IDLE - EndCheckForUpdates hangs

Question

I'm trying to use the IMAP IDLE feature to detect new mail. When a new mail is detected, the IDLE should stop and I will download the new mail.

However, when I call EndCheckForUpdates from the Notification event handler, it's just hanging. See example code below:

The class have these members:

Imap client; IAsyncResult async = null;

The client is properly connected to the server, and the inbox is selected. Then I do:

client.Notification += new ImapNotificationEventHandler(client_Notification); async = client.BeginCheckForUpdates(15*60000, CallBack, null);

This method is being called when a new mail arrives:

void client_Notification(object sender, ImapNotificationEventArgs e) { client.Abort(); // Tried both with and without this one if (async != null) client.EndCheckForUpdates(async); }

The problem is that the EndCheckForUpdates method call doesn't finish. How do I solve this? I want to cancel the IDLE as soon as I get a mail notification.

Accepted Answer

Please note the Notification event is blocking. It means the calling thread continues when the client_Notification method returns.

In your case you made a deadlock. EndCheckForUpdates cannot finish, because it is waiting for the Notification event to be finished which is waiting for the EndCheckForUpdates to be finished.

The correct usage is as follows:

client.Notification += new ImapNotificationEventHandler(client_Notification);
client.BeginCheckForUpdates(15*60000, CheckForUpdatesCallback, null);

void client_Notification(object sender, ImapNotificationEventArgs e)
{
    // abort IDLE state
    client.Abort();
}

void CheckForUpdatesCallback(IAsyncResult ar)
{
    // end the IDLE operation
    client.EndCheckForUpdates(ar);
}

IDLE - EndCheckForUpdates hangs

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