My function is quite straightforward,
Main Thread: Initializes a variable ->
Background Thread: Fire network request, assign the result back to the previous variable ->
Main Thread: Display that variable
Code below:
suspend fun createCity(context: Context, newCity: MutableLiveData<NewIdea>, mapBody: Map<String, String>, token: String) {
lateinit var response: NewIdea
try {
withContext(Dispatchers.IO) {
val map = generateRequestBody(mapBody)
response = webservice.createIdea(tripId, map, "Bearer $token")
getTrip(context, token)
}
} catch (e: Exception) {
Log.e(TAG, e.message)
}
newCity.value = response
}
But sometimes (it only happened 2 times actually) crashlytics reports crash for this line newCity.value = response
Fatal Exception: kotlin.UninitializedPropertyAccessException: lateinit property response has not been initialized
I don't really understand how that can happen.
Is this the correct way to return value from coroutine function?
thanks
Well if try block fails, it might happen that the lateinit variable isn't set at all. You should put the ui update code inside the try block as well, and handle the Exception separately:
Sidenote: withContext is well-optimized to return values, so you can make use of it.
suspend fun createCity(context: Context, newCity: MutableLiveData<NewIdea>, mapBody: Map<String, String>, token: String) {
try {
val response: NewIdea = withContext(Dispatchers.IO) {
val map = generateRequestBody(mapBody)
// does createIdea() first store it in var, then does getTrip(), then returns the result of createIdea() stored previously
webservice.createIdea(tripId, map, "Bearer $token").also { getTrip(context, token) } // ^withContext
}
newCity.value = response
} catch (e: Exception) {
Log.e(TAG, e.message)
}
}
A quick tip (optional): You can wrap the UI updating code with a withContext that dispatches the work to Dispatchers.Main when not running in main thread, while if running in main do nothing:
withContext(Dispatchers.Main.immediate) {
val response: NewIdea = withContext(Dispatchers.IO) {
val map = generateRequestBody(mapBody)
// does createIdea() first store it in var, then does getTrip(), then returns the result of createIdea() stored previously
webservice.createIdea(tripId, map, "Bearer $token").also { getTrip(context, token) } // ^withContext
}
newCity.value = response
}
Related
I am trying to retrieve the base url from my proto datastore to be used to initialize my ktor client instance I know how to get the data from the datastore but I don't know how to block execution until that value is received so the client can be initialized with the base url
So my ktor client service asks for a NetworkURLS class which has a method to return the base url
Here is my property to retrieve terminalDetails from my proto datastore
val getTerminalDetails: Flow<TerminalDetails> = cxt.terminalDetails.data
.catch { e ->
if (e is IOException) {
Log.d("Error", e.message.toString())
emit(TerminalDetails.getDefaultInstance())
} else {
throw e
}
}
Normally when I want to get the values I would do something like this
private fun getTerminalDetailsFromStore() {
try {
viewModelScope.launch(Dispatchers.IO) {
localRepository.getTerminalDetails.collect {
_terminalDetails.value = it
}
}
} catch(e: Exception) {
Log.d("AdminSettingsViewModel Error", e.message.toString()) // TODO: Handle Error Properly
}
}
but in my current case what I am looking to do is return terminalDetails.backendHost from a function and that where the issue comes in I know I need to use a coroutine scope to retrieve the value so I don't need to suspend the function but how to a prevent the function returning until the coroutine scope has finished?
I have tried using async and runBlocking but async doesn't work the way I would think it would and runBlocking hangs the entire app
fun backendURL(): String = runBlocking {
var url: String = "localhost"
val job = CoroutineScope(Dispatchers.IO).async {
repo.getTerminalDetails.collect {
it.backendHost
}
}
url
}
Can anyone give me some assistance on getting this to work?
EDIT: Here is my temporary solution, I do not intend on keeping it this way, The issue with runBlocking{} turned out to be the Flow<T> does not finish so runBlocking{} continues to block the app.
fun backendURL(): String {
val details = MutableStateFlow<TerminalDetails>(TerminalDetails.getDefaultInstance())
val job = CoroutineScope(Dispatchers.IO).launch {
repo.getTerminalDetails.collect {
details.value = it
}
}
runBlocking {
delay(250L)
}
return details.value.backendHost
}
EDIT 2: I fully fixed my issue. I created a method with the same name as my val (personal decision) which utilizes runBlocking{} and Flow<T>.first() to block while the value is retrieve. The reason I did not replace my val with the function is there are places where I need the information as well where I can utilize coroutines properly where I am not initializing components on my app
val getTerminalDetails: Flow<TerminalDetails> = cxt.terminalDetails.data
.catch { e ->
if (e is IOException) {
Log.d("Error", e.message.toString())
emit(TerminalDetails.getDefaultInstance())
} else {
throw e
}
}
fun getTerminalDetails(): TerminalDetails = runBlocking {
cxt.terminalDetails.data.first()
}
I am trying to make sure my app responds appropriate in the event of a backend failure, I am using realm/mongo to create an async task that fetches the user.
I have these two blocks:
override suspend fun logIn(accessToken: String) {
val user = logInInternal(accessToken)
realmAsyncOpen(user)
}
and
private suspend fun logInInternal(accessToken: String) = suspendCancellableCoroutine<User> { continuation ->
val customJWTCredentials: Credentials = Credentials.jwt(accessToken)
app.loginAsync(customJWTCredentials) {
if (it.isSuccess) {
continuation.resumeWith(Result.success(app.currentUser()!!))
} else {
continuation.resumeWithException(RealmLoginException().initCause(it.error))
}
}
}
logInInternal crashes when I hit the resumeWithException part. I have also tried using app.login(credentials) since the method is suspending, without luck there. Why does my app crash when I resume with exception?
I am causing the call to 502 out when hit.
The docs of resumeWithException say:
Resumes the execution of the corresponding coroutine so that the exception is re-thrown right after the last suspension point.
Which means you need to catch that exception:
override suspend fun logIn(accessToken: String) {
try {
val user = logInInternal(accessToken)
realmAsyncOpen(user)
} catch(e: RealmLoginException /*or e: Exception - to catch all exceptions*/) {
// handle exception
}
}
I need to implement a custom gRPC on Kotlin native side.
#ReactMethod can't be suspend func.
How can I run it?
#ReactMethod
fun connect(ipAddress: String, port: Int) {
try {
channel = ManagedChannelBuilder.forAddress(ipAddress, port).usePlaintext().build()
var guidKey = Metadata.Key.of("GUID", Metadata.ASCII_STRING_MARSHALLER)
metadata.put(guidKey, GUID)
val stub = DBServiceGrpcKt.DBServiceCoroutineStub(channel!!)
var request = GrpcDBService.SignInRequest.newBuilder()
.setUserName("user")
.setPassword("11111")
.build()
try {
//******* this part *****
suspend fun coroutine() {
var response = stub.trySignIn(request,metadata)
}
} catch (e: Exception) {
Log.d("grpcConnect", e.localizedMessage)
}
} catch (e: Error) {
Log.d("grpcConnect ", e.localizedMessage)
}
finally {
channel?.shutdown()
}
}
You need to create a coroutine, for example, define a scope (somewhere in your class) and use it with launch:
myPluginScope.launch {
val response = stub.trySignIn(request,metadata)
// Return, the result
}
Creating the scope is easy, the tricky part is to find where to cancel it. Check the documentation on React native modules to find a good place to call cancel on your scope:
val myPluginScope = CoroutineScope(SupervisorJob() + Dispatchers.Main.immediate)
Now, is important to decide whether the connect function should behave as an asynchronous function or not. For example, if the sign in operation takes time or uses the network, connect should probably return the result through a Promise or Callback, so the Javascript side is not blocked:
#ReactMethod
fun connect(ipAddress: String, port: Int, promise: Promise) {
myPluginScope.launch {
try {
// Make the sign in happen in a separate thread:
val response = withContext(context = Dispatchers.IO) {
stub.trySignIn(request, metadata)
}
// Resolve the promise in the calling thread (The UI thread)
promise.resolve(response.hypotheticalCode)
} catch (e: Exception) {
promise.reject("Sign in error!", e)
}
}
}
See:
https://reactnative.dev/docs/native-modules-android#promises
https://kotlinlang.org/docs/async-programming.html#coroutines
I have a suspend function
private suspend fun getResponse(record: String): HashMap<String, String> {}
When I call it in my main function I'm doing this, but the type of response is Job, not HashMap, how can I get the correct return type?
override fun handleRequest(event: SQSEvent?, context: Context?): Void? {
event?.records?.forEach {
try {
val response: Job = GlobalScope.launch {
getResponse(it.body)
}
} catch (ex: Exception) {
logger.error("error message")
}
}
return null
}
Given your answers in the comments, it looks like you're not looking for concurrency here. The best course of action would then be to just make getRequest() a regular function instead of a suspend one.
Assuming you can't change this, you need to call a suspend function from a regular one. To do so, you have several options depending on your use case:
block the current thread while you do your async stuff
make handleRequest a suspend function
make handleRequest take a CoroutineScope to start coroutines with some lifecycle controlled externally, but that means handleRequest will return immediately and the caller has to deal with the running coroutines (please don't use GlobalScope for this, it's a delicate API)
Option 2 and 3 are provided for completeness, but most likely in your context these won't work for you. So you have to block the current thread while handleRequest is running, and you can do that using runBlocking:
override fun handleRequest(event: SQSEvent?, context: Context?): Void? {
runBlocking {
// do your stuff
}
return null
}
Now what to do inside runBlocking depends on what you want to achieve.
if you want to process elements sequentially, simply call getResponse directly inside the loop:
override fun handleRequest(event: SQSEvent?, context: Context?): Void? {
runBlocking {
event?.records?.forEach {
try {
val response = getResponse(it.body)
// do something with the response
} catch (ex: Exception) {
logger.error("error message")
}
}
}
return null
}
If you want to process elements concurrently, but independently, you can use launch and put both getResponse() and the code using the response inside the launch:
override fun handleRequest(event: SQSEvent?, context: Context?): Void? {
runBlocking {
event?.records?.forEach {
launch { // coroutine scope provided by runBlocking
try {
val response = getResponse(it.body)
// do something with the response
} catch (ex: Exception) {
logger.error("error message")
}
}
}
}
return null
}
If you want to get the responses concurrently, but process all responses only when they're all done, you can use map + async:
override fun handleRequest(event: SQSEvent?, context: Context?): Void? {
runBlocking {
val responses = event?.records?.mapNotNull {
async { // coroutine scope provided by runBlocking
try {
getResponse(it.body)
} catch (ex: Exception) {
logger.error("error message")
null // if you want to still handle other responses
// you could also throw an exception otherwise
}
}
}.map { it.await() }
// do something with all responses
}
return null
}
You can use GlobalScope.async() instead of launch() - it returns Deferred, which is a future/promise object. You can then call await() on it to get a result of getResponse().
Just make sure not to do something like: async().await() - it wouldn't make any sense, because it would still run synchronously. If you need to run getResponse() on all event.records in parallel, then you can first go in loop and collect all deffered objects and then await on all of them.
I am trying to learn Kotlin coroutines recently I have noticed that in case of map that returns bunch of async IDE is displaying message saying that Function returning Deferred with a name that does not end with async. This is the code I have
runBlocking {
try {
val siteDeferred = async { getSite(order) }
// Place where I get warning-----------| (Function returning Deferred with a name that does not end with Async)
// v
val orderLineDeferred = order.line.map { async { getOrderDetail(it) } }
// Place where I get warning-------------------| (Function returning Deferred with a name that does not end with Async)
// v
val orderLineProductsDeferred = order.line.map { async { getOrderProductInformation(it.productId) } }
val site = siteDeferred.await()
val orderLine = orderLineDeferred.awaitAll()
val orderLineProducts = orderLineProductsDeferred.awaitAll()
} catch (e: Throwable) {
throw Exception(e.message)
}
}
private suspend getOrderDetail(OrderLine orderLine): OrderDetail...
private suspend getSite(Order order): Site ...
private suspend getOrderProductInformation(String productId): Product ...
Am I missing anything here. Furthermore, I would like to know whether this is the right way to do exception handling or not and is there a way to clean up try block so that I can get the value directly even if that means I will have to use async in other methods.
function getSite() renamed to getSiteAsync()，Others functions are modified in this way.