Hi can someone explain why exception is not consumed by try

Question

Hi can someone explain why exception is not consumed by try catch Steps to reproduce fast clicks on button ```class MainActivity AppCompatActivity CoroutineScope by MainScope private val singleThread = this + newSingleThreadContext SingleThread override fun onCreate savedInstanceState Bundle Timber plant Timber DebugTree super onCreate savedInstanceState setContentView R layout activity main val api = PokemonApi createApi button setOnClickListener singleThread launch try val names = async api getPokemonNames val types = async api getPokemonTypes val stages = async api getPokemonStages val owners = async api getPokemonOwners names join types join stages join owners join catch e UnknownHostException exception is not consumed val crashHandler = Thread getDefaultUncaughtExceptionHandler val exceptionHandler = Thread UncaughtExceptionHandler thread exception gt try Timber tag UncaughtException e exception finally crashHandler uncaughtException thread exception Thread setDefaultUncaughtExceptionHandler exceptionHandler interface PokemonApi GET names suspend fun getPokemonNames GET types suspend fun getPokemonTypes GET stages suspend fun getPokemonStages GET owners suspend fun getPokemonOwners companion object fun createApi PokemonApi return Retrofit Builder baseUrl build create PokemonApi class java ``` stacktrace ```E UncaughtException UnknownHostException Unable to resolve host No address associated with hostname at Inet6AddressImpl lookupHostByName Inet6AddressImpl java 156 at Inet6AddressImpl lookupAllHostAddr Inet6AddressImpl java 103 at InetAddress getAllByName InetAddress java 1152 at okhttp3 Dns$Companion$DnsSystem lookup Dns kt 49 at okhttp3 internal connection RouteSelector resetNextInetSocketAddress RouteSelector kt 164 at okhttp3 internal connection RouteSelector nextProxy RouteSelector kt 129 at okhttp3 internal connection RouteSelector next RouteSelector kt 71 at okhttp3 internal connection ExchangeFinder findConnection ExchangeFinder kt 199 at okhttp3 internal connection ExchangeFinder findHealthyConnection ExchangeFinder kt 108 at okhttp3 internal connection ExchangeFinder find ExchangeFinder kt 76 at okhttp3 internal connection RealCall initExchange$okhttp RealCall kt 245 at okhttp3 internal connection ConnectInterceptor intercept ConnectInterceptor kt 32 at okhttp3 internal http RealInterceptorChain proceed RealInterceptorChain kt 100 at okhttp3 internal cache CacheInterceptor intercept CacheInterceptor kt 82 at okhttp3 internal http RealInterceptorChain proceed RealInterceptorChain kt 100 at okhttp3 internal http BridgeInterceptor intercept BridgeInterceptor kt 83 at okhttp3 internal http RealInterceptorChain proceed RealInterceptorChain kt 100 at okhttp3 internal http RetryAndFollowUpInterceptor intercept RetryAndFollowUpInterceptor kt 74 at okhttp3 internal http RealInterceptorChain proceed RealInterceptorChain kt 100 at okhttp3 internal connection RealCall getResponseWithInterceptorChain$okhttp RealCall kt 197 at okhttp3 internal connection RealCall$AsyncCall run RealCall kt 502 at java util concurrent ThreadPoolExecutor runWorker ThreadPoolExecutor java 1167 at java util concurrent ThreadPoolExecutor$Worker run ThreadPoolExecutor java 641 at java lang Thread run Thread java 919 Suppressed UnknownHostException Unable to resolve host No address associated with hostname 24 more Caused by android system GaiException android getaddrinfo failed EAI NODATA No address associated with hostname at libcore io Linux android getaddrinfo Native Method at libcore io ForwardingOs android getaddrinfo ForwardingOs java 74 at libcore io BlockGuardOs android getaddrinfo BlockGuardOs java 200 at libcore io ForwardingOs android getaddrinfo ForwardingOs java 74 at Inet6AddressImpl lookupHostByName Inet6AddressImpl java 135 23 more Caused by android system GaiException android getaddrinfo failed EAI NODATA No address associated with hostname at libcore io Linux android getaddrinfo Native Method at libcore io ForwardingOs android getaddrinfo ForwardingOs java 74 at libcore io BlockGuardOs android getaddrinfo BlockGuardOs java 200 at libcore io ForwardingOs android getaddrinfo ForwardingOs java 74 at Inet6AddressImpl lookupHostByName Inet6AddressImpl java 135 23 more E AndroidRuntime FATAL EXCEPTION SingleThread Process com example myapplication PID 24936```

streetsofboston · Answer

Have you installed a CoroutineException handling in the top most CoroutineScope <https medium com the kotlin chronicle coroutine exceptions 3378f51a7d33>

Andrey Stepankov · Answer

Handle do not help me I think that crash in same reason with <https jakewharton com exceptions and proxies and coroutines oh my >

louiscad · Answer

Yes I can explain you need to wrap all your calls to `async` in a local `coroutineScope` and put your `try` block around it Without it the `launch` gets the crash cancels all children coroutines and crashes its parent scope

streetsofboston · Answer

But wouldn t calling `await ` on async calls `Deferred lt T gt ` results be sufficient

Andrey Stepankov · Answer

Hm it works One moment i need to check it on real project

louiscad · Answer

< streetsofboston> You need to understand structured concurrency A crashing child coroutine i e unhandled exception that is not a `CancellationException` will cancel its parent scope So if you want to handle errors without crashing the parent scope you need a middle scope `coroutineScope ` and catch exceptions throwables around it The intent of the behavior is to cancel fast work in the same scope if one fails to avoid pursuing unneeded work that cannot be used as a part already failed

streetsofboston · Answer

But installing a `SupervisorJob` MainActivity s CoroutineScope in the should be sufficient to not cancel the MainActivity s CoroutineScope after a failure happens In my opinion if `names` fails you want the others `types` `stages` etc to be cancelled as well

streetsofboston · Answer

And I do understand structure concurrency slightly smiling face

Andrey Stepankov · Answer

So in case like that I will get error on launch coroute ```launch try getCats catch no op getCats will throw UnknownHostException suspend fun callApi = httpClient getCats ```

louiscad · Answer

If it s an Activity you should use `lifecycleScope` extension brought by AndroidX Lifecycle runtime KTX 2 2 0+ that already uses a `SupervisorJob` for the case where you use independant `async` where one can fail while letting the other still be useful on its own

Andrey Stepankov · Answer

No its not an activity its `MainScope + newSingleThreadContext SingleThread `

streetsofboston · Answer

``` val names = async api getPokemonNames val types = async api getPokemonTypes val stages = async api getPokemonStages val owners = async api getPokemonOwners val listOfResults = listOf names types stages owners awaitAll or call `await ` on each one individually depending on your use case ```

streetsofboston · Answer

Your MainActivity implements a CoroutineScope But as Louis said use the `lifecycleScope` instead It is all set up correctly already `lifecycleScope launch ` slightly smiling face

Andrey Stepankov · Answer

Yeah All you advice works well with example Samething another is wrong on real project Thx

Andrey Stepankov · Answer

Oh face palm As result is it my bad I forget to add try catch in another place Place with flow and async works perfectly