Kotlin coroutine - behind the scenes
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Coroutines allow performing concurrent operations without threads by using continuation-passing style and suspension functions. Coroutines are lightweight and efficient compared to threads. Behind the scenes, coroutines use a state machine and continuation objects to pause and resume computation across suspension points, providing an appearance of concurrency through asynchronous operations.
Kotlin coroutine - behind the scenes
- 1. Kotlin Coroutine Behind of the scenes Anh Vu [email protected] @anhvt52
- 2. Concurrency is not parallelism
- 3. Concurrency is about dealing with lots of things at once
- 4. Concurrency is about dealing with lots of things at once Parallelism is about doing lots of things at once
- 5. Go to office Input info Go back Do SliceQueue
- 6. Queue Go to office Input info Go back Do Slice Do Slice
- 7. Go to office Input info Go back Do Slice Queue
- 11. Suspending function Thread Function B Function A Suspended
- 12. suspend fun backgroundTask(param: Int): Int { // long running operation }
- 13. suspend fun backgroundTask(param: Int): Int { // long running operation }
- 14. Continuation interface Continuation<in T> { val context: CoroutineContext fun resumeWith(result: Result<T>) } fun <T> Continuation<T>.resume(value: T) fun <T> Continuation<T>.resumeWithException(exception: Throwable)
- 15. suspend fun <T> CompletableFuture<T>.await(): T = suspendCoroutine<T> { cont: Continuation<T> -> whenComplete { result, exception -> if (exception == null) // the future has been completed n cont.resume(result) else // the future has completed with an exception cont.resumeWithException(exception) } } }
- 18. Thread Pool
- 20. Coroutines
- 21. coroutineScope { // Creates a coroutine scope launch { //coroutine builder withContext(Dispatchers.IO) { //context switching doABigTask() //execute task } } } suspend fun doABigTask() { //… }
- 26. Coroutines are light-weight fun main() = runBlocking { repeat(100_000) { // launch a lot of coroutines launch { delay(1000L) print(".") } } }
- 27. Job and Deferred
- 28. Job and Deferred fun CoroutineScope.launch( context: CoroutineContext = EmptyCoroutineContext, // ... ): Job
- 30. Coroutine Scope
- 31. Coroutine Scope fun CoroutineScope.launch( context: CoroutineContext = EmptyCoroutineContext, // ... ): Job
- 32. class MyActivity : AppCompatActivity(), CoroutineScope by MainScope() { override fun onDestroy() { cancel() // cancel is extension on CoroutineScope } //... }
- 33. public fun MainScope(): CoroutineScope = ContextScope(SupervisorJob() + Dispatchers.Main)
- 35. launch { // context of the parent, main runBlocking coroutine println("main runBlocking: ${Thread.currentThread().name}") } launch(Dispatchers.Unconfined) { // not confined -- will work with main thread println("Unconfined: ${Thread.currentThread().name}") } launch(Dispatchers.Default) { // will get dispatched to DefaultDispatcher println("Default: ${Thread.currentThread().name}") } launch(newSingleThreadContext("MyOwnThread")) { // will get its own new thread println("newSingleThreadContext: ${Thread.currentThread().name}") } //sampleEnd
- 38. Continuation passing style suspend fun <T> CompletableFuture<T>.await(): T fun <T> CompletableFuture<T>.await(continuation: Continuation<T>): Any?
- 39. suspend fun postItem(item: Item) { val token = requestToken() val post = createPost(token, item) processPost(post) } suspend fun requestToken() { //.. } supsend fun createPost(token: String, item: Item) { //.. }
- 40. fun postItem(item: Item) { requestToken { token -> createPost(token, item) { post -> processPost(post) } } } suspend fun postItem(item: Item) { val token = requestToken() val post = createPost(token, item) processPost(post) } Callbacks
- 41. State machine
- 42. Labelling suspend fun postItem(item: Item) { // LABEL 0 val token = requestToken() // LABEL 1 val post = createPost(token, item) // LABEL 2 processPost(post) }
- 43. Labelling suspend fun postItem(item: Item) { switch (label) { case 0: val token = requestToken() case 1: val post = createPost(token, item) case 2: processPost(post) } }
- 44. State suspend fun postItem(item: Item) { val sm = object : CoroutineImpl { … } switch (label) { case 0: val token = requestToken() case 1: val post = createPost(token, item) case 2: processPost(post) } }
- 45. CPS transform fun postItem(item: Item, cont: Continuation) { val sm = object : CoroutineImpl { … } switch (label) { case 0: val token = requestToken(sm) case 1: val post = createPost(token, item, sm) case 2: processPost(post) } }
- 46. Store state fun postItem(item: Item,cont: Continuation) { val sm = object : CoroutineImpl { … } switch (label) { case 0: sm.item = item sm.label = 1 val token = requestToken(sm) case 1: //... } }
- 47. Store state fun postItem(item: Item, cont: Continuation) { val sm = object : CoroutineImpl { fun resume(…) { postItem(null, this) } } switch (label) { case 0: sm.item = item sm.label = 1 val token = requestToken(sm) case 1: //... } }
- 48. Restore state fun postItem(item: Item,cont: Continuation) { val sm = .. switch (label) { case 0: //... case 1: val item = sm.item val token = sm.result as Token sm.label = 2 createPost(token, item, sm) //... } }
- 49. State machine vs Callbacks
- 50. fun postItem(item: Item) { requestToken { token -> createPost(token, item) { post -> processPost(post) } } } suspend fun postItem(item: Item) { val token = requestToken() val post = createPost(token, item) processPost(post) } Callbacks
- 51. Q&A