VSTHRD115 Avoid creating a JoinableTaskContext with an explicit null SynchronizationContext

Constructing a JoinableTaskContext with an explicit null SynchronizationContext is not recommended as a means to construct an instance for use in unit tests or processes without a main thread. This is because the constructor will automatically use SynchronizationContext.Current in lieu of a non-null argument. If SynchronizationContext.Current happens to be non-null, the constructor may unexpectedly configure the new instance as if a main thread were present.

Examples of patterns that are flagged by this analyzer

void SetupJTC() {
    this.jtc = new JoinableTaskContext(null, null);
}

This code appears to configure the JoinableTaskContext to not be associated with any SynchronizationContext. But in fact it will be associated with the current SynchronizationContext if one is present.

Solution

If you intended to inherit SynchronizationContext.Current to initialize with a main thread, provide that value explicitly as the second argument to suppress the warning:

void SetupJTC() {
    this.jtc = new JoinableTaskContext(null, SynchronizationContext.Current);
}

If you intended to create a JoinableTaskContext for use in a unit test or in a process without a main thread, call JoinableTaskContext.CreateNoOpContext() instead:

void SetupJTC() {
    this.jtc = JoinableTaskContext.CreateNoOpContext();
}

Code fixes are offered to update code to either of the above patterns.