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As new to Kotlin, I am facing a little problem in understanding the difference between thread and coroutine. Can someone make it simple to understand the fundamental them of them?

I started learning core concepts of Kotlin programing language recently, but I got stuck in differentiating threads and coroutines.

Waseem Sajad
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Threads are native mechanisms, whereas coroutines are user-level abstractions, which use threads and actually make better use of them.

Key differences I can point out:

  • Thread is a different mechanism, which is linked to the native thread of OS. This is the reason why creating hundreds/thousands of threads is impossible - thread consumes a lot of OS' memory. Coroutine is a user-level abstraction of some worker which does not use excessive amount of memory, since it is not linked to native resources and use resources of JVM heap.

  • Thread gets blocked instead of suspending and dispatching the job to another thread.

  • Thread cannot be used until its work completes.

  • Coroutine is a user-friendly abstraction which allows you to reuse thread's resources to execute suspending functions. Mechanism is following: suspending function is called from a coroutine and dispatched on a specific thread. While it suspends, thread resources can be used to execute another suspending function.

To get better understanding of how coroutines work in combination with threads, you can read my answer to my own question, which is also a source for this answer.

Steyrix
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  • Last bullet point could be misleading. Starting a thread or launching a coroutine are both asynchronous. The code within a thread’s `run` or a coroutine’s lambda are both synchronous. You might be conflating the terms coroutine and suspend function. – Tenfour04 Feb 15 '23 at 12:45
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    @Tenfour04 yep, I misworded that one. Thank you for pointing out – Steyrix Feb 15 '23 at 13:07