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Programação Assíncrona com Kotlin Coroutines Wellington Costa Pereira

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Wellington Costa Pereira ● +4 anos de experiência ● Mestrando em Ciências da Computação ● Android Leader na Resource IT Solutions ● Open source <3 ● Compartilhar conhecimento <3 GitHub: https://github.com/WellingtonCosta E-mail: [email protected]

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Exemplo fun updateUserData(username: String) { val user = fetchUserFromApi(username) val repos = fetchReposFromApi(username) saveUserDataInDb(user, repos) }

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Estilo Tradicional fun updateUserData(username: String) { val user = fetchUserFromApi(username) val repos = fetchReposFromApi(username) saveUserDataInDb(user, repos) }

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Estilo Tradicional fun updateUserData(username: String) { val user = fetchUserFromApi(username) val repos = fetchReposFromApi(username) saveUserDataInDb(user, repos) }

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Estilo Tradicional fun updateUserData(username: String) { val user = fetchUserFromApi(username) val repos = fetchReposFromApi(username) saveUserDataInDb(user, repos) }

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Callbacks to the rescue

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Callback fun updateUserData(username: String) { fetchUserFromApi(username) { user -> fetchReposFromApi(username) { repos -> saveUserDataInDb(user, repos) } } }

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Callback fun updateUserData(username: String) { fetchUserFromApi(username) { user -> fetchReposFromApi(username) { repos -> saveUserDataInDb(user, repos) } } }

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Coroutines to the rescue

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Coroutines suspend fun updateUserData(username: String) { val user = fetchUserFromApi(username) val repos = fetchReposFromApi(username) saveUserDataInDb(user, repos) }

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Coroutines suspend fun updateUserData(username: String) { val user = fetchUserFromApi(username) val repos = fetchReposFromApi(username) saveUserDataInDb(user, repos) }

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Principais Conceitos

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Principais Conceitos ● Modificador suspend ● launch vs async ● Dispatchers ● withContext ● coroutineScope ● runBlocking

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Modificador suspend A suspending function is simply a function that can be paused and resumed at a later time. They can execute a long running operation and wait for it to complete without blocking.

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Modificador suspend suspend fun updateUserData(username: String) { val user = fetchUserFromApi(username) val repos = fetchReposFromApi(username) saveUserDataInDb(user, repos) }

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launch vs async launch: A background job. Conceptually, a job is a cancellable thing with a life-cycle that culminates in its completion. It returns a Job instance. async: Deferred value is a non-blocking cancellable future. It’s a Job that has a result. It returns a Deferred instance.

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launch vs async fun doSomething() { launch { // do some operation } }

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launch vs async private val jobs = ArrayList() fun doSomething() { jobs.add( launch { // do some operation } ) } override fun onCleared() { jobs.forEach { if(!it.isCancelled) it.cancel() } }

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launch vs async fun doSomething() { async { // do some operation } }

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launch vs async fun doSomething() { val deferred = async { // do some operation } val result = deferred.await() }

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launch vs async fun doSomething() { val result = async { // do some operation }.await() }

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Dispatchers ● Dispatchers.Main: A coroutine dispatcher that is confined to the Main thread operating with UI objects. ● Dispatchers.Default: A coroutine dispatcher to execute CPU-bound tasks. ● Dispatchers.IO: A coroutine dispatcher that is designed for offloading blocking IO tasks to a shared pool of threads.

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withContext Calls the suspending block with a given coroutine context, suspends until it completes and then returns the result.

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withContext suspend fun updateUserData(username: String) { withContext(Dispatchers.IO) { val user = fetchUserFromApi(username) val repos = fetchReposFromApi(username) saveUserDataInDb(user, repos) } }

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withContext suspend fun updateUserData(username: String) { withContext(Dispatchers.IO) { val user = fetchUserFromApi(username) val repos = fetchReposFromApi(username) saveUserDataInDb(user, repos) } }

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withContext suspend fun updateUserData(username: String) { withContext(Dispatchers.IO) { val user = fetchUserFromApi(username) val repos = fetchReposFromApi(username) saveUserDataInDb(user, repos) } }

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coroutineScope This function is designed for a parallel decomposition of work. When any child coroutine in this scope fails, this scope fails and all the rest of the children are cancelled.

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coroutineScope suspend fun processPayments(): List { coroutineScope { val payments = withContext(Dispatchers.IO) { async { loadPayments() } } val processedPayments = withContext(Dispatchers.Default) { async { calculateInterestRate(payments.await()) } } return processedPayments.await() } }

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runBlocking Runs new coroutine and blocks current thread until its completion.

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runBlocking suspend fun processPayments(): List { // load payments and calculate its interest rate } @Test fun myAwesomeTest() { val payments = processPayments() // assert payments interest rate }

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runBlocking suspend fun processPayments(): List { // load payments and calculate its interest rate } @Test fun myAwesomeTest() = runBlocking { val payments = processPayments() // assert payments interest rate }

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Perguntas?

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Obrigado!