How do I refactor legacy synchronous code to avoid deadlocks?

Legacy Code Pitfalls

Older .NET codebases often rely on blocking patterns: Task.Wait(), .Result, and Task.Factory.StartNew with synchronous continuations. Migrating these to pure async/await without understanding the synchronization context is a fast track to production outages.

Refactoring Steps

• Replace .Result and .Wait() with await everywhere possible.
• Audit all entry points—web controllers, background services, and message handlers—for blocking calls.
• Introduce ConfigureAwait(false) in library layers to break context capture.
• Add unit tests that simulate high concurrency to surface hidden blocking behavior.

Start with the call graph. If a method is called from both sync and async paths, you may need to split it or introduce an async wrapper. Do not simply sprinkle async keywords on existing methods; that often leaves the blocking calls intact.