我一直试图在等待多个线程时合并几个问题的结果,但是我等待Task.WhenAll(Tasks);
的调用在所有任务完成之前已经通过!
List<Task> tasks = new List<Task>();
foreach (DownloadingFile file in downloadingFiles)
{
Task t = new Task(async delegate { await file.PollDownload(); } );
tasks.Add(t);
t.Start();
}
await Task.WhenAll(tasks);
internal async Task PollDownload()
{
string localFile = "pathToDestination";
WebRequest headerRequest = WebRequest.Create(uri);
headerRequest.Method = "HEAD";
HttpWebResponse response = null;
try
{
response = (HttpWebResponse) await headerRequest.GetResponseAsync();
}
catch
{
Thread.Sleep(500);
try
{
response = (HttpWebResponse)await headerRequest.GetResponseAsync();
}
catch
{
response = null;
}
}
if (response == null)
{
state = DOWNLOAD_STATE.FAILED;
return;
}
totalBytes = response.ContentLength;
state = DOWNLOAD_STATE.WAITING_START;
//Check to see whether a local copy of the remote file exists
if (File.Exists(localFile))
{
DateTime localFileUpdated = File.GetCreationTimeUtc(localFile);
DateTime onlineFileUpdated = response.LastModified;
// If the download date of the local file comes after the modification date of the remote copy
// then we do not need to take any further action here.
if (onlineFileUpdated <= localFileUpdated)
{
state = DOWNLOAD_STATE.SKIPPED;
}
//Otherwise we should remove the local copy and proceed with the download
else
{
File.Delete(localFile);
}
}
return;
}
我认为这是因为任务包含 async 委托方法?我不希望它们是异步的,但是它们必须是因为PollDownload()
等待其他异步方法(尽管在这里可以将它们更改为同步方法,但在此问题的其他情况下,它们不能更改为同步方法。所以我仍然需要一个解决方案。
答案 0 :(得分:4)
new Task()
接受Action
,因此您传递的async void
不会等待其结果。
您应该改用Task.Run(),它也接受Func<Task>
。