This document summarizes a meetup about asynchronous programming in Kotlin using coroutines. It discusses how coroutines allow direct-style asynchronous code by suspending coroutines instead of blocking threads. Coroutines appear like regular blocking code but are lightweight like threads. Suspending functions can pause and return values later. Demos show using coroutines with builders, contexts, and channels for asynchronous programming compared to callbacks and RxJava.

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Rhein-Neckar Dev Meetup #1

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Asynchronous progamming in Kotlin with Coroutines
🍕 🍕 🍕
Tensorflowing like a pro - without a clue

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Coroutines
Asynchronous programming in Kotlin

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How programming works
Intro
Do something (create a resource)
↓
Wait (for completion)
↓
Do something (send it to backend)
↓
Wait (for the response)
↓
Do something (process response or try again)
↓
…

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Dealing with long running tasks
Asynchronicity
- Direct style
- max 16 ms
- Blocking the main Thread
- Callback
- Error Handling
- Callback Hell
- Futures (RxJava, Promises, …)
- Idea: we wrap the result
- Pro: nice code, errors, good looking
- cons: complex
- Coroutines
- Direct style

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What is a Coroutine?
- It’s an instance of a suspendable computation
- General concept was already created in 1958
- Similar to a very lightweight Thread – cheap in creation
- Looks like regular blocking code
- Coroutines give us a way to write code that feels imperative, even if it is asynchronous.

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Suspend functions
- A function ‘super powers’
- It’s a function which can suspend and return a value later on

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Suspend functions II
- Suspension points
- Many things work out-of-the box
- Loops
- Exceptions
- Higher-Order-Functions
- …

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suspension functions are designed to
imitate sequential behavior by default

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Setup

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Demo I
- Sample + Performance

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https://www.slideshare.net/elizarov/deep-dive-into-coroutines-on-jvm-kotlinconf-2017
Coroutines in detail

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Reuse closure / state object
State Machine vs Callbacks
Easier loop

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Suspending functions cannot be invoked from
regular functions
• launch (fire and forget)
• async (and await)
• Returns a Deferred
• runBlocking
• Not keywords but functions!
Coroutine Builder

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Demo II
– Coroutine Builders

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Coroutine Context
- *without*
- UI
- CommonPool
- Unconfined

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Demo III
– Channels and Actors
- Comparison RX

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Questions?
Pizza?

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Links & References
- Coroutines guide Informal
- https://github.com/Kotlin/kotlin-coroutines/blob/master/kotlin-coroutines-informal.md
- Coroutine guide reactive
- https://github.com/Kotlin/kotlinx.coroutines/blob/master/reactive/coroutines-guide-reactive.md
- Deep dive into Coroutines on JVM, KotlinConf 2017 – Roman Elizarov
https://www.slideshare.net/elizarov/deep-dive-into-coroutines-on-jvm-kotlinconf-2017
- Images from https://www.pexels.com