This document discusses concurrency in Kotlin using coroutines. It provides a brief history of concurrency approaches including threads, futures, and reactive programming. It then introduces coroutines as Kotlin's solution for writing concurrent code in a sequential style using suspending functions and other coroutine primitives like launch, async, and channels. The document demonstrates how coroutines allow writing concurrent code that looks sequential and avoids callbacks through use of coroutines and suspending functions.

1. Concurrency in
Kotlin with coroutines
Jörn Dinkla (translated and extended edition of slides for a talk at para//el 2019)

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Feedback link in the chat!

7. 1985 1998
2004 2007 20192001 2010 2013 2016
Reactive
2017
Fork/Join
2011
Streams
CmplFut
201420041995
thread
2011
mutex
2014
par STL
2017
1.0
2016
1.3
2018

8. “A community of passionate individuals
whose purpose is to revolutionize
software design, creation and delivery,
while advocating for positive social change.”
We are
hiring ...

9. © https://www.flickr.com/photos/dougtone/

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13. !

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$ find . -name "*.kt" | xargs wc -l

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21. Java11
HttpClient

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23. Kotlin as
better Java !

24. Why so
low?

25. server [main thread]
Handler [thread] Handler [thread]
Start End
Web Web
Waiting
WaitingSleeping Sleeping

27. W C
Ncpu Ucpu W C Nthreads
8 1.0 0 1 8
8 1.0 1 1 16
8 1.0 1 2 12
8 1.0 2 1 24
CPU bound

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● Future
● CompletableFuture
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34. We are still
using
threads and
pools!

35. Chaining

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42. String!

43. Looks like
a build in
function

44. Internal
DSL

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46. starts CoroutineScope and
waits for all coroutines
Starts Coroutine async
like Thread.sleep()

47. runBlocking {...}
suspend

48. suspend
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● Suspendable function or lambda
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49. suspend
Refactor > Extract > Function
Ctrl+Alt+M

50. CoroutineScope
Refactor > Extract > Function
Ctrl+Alt+M

51. CoroutineScope
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○ Job
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○ SupervisorJob()
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52. launch
● launch Job
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Like a
thread?

53. async
● async Deferred<T>
Like a
future?

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55. Continuation
1991

56. Kotlin Evolution and Enhancement Process

57. state
resume
Simplification

58. CoroutineContext
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○ isActive()
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59. CoroutineContext

60. CoroutineDispatcher
● Dispatchers.Default
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● Dispatchers.IO
○ kotlinx.coroutines.io.parallelism
● Dispatchers.Main
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67. ● Channel(capacity)
○ capacity 0
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○ capacity unlimited
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○ capacity
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○ capacity conflated

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70. Kotlin’s
OO model

71. Caveat: experimental,
obsolete,
But newer version not
available

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74. Code is
straightforward
again!

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