Concurrency problem with Coroutines and Socket Android - android

I have a chat application which of course works with Sockets. So i have build a SocketManager where i have the callbacks and the sendMethod from the implementation 'com.neovisionaries:nv-websocket-client:2.14' library
override fun sendMessage(text: String) {
println("## SEND: $text")
webSocket?.let {
it.sendText(text)
}
}
override fun onTextMessage(websocket: WebSocket?, message: String?) {
super.onTextMessage(websocket, message)
println("## RECEIVED: Something received")
try {
flowSocketHandler.webSocketEventResolver(s, message) {
sendMessage(it)
}
} catch (e: Exception) {
e.printStackTrace()
}
}
When a new text comes from Socket the FlowSocketHandler resolves the type of message and calls the proper handler to handle the message. For example, FileHandler for File messages, MEssageHandler for simple messages, VideoHandler for video call messages.
private val scope = CoroutineScope(Dispatchers.Main + SupervisorJob())
override fun webSocketEventResolver(server: Server, message: String, socketCallback: (message: String) -> Unit) {
scope.launch(Dispatchers.IO) {
try {
val json = JSONObject(message)
when(Enums.SocketResponses.toSocketEvent(json)) {
Enums.SocketResponses.MESSAGE_RECEIVED -> messagesHandler.onMessageReceived(server, json.fromJson(), true, socketCallback)
Enums.SocketResponses.FILE_PART_RECEIVED -> filesHandler.onFilePartReceived(server, json.fromJson(), socketCallback)
else -> {}
}
} catch (e: Exception) {
e.printStackTrace()
}
}
}
Also, the philopsophy of downloading an incoming File message, is that
I have an incoming Text message that says "Hey, you have to download a file that consists of 1000 parts" which calls the MESSAGE_RECEIVED
I send 1000 socket messages requesting each part accordingly
I receive each part from Socket and handle it which calls the FILE_PART_RECEIVED
As you can see above, all this is taking place in a scope CoroutineScope
All this is taking place inside the FilesHandler
class FilesHandlerImpl(private val appContext: Context): FilesHandler, KoinComponent {
private val scope = CoroutineScope(Dispatchers.Main + SupervisorJob())
override suspend fun onFileHeaderReceived(
server: Server,
receiver: ReceiveNewMessage,
isFromSocket: Boolean,
socketCallback: ((message: String) -> Unit)?
) {
scope.launch(Dispatchers.IO) {
// Do some checks and start send requests for each part
println("## Time header message ${receiver.fileHash}")
pendingList.forEach { p ->
socketCallback?.invoke(requestFilePart(p))
}
// So here in the Log i see
// ## Send {json for each part}
}
}
// Take the part and create a file
override suspend fun onFilePartReceived(
server: Server,
receiver: FilePartRcv,
socketCallback: (message: String) -> Unit
) {
scope.launch(Dispatchers.IO) {
println("## File part received ${receiver.filePart.segment}")
filesRepository.createAndWriteFilePart(server, receiver)
filesRepository.updateFilePartStatus(server, receiver, FILE_PART_RECEIVED)
if (complete) {
// Do stuff
}
}
// So here in every part we receive we see in the Log
// ## File part received 1
// ## File part received 4
// ## File part received 2
// ## File part received 6
// ## File part received 9
......
}
}
The problem is the Following.
While the client sends requests for the File parts (So Log is full of ## SEND {...}) meanwhile the Socket callback onTextMessage is called so i see also ## RECEIVED: Something received.
Those callbacks are the incoming File Parts. So i should also see the ## File part received X. But i don't see any of those UNTIL the Send loop finishes. Then suddenly i see all the ## File part received X.
What i did, is to remove the scope from onFileHeaderReceived and onFilePartReceived and seems to play a bit smoother.
Can anybody explain me why is that happening?

scope.launch starts a job asynchronously. it returns a Job that you can hold onto and cancel on await.
If you just want to ensure the job happens on the IO Dispatcher, then you probably want withContext instead. This will be blocking so operations will happen sequentially.
withContext(Dispatchers.IO) {
...
}
Dispatchers.Main will typically be single threaded also, so forming a queue as you suggest. You could use Dispatchers.IO or Default to have concurrency.
https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/-dispatchers/-main.html
A coroutine dispatcher that is confined to the Main thread operating with UI objects. Usually such dispatchers are single-threaded.
Also suspend isn't needed is it just calls scope.launch, since that isn't a suspending function.

Related

Kotlin coroutine does not run synchronously

In all cases that I have been using corrutines, so far, it has been executing its "lines" synchronously, so that I have been able to use the result of a variable in the next line of code.
I have the ImageRepository class that calls the server, gets a list of images, and once obtained, creates a json with the images and related information.
class ImageRepository {
val API_IMAGES = "https://api.MY_API_IMAGES"
suspend fun fetch (activity: AppCompatActivity) {
activity.lifecycleScope.launch() {
val imagesResponse = withContext(Dispatchers.IO) {
getRequest(API_IMAGES)
}
if (imagesResponse != null) {
val jsonWithImagesAndInfo = composeJsonWithImagesAndInfo(imagesResponse)
} else {
// TODO Warning to user
Log.e(TAG, "Error: Get request returned no response")
}
...// All the rest of code
}
}
}
Well, the suspend function executes correctly synchronously, it first makes the call to the server in the getRequest and, when there is response, then composes the JSON. So far, so good.
And this is the call to the "ImageRepository" suspension function from my main activity:
lifecycleScope.launch {
val result = withContext(Dispatchers.IO) { neoRepository.fetch(this#MainActivity) }
Log.i(TAG, "After suspend fun")
}
The problem is that, as soon as it is executed, it calls the suspension function and then displays the log, obviously empty. It doesn't wait for the suspension function to finish and then display the log.
Why? What am I doing wrong?
I have tried the different Dispatchers, etc, but without success.
I appreciate any help.
Thanks and best regards.
It’s because you are launching another coroutine in parallel from inside your suspend function. Instead of launching another coroutine there, call the contents of that launch directly in your suspend function.
A suspend function is just like a regular function, it executes one instruction after another. The only difference is that it can be suspended, meaning the runtime environment can decide to halt / suspend execution to do other work and then resume execution later.
This is true unless you start an asynchronous operation which you should not be doing. Your fetch operation should look like:
class ImageRepository {
suspend fun fetch () {
val imagesResponse = getRequest(API_IMAGES)
if (imagesResponse != null) {
val jsonWithImagesAndInfo = composeJsonWithImagesAndInfo(imagesResponse)
} else {
// TODO Warning to user
Log.e(TAG, "Error: Get request returned no response")
}
... // All the rest of code
}
}
-> just like a regular function. Of course you need to all it from a coroutine:
lifecycleScope.launch {
val result = withContext(Dispatchers.IO) { neoRepository.fetch() }
Log.i(TAG, "After suspend fun")
}
Google recommends to inject the dispatcher into the lower level classes (https://developer.android.com/kotlin/coroutines/coroutines-best-practices) so ideally you'd do:
val neoRepository = ImageRepository(Dispatchers.IO)
lifecycleScope.launch {
val result = neoRepository.fetch()
Log.i(TAG, "After suspend fun")
}
class ImageRepository(private val dispatcher: Dispatcher) {
suspend fun fetch () = withContext(dispatcher) {
val imagesResponse = getRequest(API_IMAGES)
if (imagesResponse != null) {
val jsonWithImagesAndInfo = composeJsonWithImagesAndInfo(imagesResponse)
} else {
// TODO Warning to user
Log.e(TAG, "Error: Get request returned no response")
}
... // All the rest of code
}
}

Android Kotlin Coroutine Channel message not sended in websocket callback

I am developing an chat android app using WebSocket (OkHttp)
To do this, I implemented the okhttp3.WebSocketListener interface.
And I am receiving the chat messages from the onMessage callback method.
I already developed it using the Rx-PublishSubject, and it works fine.
But I want to change it to Coroutine-Channel.
To do this, I added the Channel in my WebSocketListener class.
#Singleton
class MyWebSocketService #Inject constructor(
private val ioDispatcher: CoroutineDispatcher
): WebSocketListener() {
// previous
val messageSubject: PublishSubject<WsMsg> = PublishSubject.create()
// new
val messageChannel: Channel<WsMsg> by lazy { Channel() }
override fun onMessage(webSocket: WebSocket, text: String) {
super.onMessage(webSocket, text)
// previous
messageSubject.onNext(text)
// new
runBlocking(ioDispatcher) {
Log.d(TAG, "message: $text")
messageChannel.send(text)
}
}
}
But... the coroutine channel doesn't work...
It receives and prints the Log only once.
But it doesn't print the log after the second message.
But when I change the code like below, it works!
override fun onMessage(webSocket: WebSocket, text: String) {
super.onMessage(webSocket, text)
GlobalScope.launch(ioDispatcher) {
Log.d(TAG, "message: $text")
messageChannel.send(text)
}
}
The difference is runBlocking vs GlobalScope.
I head that the GlobakScope may not ensure the message's ordering.
So It is not suitable for the Chat app.
How can I solve this issue?
The default Channel() has no buffer, which causes send(message) to suspend until a consumer of the channel calls channel.receive() (which is implicitely done in a for(element in channel){} loop)
Since you are using runBlocking, suspending effectively means blocking the current thread. It appears that okhttp will always deliver messages on the same thread, but it can not do that because you are still blocking that thread.
The correct solution to this would be to add a buffer to your channel. If it is unlikely that messages will pour in faster than you can process them, you can simply replace Channel() with Channel(Channel.UNLIMITED)

Android WorkManager - Can I pass input data to a Worker that runs periodically?

In my app I start a WebSocketWorker tasks that runs periodically every 15 minutes. As the name implies, it contains a WebSocket for listening to a socket in the background:
// MainApplication.kt
override fun onCreate() {
super.onCreate()
if (BuildConfig.DEBUG) {
Timber.plant(DebugTree())
}
val work = PeriodicWorkRequestBuilder<WebSocketWorker>(15, TimeUnit.MINUTES).build()
workManager.enqueueUniquePeriodicWork("UniqueWebSocketWorker", ExistingPeriodicWorkPolicy.KEEP, work)
}
The WebSocketWorker contains the following logic:
#HiltWorker
class WebSocketWorker #AssistedInject constructor(
#Assisted appContext: Context,
#Assisted workerParams: WorkerParameters
) : CoroutineWorker(appContext, workerParams) {
inner class MyWebSocketListener : WebSocketListener() {
override fun onMessage(webSocket: WebSocket, text: String) {
Timber.d("The message sent is %s", text)
// do sth. with the message
}
override fun onFailure(webSocket: WebSocket, t: Throwable, response: Response?) {
t.localizedMessage?.let { Timber.e("onFailure: %s", it) }
response?.message?.let { Timber.e("onFailure: %s", it) }
}
}
override suspend fun doWork(): Result {
try{
// code to be executed
val request = Request.Builder().url("ws://***.***.**.***:8000/ws/chat/lobby/").build()
val myWebSocketListener = MyWebSocketListener()
val client = OkHttpClient()
client.newWebSocket(request, myWebSocketListener)
return Result.success()
}
catch (throwable:Throwable){
Timber.e("There is a failure")
Timber.e("throwable.localizedMessage: %s", throwable.localizedMessage)
// clean up and log
return Result.failure()
}
}
}
As you can see, in the Worker class I set the WebSocket and everything is fine. Listening to the socket works.
Now, I also want to add the "sending of messages" functionality to my app. How can I reuse the websocket created in WebSocketWorker? Can I pass input data to the WebSocketWorker that runs in the background ?
Let's say I have a EditText for typing the message and a Button to send the message with a setOnClickListener attached like this:
binding.sendButton.setOnClickListener {
// get message
val message = binding.chatMessageEditText.text.toString()
// check if not empty
if(message.isNotEmpty()) {
// HOW CAN I REUSE THE WEBSOCKET RUNNING PERIODICALLY IN THE BACKGROUND?
// CAN I PASS THE MESSAGE TO THAT WEBSOCKET ?
// OR SHOULD I CREATE A DIFFERENT WORKER FOR SENDING MESSAGES (e.g.: a OneTimeRequest<SendMessageWorker> for sending messages ?
}
}
From the documentation, I know that you need to build Data objects for passing inputs and so on but there was no example which showcased how to pass input to a worker running periodically in the background.
My experience is saying that you can. Basically you "can't" interact with the worker object via the API. It is really annoying.
For example, with the JS you have the option to get a job and check the parameters of the job. There is no such option with the work. For example, I want to check what is the current state of the restrictions - what is satisfied, what is not. Nothing like this. You can just check states, cancel and that is almost all.
My suggestions is that it is because the WorkManager is a "facade/adapter" over other libraries like JS. It has it's own DB to restore JS jobs on device restart and stuff like this, but beside that if you want to interact with the internals I guess it was just too complicated for them to do so they just skipped.
You can just inject some other object and every time the work can ask it for it's data. I don't see other option.

How to make request calls to remote service one by one usnig rx and kotlin?

I have remote service to which the app have to send data:
Definition in retrofit2:
interface FooRemoteService {
#POST("/foos")
fun postFoos(#Body foos: List<FooPojo>): Observable<Response<List<String>>
}
but the call has a limits no more than X Foos at once.
Each call can returns 206 code "partially successful" with list of unsuccessful uploaded foos. Also 413 "Request Entity Too Large". And of course 400 and 500 as well.
And the app needs to send unknown count of foo items (defined by user in runtime).
To avoid DDoS of service app is required to send this calls one by one.
So I made such implementation in my FooRepositoryImpl:
This is an idea. I'm not happy with below solution and I'm sure that it can be done much better but I'm run out of ideas. So any proposes?
override fun postFoos(foos: List<Foo>) Completable {
val fooChunks = divideListInToChuncksUnderRequestLimit(foos)
val unuploadedFoos = mutableListOf<UnuploadedFoo>()
fooChunks.fold(unuploadedFoos)
{ accu: MutableList<UnuploadedFoo>, chunk ->
fooRemoteService
.postFoos(chunk)
.subscribeOn(Schedulers.io())
.flatMapCompletable {
if (it.isSuccessful) {
Completable.complete()
} else {
Timber.e("$it")
accu.add(it.body())
}
}.blockingAwait()
responses
}
return Completable.complete()
}
At the end the app should display list of all unsuccessful foos or if any available. So I need pass from that fuction list of unuploaded Foos.
If you are OK with modifying the return type of postFoos a bit, something like this could work:
override fun postFoos(foos: List<Foo>): Observable<List<UnuploadedFoo>> {
val chunks = foos.chunked(CHUNK_SIZE)
val posters = chunks.map { chunk ->
fooRemoteService.postFoos(chunk)
.map { response ->
response.unUploaded.takeIf { !response.isSuccessful } ?: emptyList()
}
.filter { it.isNotEmpty() }
.toObservable()
}
return Observable.concatDelayError(posters)
}
I'm imagining your service to have something like:
data class Response(val isSuccessful: Boolean, val unUploaded: List<UnoploadedFoo>)
fun postFoos(foos: List<Foo>): Single<Response>
The trick here is that Concat:
(...) waits to subscribe to each additional Observable that you pass to it until the previous Observable completes.

Kotlin Coroutine to escape callback hell

I'm trying to use Kotlin's coroutines to avoid callback hell, but it doesnt look like I can in this specific situation, I would like some thougths about it.
I have this SyncService class which calls series of different methods to send data to the server like the following:
SyncService calls Sync Student, which calls Student Repository, which calls DataSource that makes a server request sending the data through Apollo's Graphql Client.
The same pattern follows in each of my features:
SyncService -> Sync Feature -> Feature Repository -> DataSource
So every one of the method that I call has this signature:
fun save(onSuccess: ()-> Unit, onError:()->Unit) {
//To Stuff here
}
The problem is:
When I sync and successfully save the Student on server, I need to sync his enrollment, and if I successfully save the enrollment, I need to sync another object and so on.
It all depends on each other and I need to do it sequentially, that's why I was using callbacks.
But as you can imagine, the code result is not very friendly, and me and my team starting searching for alternatives to keep it better. And we ended up with this extension function:
suspend fun <T> ApolloCall<T>.execute() = suspendCoroutine<Response<T>> { cont ->
enqueue(object: ApolloCall.Callback<T>() {
override fun onResponse(response: Response<T>) {
cont.resume(response)
}
override fun onFailure(e: ApolloException) {
cont.resumeWithException(e)
}
})
}
But the function in DataSource still has a onSuccess() and onError() as callbacks that needs to be passed to whoever call it.
fun saveStudents(
students: List<StudentInput>,
onSuccess: () -> Unit,
onError: (errorMessage: String) -> Unit) {
runBlocking {
try {
val response = GraphQLClient.apolloInstance
.mutate(CreateStudentsMutation
.builder()
.students(students)
.build())
.execute()
if (!response.hasErrors())
onSuccess()
else
onError("Response has errors!")
} catch (e: ApolloException) {
e.printStackTrace()
onError("Server error occurred!")
}
}
}
The SyncService class code changed to be like:
private fun runSync(onComplete: () -> Unit) = async(CommonPool) {
val syncStudentProcess = async(coroutineContext, start = CoroutineStart.LAZY) {
syncStudents()
}
val syncEnrollmentProcess = async(coroutineContext, start = CoroutineStart.LAZY) {
syncEnrollments()
}
syncStudentProcess.await()
syncEnrollmentProcess.await()
onComplete()
}
It does execute it sequentially, but I need a way to stop every other coroutine if any got any errors. Error that might come only from Apollo's
So I've been trying a lot to find a way to simplify this code, but didn't get any good result. I don't even know if this chaining of callbacks can be simplify at all. That's why I came here to see some thoughts on it.
TLDR: I want a way to execute all of my functions sequentially, and still be able to stop all coroutines if any got an exception without a lot o chaining callbacks.

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