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https://github.com/badoo/Reaktive

Kotlin multi-platform implementation of Reactive Extensions
https://github.com/badoo/Reaktive

android cross-platform hacktoberfest ios kotlin kotlin-multiplatform kotlin-native multi-platform multiplatform reactive reaktive rx rxkotlin

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Kotlin multi-platform implementation of Reactive Extensions

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[![Maven Central](https://img.shields.io/maven-central/v/com.badoo.reaktive/reaktive?color=blue)](https://search.maven.org/artifact/com.badoo.reaktive/reaktive)

[![Build Status](https://github.com/badoo/Reaktive/workflows/Build/badge.svg?branch=master)](https://github.com/badoo/Reaktive/actions)

[![License](https://img.shields.io/badge/License-Apache/2.0-blue.svg)](https://github.com/badoo/Reaktive/blob/master/LICENSE)

[![kotlinlang|reaktive](https://img.shields.io/badge/kotlinlang-reaktive-blue?logo=slack)](https://kotlinlang.slack.com/archives/CU05HB31A)



Kotlin multiplatform implementation of Reactive Extensions.



Should you have any questions or feedback welcome to the **Kotlin Slack channel**: 

[#reaktive](https://kotlinlang.slack.com/archives/CU05HB31A)



## Setup



There are a number of modules published to Maven Central:



- `reaktive` - the main Reaktive library (multiplatform)

- `reaktive-annotations` - collection of annotations (mutiplatform)

- `reaktive-testing` - testing utilities (multiplatform)

- `utils` - some utilities like `Clock`, `AtomicReference`, `Lock`, etc. (multiplatform)

- `coroutines-interop` - Kotlin coroutines interoperability helpers (multiplatform)

- `rxjava2-interop` - RxJava v2 interoperability helpers (JVM and Android)

- `rxjava3-interop` - RxJava v3 interoperability helpers (JVM and Android)



### Configuring dependencies



```groovy

kotlin {

    sourceSets {

        commonMain {

            dependencies {

                implementation 'com.badoo.reaktive:reaktive:'

                implementation 'com.badoo.reaktive:reaktive-annotations:'

                implementation 'com.badoo.reaktive:coroutines-interop:' // For interop with coroutines

                implementation 'com.badoo.reaktive:rxjava2-interop:' // For interop with RxJava v2

                implementation 'com.badoo.reaktive:rxjava3-interop:' // For interop with RxJava v3

            }

        }



        commonTest {

            dependencies {

                implementation 'com.badoo.reaktive:reaktive-testing:'

            }

        }

    }

}

```



## Features:



* Multiplatform: JVM, Android, iOS, macOS, watchOS, tvOS, JavaScript, Linux X64

* Schedulers support: 

  * `computationScheduler` - fixed thread pool equal to a number of cores

  * `ioScheduler` - unbound thread pool with caching policy

  * `newThreadScheduler` - creates a new thread for each unit of work

  * `singleScheduler` - executes tasks on a single shared background thread

  * `trampolineScheduler` - queues tasks and executes them on one of the participating threads

  * `mainScheduler` - executes tasks on main thread

* True multithreading for Kotlin/Native (since v2.0 only the [new memory model](https://kotlinlang.org/docs/native-memory-manager.html) is supported)

* Supported sources: `Observable`, `Maybe`, `Single`, `Completable`

* Subjects: `PublishSubject`, `BehaviorSubject`, `ReplaySubject`, `UnicastSubject`

* Interoperability with Kotlin Coroutines

  * Convert `suspend` functions to/from `Single`, `Maybe` and `Completable`

  * Convert `Flow` to/from `Observable`

  * Convert `CoroutineContext` to `Scheduler`

  * Convert `Scheduler` to `CoroutineDispatcher`

* Interoperability with RxJava2 and RxJava3

  * Conversion of sources and schedulers between Reaktive and RxJava



## Reaktive and Kotlin/Native 



Since version 2.x, Reaktive only works with the [new memory model](https://kotlinlang.org/docs/native-memory-manager.html).



    Reaktive 1.x and the old (strict) memory model



The old (strict) Kotlin Native memory model and concurrency are very special. In general shared mutable state between threads is not allowed.

Since Reaktive supports multithreading in Kotlin Native, please read the following documents before using it:



* [Concurrency](https://kotlinlang.org/docs/reference/native/concurrency.html#object-transfer-and-freezing)

* [Immutability](https://kotlinlang.org/docs/reference/native/immutability.html)



Object detachment is relatively difficult to achieve and is very error-prone when the objects are created from outside and

are not fully managed by the library. This is why Reaktive prefers frozen state. Here are some hints:



* Any callback (and any captured objects) submitted to a Scheduler will be frozen

* `subscribeOn` freezes both its upstream source and downstream observer,

all the Disposables (upstream's and downstream's) are frozen as well,

all the values (including errors) are **not** frozen by the operator

* `observeOn` freezes only its downstream observer and all the values (including errors) passed through it, plus all the Disposables,

upstream source is **not** frozen by the operator

* Other operators that use scheduler (like `debounce`, `timer`, `delay`, etc.) behave same as `observeOn` in most of the cases



#### Thread local tricks to avoid freezing



Sometimes freezing is not acceptable, e.g. we might want to load some data in background and then update the UI.

Obviously UI can not be frozen. With Reaktive it is possible to achieve such a behaviour in two ways:



Use `threadLocal` operator:



```kotlin

val values = mutableListOf()

var isFinished = false



observable { emitter ->

    // Background job

}

    .subscribeOn(ioScheduler)

    .observeOn(mainScheduler)

    .threadLocal()

    .doOnBeforeNext { values += it } // Callback is not frozen, we can update the mutable list

    .doOnBeforeFinally { isFinished = true } // Callback is not frozen, we can change the flag

    .subscribe()

```



Set `isThreadLocal` flag to `true` in `subscribe` operator:



```kotlin

val values = mutableListOf()

var isComplete = false



observable { emitter ->

    // Background job

}

    .subscribeOn(ioScheduler)

    .observeOn(mainScheduler)

    .subscribe(

        isThreadLocal = true,

        onNext = { values += it }, // Callback is not frozen, we can update the mutable list

        onComplete = { isComplete = true } // Callback is not frozen, we can change the flag

    )

```



In both cases subscription (`subscribe` call) **must** be performed on the Main thread.



## Coroutines interop



This functionality is provided by the `coroutines-interop` module. Please mind some [known problems](https://github.com/Kotlin/kotlinx.coroutines/blob/native-mt/kotlin-native-sharing.md#known-problems) with multi-threaded coroutines on Kotlin/Native.



### Examples



```kotlin

val flow: Flow = observableOf(1, 2, 3).asFlow()

val observable: Observable = flowOf(1, 2, 3).asObservable()

```



```kotlin

fun doSomething() {

    singleFromCoroutine { getSomething() }

        .subscribe { println(it) }

}



suspend fun getSomething(): String {

    delay(1.seconds)

    return "something"

}

```



```kotlin

val defaultScheduler = Dispatchers.Default.asScheduler()

val computationDispatcher = computationScheduler.asCoroutineDispatcher()

```



## Subscription management with DisposableScope



Reaktive provides an easy way to manage subscriptions: [DisposableScope](https://github.com/badoo/Reaktive/blob/master/reaktive/src/commonMain/kotlin/com/badoo/reaktive/disposable/scope/DisposableScope.kt).



Take a look at the following examples:



```kotlin

val scope =

    disposableScope {

        observable.subscribeScoped(...) // Subscription will be disposed when the scope is disposed



        doOnDispose {

            // Will be called when the scope is disposed

        }



        someDisposable.scope() // `someDisposable` will be disposed when the scope is disposed

    }



// At some point later

scope.dispose()

```



```kotlin

class MyPresenter(

    private val view: MyView,

    private val longRunningAction: Completable

) : DisposableScope by DisposableScope() {



    init {

        doOnDispose {

            // Will be called when the presenter is disposed

        }

    }



    fun load() {

        view.showProgressBar()



        // Subscription will be disposed when the presenter is disposed

        longRunningAction.subscribeScoped(onComplete = view::hideProgressBar)

    }

}



class MyActivity : AppCompatActivity(), DisposableScope by DisposableScope() {

    override fun onCreate(savedInstanceState: Bundle?) {

        super.onCreate(savedInstanceState)



        MyPresenter(...).scope()

    }



    override fun onDestroy() {

        dispose()



        super.onDestroy()

    }

}

```



## Reaktive and Swift interoperability



Please see the corresponding documentation page: [Reaktive and Swift interoperability](docs/SwiftInterop.md).



## Plugins



Reaktive provides Plugin API, something similar to [RxJava plugins](https://github.com/ReactiveX/RxJava/wiki/Plugins). The Plugin API provides a way to decorate Reaktive sources. A plugin should implement the [ReaktivePlugin](https://github.com/badoo/Reaktive/blob/master/reaktive/src/commonMain/kotlin/com/badoo/reaktive/plugin/ReaktivePlugin.kt) interface, and can be registered using the `registerReaktivePlugin` function and unregistered using the `unregisterReaktivePlugin` function.



```kotlin

object MyPlugin : ReaktivePlugin {

    override fun  onAssembleObservable(observable: Observable): Observable =

        object : Observable {

            private val traceException = TraceException()



            override fun subscribe(observer: ObservableObserver) {

                observable.subscribe(

                    object : ObservableObserver by observer {

                        override fun onError(error: Throwable) {

                            observer.onError(error, traceException)

                        }

                    }

                )

            }

        }



    override fun  onAssembleSingle(single: Single): Single =

        TODO("Similar to onAssembleSingle")



    override fun  onAssembleMaybe(maybe: Maybe): Maybe = 

        TODO("Similar to onAssembleSingle")



    override fun onAssembleCompletable(completable: Completable): Completable =

        TODO("Similar to onAssembleSingle")



    private fun ErrorCallback.onError(error: Throwable, traceException: TraceException) {

        if (error.suppressedExceptions.lastOrNull() !is TraceException) {

            error.addSuppressed(traceException)

        }

        onError(error)

    }



    private class TraceException : Exception()

}

```



## Samples:



* [MPP module](https://github.com/badoo/Reaktive/tree/master/sample-mpp-module)

* [Android app](https://github.com/badoo/Reaktive/tree/master/sample-android-app)

* [iOS app](https://github.com/badoo/Reaktive/tree/master/sample-ios-app)

* [JavaScript browser app](https://github.com/badoo/Reaktive/tree/master/sample-js-browser-app)

* [Linux x64 app](https://github.com/badoo/Reaktive/tree/master/sample-linuxx64-app)