我不断收到以下错误:我正在寻找一个有解释的解决方案。

System.ObjectDisposedException: The semaphore has been disposed.

System.ObjectDisposedException: The semaphore has been disposed. at System.Threading.SemaphoreSlim.CheckDispose() at System.Threading.SemaphoreSlim.Release(Int32 releaseCount) at System.Threading.SemaphoreSlim.Release()

我的做法如下。

// Container for semaphores
private static readonly ConcurrentDictionary<string, SemaphoreSlim> 
SemaphoreSlims = new ConcurrentDictionary<string, SemaphoreSlim>();

// Wrapper for getting semaphore
private static SemaphoreSlim GetSemaphoreSlim(string id)
{
    return SemaphoreSlims.GetOrAdd(id, new SemaphoreSlim(1, 1));
}


private async Task ProcessImageAsync(HttpContext context)
{
    // `hash` is the request path hashed.
    SemaphoreSlim semaphore = GetSemaphoreSlim(hash);
    await semaphore.WaitAsync();

    try
    {

    // Do awaitable task

    }
    finally
    {
        semaphore.Release();
    }
}

Dispose() 仅在处理 httpModule 本身期间(由我)调用。

private void Dispose(bool disposing)
{
    if (this.isDisposed)
    {
        return;
    }

    if (disposing)
    {
        // Dispose of any managed resources here.
        foreach (KeyValuePair<string, SemaphoreSlim> semaphore in SemaphoreSlims)
        {
            semaphore.Value.Dispose();
        }

        SemaphoreSlims.Clear();
    }

    // Call the appropriate methods to clean up
    // unmanaged resources here.
    // Note disposing is done.
    this.isDisposed = true;
}

Answer 1

Apparently, both HttpApplication and HttpModule's are instantiated multiple times. (这种设计在我看来非常有问题。换句话说，这是 ASP.NET 中的一个设计缺陷。这些实例应该像每个人所期望的那样是单例。)

静态字典正在被释放的多个实例处理。

您根本不需要处置。只需让操作系统在工作进程死亡时删除这些资源即可。

不是，你的字典会无限增长。

此外，您传递给 GetOrAdd 的信号量实例几乎总是会在未被处置的情况下泄漏。