VSTHRD012 Provide JoinableTaskFactory where allowed

When constructing types or calling methods that accept a JoinableTaskFactory or JoinableTaskContext, take the opportunity to supply one if your application has a main thread with a single threaded SynchronizationContext such as WPF or WinForms.

Examples of patterns that are flagged by this analyzer

void F() {
    var o = new AsyncLazy<int>(() => Task.FromResult(1)); // analyzer flags this line
}

Solution

Call the overload that accepts a JoinableTaskFactory or JoinableTaskContext instance:

void F() {
    var o = new AsyncLazy<int>(() => Task.FromResult(1), this.JoinableTaskFactory);
}

Suppression

You can suppress the diagnostic by explicitly specifying null for the argument:

void F() {
    var o = new AsyncLazy<int>(() => Task.FromResult(1), null);
}