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Maven Central Build Status License kotlinlang|reaktive

Kotlin multiplatform implementation of Reactive Extensions.

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

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

kotlin {
    sourceSets {
        commonMain {
            dependencies {
                implementation 'com.badoo.reaktive:reaktive:<version>'
                implementation 'com.badoo.reaktive:reaktive-annotations:<version>'
                implementation 'com.badoo.reaktive:coroutines-interop:<version>' // For interop with coroutines
                implementation 'com.badoo.reaktive:rxjava2-interop:<version>' // For interop with RxJava v2
                implementation 'com.badoo.reaktive:rxjava3-interop:<version>' // For interop with RxJava v3
            }
        }

        commonTest {
            dependencies {
                implementation 'com.badoo.reaktive:reaktive-testing:<version>'
            }
        }
    }
}

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 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.

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:

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:

val values = mutableListOf<Any>()
var isFinished = false

observable<Any> { 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:

val values = mutableListOf<Any>()
var isComplete = false

observable<Any> { 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 with multi-threaded coroutines on Kotlin/Native.

Examples

val flow: Flow<Int> = observableOf(1, 2, 3).asFlow()
val observable: Observable<Int> = flowOf(1, 2, 3).asObservable()
fun doSomething() {
    singleFromCoroutine { getSomething() }
        .subscribe { println(it) }
}

suspend fun getSomething(): String {
    delay(1.seconds)
    return "something"
}
val defaultScheduler = Dispatchers.Default.asScheduler()
val computationDispatcher = computationScheduler.asCoroutineDispatcher()

Subscription management with DisposableScope

Reaktive provides an easy way to manage subscriptions: DisposableScope.

Take a look at the following examples:

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()
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.

Plugins

Reaktive provides Plugin API, something similar to RxJava plugins. The Plugin API provides a way to decorate Reaktive sources. A plugin should implement the ReaktivePlugin interface, and can be registered using the registerReaktivePlugin function and unregistered using the unregisterReaktivePlugin function.

object MyPlugin : ReaktivePlugin {
    override fun <T> onAssembleObservable(observable: Observable<T>): Observable<T> =
        object : Observable<T> {
            private val traceException = TraceException()

            override fun subscribe(observer: ObservableObserver<T>) {
                observable.subscribe(
                    object : ObservableObserver<T> by observer {
                        override fun onError(error: Throwable) {
                            observer.onError(error, traceException)
                        }
                    }
                )
            }
        }

    override fun <T> onAssembleSingle(single: Single<T>): Single<T> =
        TODO("Similar to onAssembleSingle")

    override fun <T> onAssembleMaybe(maybe: Maybe<T>): Maybe<T> = 
        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: