ASP.NET SynchronizationContext Example

Blog Post

ASP.NET Classic & Core Web API (running full framework)

Referencing a .NET 4.7.2 async library

Api Call	Description	Deadlock Classic?	Deadlock Core?
api/values	normal call	❌	❌
api/values/framework/async	async/await	❌	❌
api/values/framework/sync?configAwait=false	synchronous blocking	❌	❌
api/values/framework/sync?configAwait=true	synchronous blocking	✔️	❌

Referencing a .NET Standard async library

Api Call	Description	Deadlock Classic?	Deadlock Core?
api/values	normal call	❌	❌
api/values/standard/async	async/await	❌	❌
api/values/standard/sync?configAwait=false	synchronous blocking	❌	❌
api/values/standard/sync?configAwait=true	synchronous blocking	✔️	❌

Simply, ConfigureAwait(false) is not required in an ASP.NET Core application (regardless of whether it's running with the full framework or core). This is because the SynchronizationContext is not determined by the runtime!