Kotlinmedium

What does `suspend` mean in Kotlin coroutines (and what does it NOT mean)?

Answer

`suspend` means the function can pause without blocking the thread and resume later. It does NOT automatically mean “runs on a new thread” — the dispatcher decides where it runs.

suspend fun loadUser(id: String): User {
  // can suspend here (e.g., awaiting IO)
  return api.getUser(id)
}

Advanced answer

Deep dive

Expanding on the short answer — what usually matters in practice:

Context (tags): coroutines, suspend, dispatcher
JVM: memory (heap/stack), GC, and what drives latency.
Contracts: equals/hashCode/toString, mutability and consequences.
Performance: boxing, allocations, collections, inlining.
Explain the "why", not just the "what" (intuition + consequences).
Trade-offs: what you gain/lose (time, memory, complexity, risk).
Edge cases: empty inputs, large inputs, invalid inputs, concurrency.

Examples

Here’s an additional example (building on the short answer):

suspend fun loadUser(id: String): User {
  // can suspend here (e.g., awaiting IO)
  return api.getUser(id)
}

Common pitfalls

Too generic: no concrete trade-offs or examples.
Mixing average-case and worst-case (e.g., complexity).
Ignoring constraints: memory, concurrency, network/disk costs.

Interview follow-ups

When would you choose an alternative and why?
What production issues show up and how do you diagnose them?