Reputation: 2013
I have been trying to combine the results of several questions on waiting for multiple threads, but my call to await Task.WhenAll(Tasks);
is being passed before all tasks are finished!
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;
}
I assume this is because the Tasks include async delegate methods? I don't WANT them to be async but they need to be because of the PollDownload()
awaits other async methods ( though they can probably be changed to synchronous methods here they cannot be changed to synchronous methods in another instance of this problem so I still need a solution).
Upvotes: 0
Views: 307
Reputation: 888303
new Task()
accepts an Action
, so you're passing an async void
that does not wait for its result.
You should use Task.Run() instead, which also accepts Func<Task>
.
Upvotes: 4