Task.Run not running in background but on Dispatcher

Question

I have one of my CPU intensive tasks blocking the UI thread, after investigating I've found that the root of the problem seems to be the Task.Run actually running in the Dispatcher thread:

Task.Run(() =>
{
    if (Dispatcher.CurrentDispatcher.Thread == Thread.CurrentThread)
    {
        // breakpoint
    }
});

Placing a breakpoints in the if statement is hit.

Is this expected behaviour? I understood Task.Run to use a different thread.

mm8 · Accepted Answer · 2018-09-07T15:05:33.770

2

The action that you pass to Task.Run is executed on a thread pool thread if you use the default task scheduler (which you are by default).

This should give you the expected result:

Task.Run(() =>
{
    if (System.Windows.Application.Current.Dispatcher.Thread == Thread.CurrentThread)
    {
        // breakpoint not hit in WPF...
    }
});

There is a difference between System.Windows.Application.Current.Dispatcher and System.Windows.Threading.Dispatcher.CurrentDispatcher:

Dispatcher.CurrentDispatcher vs. Application.Current.Dispatcher

edited Sep 07 '18 at 15:05

answered Sep 07 '18 at 14:55

mm8

163,881
10
57
88

I knew I must have been doing something stupid. Thanks. – Joe Sep 07 '18 at 15:51
It is easy to accidentally type Dispatcher.CurrentDispatcher by mistake with auto complete. – rollsch Sep 05 '21 at 06:01

Task.Run not running in background but on Dispatcher

1 Answers1