The Pitfalls of Cancellation

1. ©2020 Wantedly, Inc. The Pitfalls of Cancellation Presentation Subtitle 2020/12/22 Masatoshi Kubode https://unsplash.com/photos/J8sh37XZ8ww
2. ©2020 Wantedly, Inc. ٱอग़խढ़ 8BOUFEMZ 8BOUFEMZ
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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?
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8. ©2020 Wantedly, Inc. ͋Δ೔ͷΫϥογϡϨϙʔτ JobCancellationException͕ݪҼ
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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֎
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
12. ©2020 Wantedly, Inc. JobCancellationExceptionৄղ ΋ͱ΋ͱJavaͷฒྻॲཧAPIͰ࢖ΘΕ͍ͯͨྫ֎
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
14. ©2020 Wantedly, Inc. Kotlinͷੈք Kotlinʹ͸ݕࠪྫ֎͕ͳ͍ catch(Throwable)͕ͪ͠ CoroutinesͰ͸ࠓճͷΑ͏ͳ໰୊ʹܨ͕Γ΍͍͢ cancel()ͯ͠໰୊ͳ͍͔ͱ͍͏ςετ͸;ͭ͏ॻ͔ͳ͍͠ɺ ݱঢ়͸ϓϩάϥϚ͕ؾΛ͚ͭΔ͔͠ͳ͍ʁ
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) } }
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