节气门WebRequests
我想执行一堆WebRequest，但是设置了可以同时启动的数量的阈值.
I want to execute a bunch of WebRequests, but set a threshold on how many can be started simultaneously.
I came across this LimitedConcurrencyTaskScheduler example and tried to utilize it like so
scheduler = new LimitedConcurrencyLevelTaskScheduler(1);
taskFactory = new TaskFactory(scheduler);
...
private Task<WebResponse> GetThrottledWebResponse(WebRequest request)
{
return taskFactory.FromAsync<WebResponse>(request.BeginGetResponse, request.EndGetResponse, null);
}
但是，我注意到即使最大并发数为1，我的任务似乎仍以非FIFO顺序完成.当我在LimitedConcurrencyLevelTaskScheduler中放置断点时，很明显根本没有使用断点.我想我使用TaskFactory.FromAsync的方式并没有达到我的预期.
However I noticed that even with a max concurrency of 1, my tasks seemed to be completing in a non-FIFO order. When I put breakpoints in LimitedConcurrencyLevelTaskScheduler, it became apparent that it's not being used at all. I guess the way I'm using TaskFactory.FromAsync is not doing what I had expected.
是否有适当的方法来限制同时发出的WebRequest?
Is there a proper way to throttle simultaneous WebRequests?
当我在LimitedConcurrencyLevelTaskScheduler中放置断点时，很明显根本没有使用断点
When I put breakpoints in LimitedConcurrencyLevelTaskScheduler, it became apparent that it's not being used at all
那是正确的. FromAsync根本不使用TaskFactory.实际上，我不太了解为什么这种方法不是静态的.
That is correct. FromAsync doesn't use the TaskFactory at all. In fact, I don't really understand why this method isn't static.
您可以通过多种方式来实现节流.您可以使用Microsoft.Tpl.Dataflow中的ActionBlock.或者，您也可以使用SemaphoreSlim:
You have multiple ways to implement the throttling. You could use the ActionBlock From Microsoft.Tpl.Dataflow. Or you could make your own using SemaphoreSlim:
private static readonly SemaphoreSlim Semaphore = new SemaphoreSlim(1);
private static async Task<WebResponse> GetThrottledWebResponse(WebRequest request)
{
await Semaphore.WaitAsync().ConfigureAwait(false);
try
{
return await request.GetResponseAsync().ConfigureAwait(false);
}
finally
{
Semaphore.Release();
}
}