The Pitfalls of Cancellation

Transcript

1. ©2020 Wantedly, Inc.
   The Pitfalls of Cancellation
   Presentation Subtitle
   2020/12/22 Masatoshi Kubode
   https://unsplash.com/photos/J8sh37XZ8ww
   

   View Slide

2. ©2020 Wantedly, Inc.
   ٱอग़խढ़
   8BOUFEMZ
   8BOUFEMZ7JTJUͷ"OESPJEΞϓϦΛ։ൃ͍ͯ͠·͢ɻ
   ,PUMJO .BHJDUIF(BUIFSJOH
   UIJTUP4USJOH
   
   5XJUUFS
   !TXJ[@BSE
   (JU)VC
   !LVCPEF
   

   View Slide

3. ϖʔδλΠτϧ ϖʔδαϒλΠτϧ
   ©2020 Wantedly, Inc.
   $PSPVUJOFTͰى͖ͨΫϥογϡͷ࿩
   

   View Slide

4. ©2020 Wantedly, Inc.
   ͋Δ೔ͷΫϥογϡϨϙʔτ
   

   View Slide

5. ϖʔδλΠτϧ ϖʔδαϒλΠτϧ
   ©2020 Wantedly, Inc.
   
   

   View Slide

6. ©2020 Wantedly, Inc.
   ֘౰ίʔυ
   class FetchDiscoverPostsUseCaseImpl(
   private val discoverRepository: DiscoverRepository,
   ) : FetchDiscoverPostsUseCase {
   override suspend operator fun invoke(sectionId: DiscoverSectionId) {
   try {
   return discoverRepository.fetchDiscoverPosts(sectionId)
   } catch (@Suppress("TooGenericExceptionCaught") e: Throwable) {
   throw FetchDiscoverProjectsUseCase.Error(
   "Failed to fetch discover posts for section: $sectionId”,
   e
   )
   }
   }
   }
   ←ίϐϖͰTypoͯ͠Δ
   Repositoryͷྫ֎Λϥοϓͯ͠
   Rethrowͯ͠Δ͚ͩͳͷʹ
   ͳͥ?
   

   View Slide

7. ϖʔδλΠτϧ ϖʔδαϒλΠτϧ
   ©2020 Wantedly, Inc.
   4UBDL5SBDFΛΑ͘ݟΔ
   

   View Slide

8. ©2020 Wantedly, Inc.
   ͋Δ೔ͷΫϥογϡϨϙʔτ
   JobCancellationException͕ݪҼ
   

   View Slide

9. ϖʔδλΠτϧ ϖʔδαϒλΠτϧ
   ©2020 Wantedly, Inc.
   +PC$BODFMMBUJPO&YDFQUJPOͱ͸
   

   View Slide

10. ©2020 Wantedly, Inc.
    JobCancellationException
    https://atoulme.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.experimental/-job-cancellation-exception/index.html
    Job.cancel()͞Εͨͱ͖ʹ
    suspend͍ͯ͠Δؔ਺͔ΒThrow͞ΕΔ
    CoroutinesͷγεςϜతͳྫ֎
    

    View Slide

11. ©2020 Wantedly, Inc.
    ֘౰ίʔυ
    class FetchDiscoverPostsUseCaseImpl(
    private val discoverRepository: DiscoverRepository,
    ) : FetchDiscoverPostsUseCase {
    override suspend operator fun invoke(sectionId: DiscoverSectionId) {
    try {
    return discoverRepository.fetchDiscoverPosts(sectionId)
    } catch (@Suppress("TooGenericExceptionCaught") e: Throwable) {
    throw FetchDiscoverProjectsUseCase.Error(
    "Failed to fetch discover posts for section: $sectionId”,
    e
    )
    }
    }
    } ͭ·ΓɺCoroutinesͷγεςϜతͳྫ֎Λ
    ϥοϓͯ͠͠·͔ͬͨΒΫϥογϡͨ͠
    

    View Slide

12. ©2020 Wantedly, Inc.
    JobCancellationExceptionৄղ
    ΋ͱ΋ͱJavaͷฒྻॲཧAPIͰ࢖ΘΕ͍ͯͨྫ֎
    

    View Slide

13. ©2020 Wantedly, Inc.
    Javaͷੈք
    java.util.concurrent.Future#get()
    try {
    future.get();
    } catch (ExecutionException e) {
    e.printStackTrace();
    } catch (InterruptedException e) {
    e.printStackTrace();
    }
    CancellationException͸RuntimeException
    ͳͷͰ໌ࣔతͳcatchෆཁ
    CancellationΛcatchͪ͠Ό͏͜ͱ͕ى͖ͮΒ͍
    

    View Slide

14. ©2020 Wantedly, Inc.
    Kotlinͷੈք
    Kotlinʹ͸ݕࠪྫ֎͕ͳ͍
    catch(Throwable)͕ͪ͠
    CoroutinesͰ͸ࠓճͷΑ͏ͳ໰୊ʹܨ͕Γ΍͍͢
    cancel()ͯ͠໰୊ͳ͍͔ͱ͍͏ςετ͸;ͭ͏ॻ͔ͳ͍͠ɺ
    ݱঢ়͸ϓϩάϥϚ͕ؾΛ͚ͭΔ͔͠ͳ͍ʁ
    

    View Slide

15. ©2020 Wantedly, Inc.
    Ͳ͏͢΂͖͔
    launch {
    try {
    codeThatCanThrowExceptions()
    //
    // } catch (e: Throwable) {
    // } catch (e: Exception) {
    // } catch (e: RuntimeException) {
    // } catch (e: IllegalStateException) {
    // } catch (e: CancellationException) {
    } catch (e: SpecificException) { //
    throw MyException(e)
    }
    }
    // OR
    launch {
    try {
    codeThatCanThrowExceptions()
    } catch (e: Throwable) {
    throw e as? CancellationException ?: MyException(e)
    }
    }
    

    View Slide

16. ©2020 Wantedly, Inc.
    w ,PUMJOʹ͸ݕࠪྫ֎͕ͳ͍ͷͰࡶʹ͕͕ͪͩ͠ɺ
    $PSPVUJOFTͰ5PP(FOFSJDͳDBUDI͸ةݥ
    w DBUDI͔ͨͬͨ͠Β$BODFMMBUJPO͸SFUISPX
    w ΋͘͠͸$PSPVUJOF&YDFQUJPO)BOEMFSΛ࢖͏
    w -JOU͸ແࢹ͠ͳ͍
    ·ͱΊ
    

    View Slide

17. ϖʔδλΠτϧ ϖʔδαϒλΠτϧ
    ©2020 Wantedly, Inc.
    
    

    View Slide