Design Reactive Apps in Kotlin

Transcript

1. DESIGN REACTIVE APPS IN KOTLIN
2. GRAB STEPAN GONCHAROV
3. 3 BACKGROUND ▸ 9+ years in Android development ▸ Exploring Kotlin since 2014 ▸ Organiser of Kotlin User Group Singapore ▸ Using Kotlin in production app since 2016
4. 4 WHAT THIS TALK IS ABOUT ▸ How to design your app components by example ▸ How Kotlin would help you with that ▸ Discussed solutions could be applied for most of the languages on many platforms
5. 5 PLAN ▸ Kotlin ▸ Reactive Extensions ▸ Problem - solution ▸ Extending solution to handle more scenarios
6. 6 KOTLIN ▸ Programming language by JetBrains ▸ Officially supported by Google ▸ Could be complied for Android/JVM/JS/Native platforms ▸ Supports lots of modern programming concepts ▸ Looks a lot like Swift
7. 7 REACTIVE EXTENSIONS ▸ Modern approach to async programming ▸ Extremely popular in Android community ▸ Supports by most of modern programming languages
8. SOLVE ONCE… USE EVERYWHERE
9. PROBLEM 1: RUNNING DUPLICATED JOBS
10. 9 SCENARIOS ▸ Save form:
 Duplicated requests caused by multiple clicks
11. 10 IS IT SAME JOB? interface Act { val id: String } ▸ Should have ID
12. KOTLIN FACTS: INTERFACE COULD HAVE PROPERTIES
13. 12 HOW? ▸ Requirements should be split into small pieces ▸ Implementation should be split into small pieces
14. 13 IS ID ENOUGH? ▸ How we would check is job with same ID is running? ▸ Who will cancel duplicated jobs? ▸ How to prevent jobs from being launched without checks
15. 14 ABSTRACT EXECUTOR: AGENT ▸ Checks if job is in progress ▸ Start execution if no jobs with same id is running ▸ Provides error handling callbacks ▸ Cancel current execution
16. 15 ABSTRACT EXECUTOR: AGENT interface Agent { fun execute(executable: Act, e: (Throwable) -> Unit = ::logError) fun cancel(id: String) fun cancelAll() }
17. IMPLEMENTATION TIME
18. 17 interface Act { val id: String } class CompletableAct( override val id: String, override val completable: Completable ) : Act class SingleAct<T : Any>( override val id: String, override val single: Single<T> ) : Act ABSTRACT EXECUTOR: AGENT
19. class AgentImpl : Agent { val map = ConcurrentHashMap<String, Disposable>() fun execute(act: Act, e: (Throwable) -> Unit) = when { map.containsKey(act.id) -> log("${act.id} - in progress") else -> startExecution(act, e) .apply { log(“${act.id} - Started”) } } … AGENT IMPLEMENTATION 18
20. class AgentImpl : Agent { … fun startExecution(act: Act, e: (Throwable) -> Unit) { val removeFromMap = { map.remove(act.id) } when (act) { is CompletableAct -> act.completable .doFinally(removeFromMap) .subscribe({}, e) is SingleAct<*> -> act.single .doFinally(removeFromMap) .subscribe({}, e) else -> throw IllegalArgumentException() }.let { map.put(act.id, it) } } } AGENT IMPLEMENTATION 19
21. KOTLIN FACTS: KEEP FUNCTION AS LAST ARGUMENT TO ALLOW SPECIAL SYNTAX
22. 21 A BIT OF EXTENSIONS fun Completable.toAct(id: String): Act = CompletableAct(id, this) fun <T: Any> Single<T>.toAct(id: String): Act = SingleAct(id, this)
23. KOTLIN FACTS: ANY CLASS COULD BE EXTENDED
24. 23 RESULT val a = AgentImpl() a.execute(Completable.timer(2, SECONDS).toAct("Hello")) a.execute(Completable.timer(2, SECONDS).toAct("Hello")) a.execute(Completable.timer(2, SECONDS).toAct("Hello")) Hello - Act Started Hello - Act Duplicate Hello - Act Duplicate Hello - Act Finished
25. PROBLEM 2 WHICH JOB WE NEED TO CANCEL?
26. 25 SCENARIOS ▸ Refresh:
 Cancel second refresh call ▸ User profile update:
 Cancel first update
27. 26 STRATEGIES interface StrategyHolder { val strategy: Strategy } sealed class Strategy object KillMe : Strategy() object SaveMe : Strategy()
28. KOTLIN FACTS: SEALED CLASSES ARE COOL
29. 28 MODIFY EXISTING COMPONENTS interface Act : StrategyHolder { val id: String } class CompletableAct( override val id: String, override val completable: Completable, override val strategy: Strategy = SaveMe ) : Act
30. 29 STRATEGIES override fun execute(act: Act, e: (Throwable) -> Unit) = when { map.containsKey(act.id) -> when (act.strategy) { KillMe -> { cancel(act.id) startExecution(act, e) } SaveMe -> log("${act.id} - Act duplicate") } else -> startExecution(act, e) }
31. 30 RESULT val a = AgentImpl() a.execute(Completable.timer(2, SECONDS) .toAct(“Hello”, KillMe)) a.execute(Completable.timer(2, SECONDS) .toAct(“Hello”, KillMe)) a.execute(Completable.timer(2, SECONDS) .toAct(“Hello”, KillMe)) Hello - Act Started Hello - Act Canceled Hello - Act Started Hello - Act Canceled Hello - Act Started Hello - Act Finished
32. 31 WHAT WE ACHIEVED SO FAR? ▸ Could compare Act’s ▸ Actor could decide if Act’s needs to run based on id and strategy ▸ Subscriptions managed by Agent ▸ Errors handled by Agent
33. PROBLEM 3 ID IS NOT ENOUGH
34. 33 SCENARIOS ▸ Like/dislike:
 dislike should cancel like
35. 34 GROUPS AND GROUP STRATEGIES interface GroupStrategyHolder { val groupStrategy: GroupStrategy val groupKey: String } sealed class GroupStrategy object Default : GroupStrategy() object KillGroup : GroupStrategy()
36. 35 GROUPS AND GROUP STRATEGIES interface Act : StrategyHolder, GroupStrategyHolder { val id: String } class CompletableAct( override val id: String, override val completable: Completable, override val strategy: Strategy = SaveMe, override val groupStrategy: GroupStrategy = Default override val groupKey: String = “” ) : Act
37. 36 AGENT IMPLEMENTATION typealias ActKey = String typealias GroupKey = String typealias GroupMap = ConcurrentHashMap<ActKey, Disposable> …
 
 private val groupsMap = ConcurrentHashMap<GroupKey, GroupMap>() override fun execute(act: Act, e: (Throwable) -> Unit) { val actsMap = groupsMap[act.groupKey] ?: ConcurrentHashMap<ActKey, Disposable>() .apply { groupsMap[act.groupKey] = this } if (act.groupStrategy == KillGroup) actsMap.values.forEach { it.dispose() } … }
38. KOTLIN FACTS: WHEN THINGS GETS MESSY USE TYPE ALIAS
39. 38 RESULT val a = AgentImpl() a.execute(Completable.timer(2, SECONDS).toAct( id = "Like", groupStrategy = KillGroup, groupKey = "Like-Dislike-PostId-1234")) a.execute(Completable.timer(2, SECONDS).toAct( id = "Dislike", groupStrategy = KillGroup, groupKey = "Like-Dislike-PostId-1234")) a.execute(Completable.timer(2, SECONDS).toAct( id = "Like", groupStrategy = KillGroup, groupKey = "Like-Dislike-PostId-1234")) Like - Act Started Like - Act Canceled Dislike - Act Started Dislike - Act Canceled Like - Act Started Like - Act Finished
40. KOTLIN FACTS: WHEN THINGS GETS MESSY USE NAMED ARGS
41. 40 PAST VIEW MODEL / PRESENTER START JOBS SUBSCRIPTIONS MANAGEMENT CODE DUPLICATION EXECUTION STRATEGIES LOGIC JOB GROUPS MANAGEMENT VIEW STATE LIFECYCLE
42. 41 FUTURE VIEW MODEL / PRESENTER AGENT START JOBS SUBSCRIPTIONS MANAGEMENT LIFECYCLE JOB GROUPS MANAGEMENT ACT’S VIEW STATE EXECUTION STRATEGIES DECLARATIONS
43. EXTENSIONS
44. 43 SUPERCHARGE YOUR AGENT ▸ Lifecycle ▸ Persistency ▸ Plugins ▸ Metrics
45. 44 LIFECYCLE class AgentImpl(lifecycle: Lifecycle) : Agent { init { lifecycle.doOnDestroy { cancelAll() } } …
46. 44 PLUGINS FOR AGENTS override fun execute(executable: Act, eh: (Throwable) -> Unit): Mission { processGroupStrategy(executable) return processActStrategy(executable) }
47. 45 PERSISTENCY ▸ Code inside separate classes ▸ Handle execution error ▸ Save Act to DB ▸ Restore Act from DB ▸ Act chains
48. 46 METRICS ▸ Realtime monitor for Agent ▸ How many acts running ▸ Execution time ▸ Errors
49. THANK YOU!
50. WE ARE HIRING! @stepango stepan.goncharov@grab.com
51. QUESTIONS Source code: github.com/stepango/akt