static async Task DownLoad(GetContentsAsync GetContentsAsync)
{
await DownLoadInner(GetContentsAsync).ConfigureAwait(false);
await DownLoadInner(GetContentsAsync).ConfigureAwait(false);
//await Task.WhenAll(new Task[]{ DownLoadInner(GetContentsAsync), DownLoadInner(GetContentsAsync)});
//如果用了WhenAll，则两个会同时执行，而无法利用Cahche的结果。
}
static async Task DownLoadInner(GetContentsAsync GetContentsAsync)
{
string[] urls = new string[]
{
"http://msdn.microsoft.com",
"http://www.contoso.com",
"http://www.microsoft.com"
};
Stopwatch stopwatch = new Stopwatch();
stopwatch.Start();
var results = await Task.WhenAll(urls.Select(url => GetContentsAsync(url))).ConfigureAwait(false);
stopwatch.Stop();
Console.WriteLine("Retrieved {0} characters. Elapsed time was {1} ms.",
results.Sum(result => result.Length),
stopwatch.ElapsedMilliseconds);
}
public static Task <string> GetContentsAsync(string url)
{
Task <string> contents;
if (!s_urlToContents.TryGetValue(url, out contents))
{
Console.WriteLine("Before call @" + Thread.CurrentThread.ManagedThreadId);
GetContentsAsync GetContentsAsyncInner = async(u) => {
Console.WriteLine("async {@" + Thread.CurrentThread.ManagedThreadId);
var content = await new WebClient().DownloadStringTaskAsync(url);
//var content = await new WebClient().DownloadStringTaskAsync(url).ConfigureAwait(false);
Console.WriteLine("async }@" + Thread.CurrentThread.ManagedThreadId);
s_urlToContents.TryAdd(url, Task.FromResult(content));
return(content);
};
//这个版本试验直接在里面定义async lambda
contents = GetContentsAsyncInner(url);
}
return(contents);
}
