What happens when Kotlin coroutines interact with blocking legacy libraries?

Blocking libraries block threads inside coroutine contexts, reducing scalability.

When coroutines call blocking APIs (like JDBC or legacy HTTP clients), they block underlying threads in the dispatcher. This breaks coroutine scalability assumptions because threads are a limited resource. Overuse leads to thread starvation, especially in Dispatchers.Default or IO. Proper handling requires wrapping blocking calls in withContext(Dispatchers.IO) or migrating to non-blocking alternatives.