Channels N Stuff

Let's dig into kotlin coroutines channels.
Thats where it started, it ended up with a crash-course in coroutines, synchronisation primitives, deferred, channels and Flow.
Also trying to answer the question - will it replace Rx?

Transcript

1. 
 Channels N Stuff Bob
 Dahlberg
2. Bob Dahlberg Android at Bonnier News
 Challenge Accepted Kotlin Stockholm Tech Group GDG Stockholm Android Who’s Bob?
 - Building software
 - CrossFit enthusiast
 - Father of one
 - Arranging meetups
 - Loves a good challenge!
3. Background ActionScript (Flash) Been there! Done that! Moved … 

4. Background ActionScript (Flash) Been there! Done that! Moved … For all of you born after the millennium, flash was king!
5. Background ActionScript (Flash)
6. Background ActionScript Android (Java) Started something new since flash was about to be abandoned. Went native with Java rather than cross platform: 
 (ActionScript, Xamarin, PhoneGap)

7. Background ActionScript Android (Java) Did a lot of threading, networking, image loading with different solutions. Built my own async task handler.
8. Background ActionScript Android Rx Did a lot of threading, networking, image loading with different solutions. Built my own async task handler. Ended up doing a lot of Rx.
9. Background ActionScript Android Rx Scala Learned Scala and tried to build Android with it..
10. Background ActionScript Android Rx Scala 
 Learned Scala and tried to build Android with it.. It’s plausible.
 But you rather die a little.
11. Background ActionScript Android Rx Scala Kotlin Found Kotlin in 2015 and it blended almost seamlessly with Java.

12. Background ActionScript Android Rx Scala Kotlin So why all this about my past?
13. Background ActionScript - Asynchronous Android - Asynchronous Rx - Asynchronous Scala. - Functional Kotlin - Functional I’m raised in an asynchronous, callback world. With strong beliefs in reactive and functional idioms. Even before I knew it.
14. Background ActionScript - Asynchronous Android - Asynchronous Rx - Asynchronous Scala. - Functional Kotlin - Functional Cause of that coroutines are hard for my brain to grasp.
15. Coroutines
16. Coroutines Lightweight threads Conceptually the same as threads. - Offload async work on them
 - Specific ways of communication
17. Coroutines Lightweight threads Structured 
 Structured concurrency “An outer coroutine does not complete until all the coroutines launched in its scope complete” 
 
 
 in its scope
18. Coroutines Lightweight threads Structured
19. Coroutines Lightweight threads Structured
20. Coroutines Lightweight threads Structured
21. Coroutines Lightweight threads Structured
22. Coroutines Lightweight threads Structured Suspend 
 Coroutines are built by suspending functions. They suspend the current scope until done.
23. Coroutines Lightweight threads Structured Suspend
24. Coroutines Lightweight threads Structured Suspend
25. Coroutines Lightweight threads Structured Suspend
26. Coroutines Lightweight threads Structured Suspend Sequential 
 Coroutines are sequential by default. Non blocking, asynchronous.
 But not concurrent.
27. Coroutines Lightweight threads Structured Suspend Sequential
28. Coroutines Lightweight threads Structured Suspend Sequential Dispatchers “The coroutine context includes a coroutine dispatcher that determines what thread or threads the corresponding coroutine uses for its execution.”
29. Coroutines Lightweight threads Structured Suspend Sequential Dispatchers
30. Coroutines Lightweight threads Structured Suspend Sequential Dispatchers
31. Coroutines Lightweight threads Structured Suspend Sequential Dispatchers Dispatchers.Default - 8 threads
 Dispatchers.IO - 64 threads
 Dispatchers.Main - 0 or 1 threads
32. Coroutines Lightweight threads Structured Suspend Sequential Dispatchers Dispatchers.Default - 8 threads
 Dispatchers.IO - 64 threads
 Dispatchers.Main - 0 or 1 threads On this machine!
33. Coroutines Comparison
34. Comparison Callbacks
35. Comparison Callbacks Rx
36. Comparison Callbacks Rx Coroutines
37. So are coroutines replacing Rx?!
38. So are coroutines replacing Rx?! Nope!
39. So are coroutines replacing Rx?! Nope! It can replace some. 
 But coroutines is not reactive streams.
40. Coroutines Sharing is caring
41. Communication Shared mutable state 
 Still something that should be handled with extreme caution! Coroutines gives you nothing new on that matter.
42. Communication Shared mutable state launch vs async Both launch and async coroutine builders returning a job for the calling scope to control 
 (cancel - join).
43. Communication Shared mutable state launch vs async
44. Communication Shared mutable state launch vs async But async gives us a bit more.
45. Communication Shared mutable state launch vs async Deferred
46. Communication Shared mutable state launch vs async Deferred
47. Communication Shared mutable state launch vs async Deferred
48. Communication Shared mutable state launch vs async Deferred
49. Communication Shared mutable state launch vs async Deferred Order
50. Communication Shared mutable state launch vs async Deferred Order
51. Communication Shared mutable state launch vs async Deferred Order
52. Communication Shared mutable state launch vs async Deferred Order
53. Communication Shared mutable state launch vs async Deferred Order
54. Communication Shared mutable state launch vs async Deferred Order Streams
55. Communication Shared mutable state launch vs async Deferred Order Streams
56. Channels
57. Channels Definition “Deferred values provide a convenient way to transfer a single value between coroutines. 
 
 Channels provide a way to transfer a stream of values.”
58. Channels Definition
 Streams revisited
59. Channels Definition
 Streams revisited
60. Channels Definition
 Streams revisited
61. Channels Definition
 Streams revisited Order revisited
62. Channels Definition
 Streams revisited Order revisited
63. Channels Definition
 Streams revisited Order revisited
64. Channels Definition
 Streams revisited Order revisited
65. Channels Definition
 Streams revisited Order revisited
66. Channels Definition
 Streams revisited Order revisited Order revisited 2
67. Channels Definition
 Streams revisited Order revisited Order revisited 2 Order revisited 3
68. Channels Definition
 Streams revisited Order revisited Order revisited 2 Order revisited 3 Plain order of execution should not be handled by channels.
69. Channels Definition
 Streams revisited Order revisited Order revisited 2 Order revisited 3 But Channels are synchronization primitives…
70. Channels Definition
 Streams revisited Order revisited Order revisited 2 Order revisited 3 But Channels are synchronization primitives… So there must be some order!
71. Channels Definition
 Streams revisited Order revisited Order revisited 2 Order revisited 3 Order - Producer / Consumer
72. Channels Definition
 Streams revisited Order revisited Order revisited 2 Order revisited 3 Order - Producer / Consumer
73. Channels Definition
 Streams revisited Order revisited Order revisited 2 Order revisited 3 Order - Producer / Consumer
74. Channels Definition
 Streams revisited Order revisited Order revisited 2 Order revisited 3 Order - Producer / Consumer
75. Channels Definition
 Streams revisited Order revisited Order revisited 2 Order revisited 3 Order - Producer / Consumer Experimental
76. Channels Definition
 Streams revisited Order revisited Order revisited 2 Order revisited 3 Order - Producer / Consumer Experimental
77. Channels Definition
 Streams revisited Order revisited Order revisited 2 Order revisited 3 Order - Producer / Consumer Experimental A friend once told me that if it’s on a single line it can’t be bad code.
78. Channels Will it terminate?
79. Will it terminate
80. Will it terminate
81. Will it terminate
82. Will it terminate
83. Will it terminate
84. Gotchas
85. Gotchas Send is suspending
86. Gotchas Send is suspending Buffer
87. Gotchas Send is suspending Buffer Rendezvous
88. Gotchas Send is suspending Buffer Rendezvous Unlimited
89. Gotchas Send is suspending Buffer Rendezvous Unlimited Conflated
90. Gotchas Send is suspending Buffer Rendezvous Unlimited Conflated Channels are hot
91. Channels “Primitive” usages
92. Channels Fan out One producer, many consumers.
93. Channels Fan out
94. Channels Fan out
95. Channels Fan out Fan in One consumer, many producers.
96. Channels Fan out Fan in
97. Channels Fan out Fan in
98. Channels Fan out Fan in FIFO Channels respect the order of invocations from different coroutines. Elements are received in a “first in first out” order.
99. Channels Fan out Fan in FIFO Channels respect the order of invocations from different coroutines. Elements are received in a “first in first out” order.
100. Channels Builders and Types of Channels
101. Creating Channel The simple Channel() standard and simple. Also ReceiverChannel and SendChannel for specific usage
102. Creating Channel Broadcast? As seen especially in the fan out example where we have many consumers and one producer, kinda like RX. But there’s only one receiving each element… can we broadcast?
103. Creating Channel BroadcastChannel As seen especially in the fan out example where we have many consumers and one producer, kinda like RX. But there’s only one receiving each element… can we broadcast? Yes, we can!
104. Creating Channel BroadcastChannel
 ConflatedBroadcastChannel Now we can also have only the most recent sent value. Did anyone say BehaviorSubject?
105. Creating Channel BroadcastChannel
 ConflatedBroadcastChannel Operators? To really become a force to compare to Rx we must have some operators!
106. Creating Channel BroadcastChannel
 ConflatedBroadcastChannel Operators 
 .distinct
 
 .filter
 
 .flatMap
 
 .reduce
107. Creating Channel BroadcastChannel
 ConflatedBroadcastChannel Operators .any
 .distinct
 .drop
 .filter
 .first
 .flatMap
 .minBy
 .reduce
108. Creating Channel BroadcastChannel
 ConflatedBroadcastChannel Operators That’s awesome! .any
 .distinct
 .drop
 .filter
 .first
 .flatMap
 .minBy
 .reduce And 87 others.
109. Is it a replacement for Rx?
110. Is it a replacement for Rx? Let’s investigate the signs.
111. Creating Channel BroadcastChannel
 ConflatedBroadcastChannel Operators That’s awesome! .any
 .distinct
 .drop
 .filter
 .first
 .flatMap
 .minBy
 .reduce And 87 others.
112. Creating Channel BroadcastChannel
 ConflatedBroadcastChannel Operators That’s awesome! .any
 .distinct
 .drop
 .filter
 .first
 .flatMap
 .minBy
 .reduce And 87 others. Experimental
113. Creating Channel BroadcastChannel
 ConflatedBroadcastChannel Operators That’s awesome! .any
 .distinct
 .drop
 .filter
 .first
 .flatMap
 .minBy
 .reduce And 87 others. DEPRECATED
114. Is it a replacement for Rx? Nope
115. Channels are synchronization primitives
116. Actor Should match Like actors that encapsulates a shared mutable state. Their mailbox should be a good fit for channels!
117. Actor Should match Actor builder
118. Actor Should match Actor builder
119. Actor Should match Actor builder
120. ObsoleteApi Meaning it will be removed
121. Why?
122. Why? Why is everything deprecated or obsolete?
123. Why? Actor builder “Note: This API will become obsolete in future updates with introduction of complex actors.”
124. Why? Actor builder All the operators “Channel operators are deprecated in favour of Flow and will be removed in 1.4”
125. What is Flow?
126. Flow Cold streams Cold streams, some using channels to communicate.
127. Flow Cold streams On coroutines Running on coroutines and benefits from not having subscribers and cleaning up duties.
128. Flow Cold streams On coroutines Extensible Loads of operators built in 
 and extremely easy to add 
 via extension functions.
129. Flow Cold streams On coroutines Extensible Channels Giving them the benefit of back pressure support easy as that.
130. Is it a replacement for Rx?
131. Is it a replacement for Rx?
132. Is it a replacement for Rx? Yup! (IMHO)
133. To sum up
134. Sum up Coroutines 
 Not a replacement of Rx

135. Sum up Coroutines Channels 
 Not a replacement of Rx
 Not a replacement of Rx
136. Sum up Coroutines Channels Flow 
 
 Not a replacement of Rx
 Not a replacement of Rx 
 A replacement of Rx
137. Take aways Coroutines It’s one of the cleanest ways to work with asynchronous code. Even though I’m still having issues to wrap my head around the new way of thinking. You know, old dogs!
138. Take aways Coroutines Deferred 
 
 A synchronisation primitive solving the output of one value or one object from a coroutine.

139. Take aways Coroutines Deferred Channel A synchronisation primitive solving the output of a stream of values or objects from one or several coroutine to one or several coroutines.

140. Take aways Coroutines Deferred Channel Hot streams
141. Take aways Coroutines Deferred Channel Buffering strategies
142. Take aways Coroutines Deferred Channel Producer - Consumer
143. Take aways Coroutines Deferred Channel Actors
144. Take aways Coroutines Deferred Channel Flow The next thing in asynchronous programming with Kotlin that will really give other reactive stream solutions a match.
145. Take aways Coroutines Deferred Channel Flow Kotlin Conf: - ASYNCHRONOUS DATA STREAMS 
 WITH KOTLIN FLOW
 - MIGRATING FROM RXJAVA TO FLOW
 - INTRO TO CHANNELS AND FLOW
146. Thank you! Kotlin Conf: - ASYNCHRONOUS DATA STREAMS 
 WITH KOTLIN FLOW
 - MIGRATING FROM RXJAVA TO FLOW
 - INTRO TO CHANNELS AND FLOW