A deep dive into the Finite-State-Machine (FSM) transformation that powers Kotlin Coroutines, from Compiler Mechanics to Structured Concurrency

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Kotlin coroutines use compiler-generated finite state machines (FSMs) to enable suspendable functions on the JVM. The compiler transforms suspend functions by adding a hidden Continuation parameter, converting local variables into state machine fields, and generating switch-based state transitions. Each suspension point creates a new state, with the label field tracking execution position. When a suspend function pauses, it returns COROUTINE_SUSPENDED and stores state in heap memory; resumption continues from the exact point via continuation.resumeWith(). Dispatchers handle transparent thread switching by intercepting continuations. The article covers state preservation, continuation chaining, exception propagation, and practical patterns like converting callbacks to suspend functions using suspendCoroutine.

Inside Kotlin Coroutines: State Machines, Continuations, and Structured Concurrency.