How are coroutines implemented and work inside the system at a low level?

Coroutines in Android (for example, in Kotlin) are implemented as lightweight threads managed at the library level rather than by the OS. At a low level, a coroutine is an object that contains the execution state (stack, local variables, and suspension point).

Key points of coroutine operation:

• Coroutines use a continuation mechanism that saves the function's state at the point of suspension.
• When a suspend function is called, the coroutine can suspend, saving its context, and resume later without blocking the thread.
• The coroutine dispatcher decides on which thread or thread pool to execute the coroutine.
• Unlike OS threads, coroutines are very lightweight, allowing the creation of thousands of coroutines without significant resource costs.

Thus, coroutines implement asynchronous and concurrent programming by saving and restoring function states, managed by the library rather than system threads.