Hello, we have a gps location service that we cre...

# coroutines

[Paulius Ruminas]

Hello,

we have a gps location service that we create using dagger and we are getting an exception that _location channel was closed and we are not sure how can this happen since _location is a private member and there is no call to _location.close(). What are we missing?

Dagger

@Provides
    @Singleton
    fun gpsLocationService(): GpsLocationService = GpsLocationService(
        context = context,
        coroutineContext = Dispatchers.Default
    )

Service

class GpsLocationService(
    private val context: Context,
    override val coroutineContext: CoroutineContext
) : CoroutineScope {

    private val logger = Logger.get(this::class)

    private val _location = BroadcastChannel<Location>(1)

    private val interval: Millis = GpsUpdateInterval.High.interval

    private val fusedLocationClient = LocationServices.getFusedLocationProviderClient(context)

    private val locationCallback: LocationCallback = object : LocationCallback() {
        override fun onLocationResult(locationResult: LocationResult) {
            if (GpsHelper.isGpsEnabled(context)) {
                logger.trace("Location acquired (${locationResult.lastLocation}).")
                _location.sendBlocking(locationResult.lastLocation)
            } else {
                logger.trace("GPS is disabled, ignoring location change.")
            }
        }
    }

    suspend fun requestLocation(): Location? = _location.openSubscription().consume {
        val location = withTimeoutOrNull(15.seconds) { receiveOrNull() }

        location
    }
}

[bohsen]

Using _location.openSubscription().consume {} will invoke cancel() after consuming. You should use consumeEach instead.

[bohsen]

Docs: https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.channels/consume.html

[bohsen]

You should consider changing requestLocation() to return Flow<Location>

[bohsen]

BroadcastChannel has an asFlow extension AFAIK

[Paulius Ruminas]

I need one value and that's why I use consume (consumeEach uses consume as well just uses a loop to retrieve next values). Consume does not close the broadcast channel

@Test
    fun test() {
        val a = BroadcastChannel<Unit>(1)

        runBlocking {
            a.openSubscription().consume {

            }
        }

        kotlin.test.assertEquals(a.isClosedForSend, false)
    }

[bohsen]

But why then use a BroadcastChannel?

[Paulius Ruminas]

fun requestUpdates(): ReceiveChannel<Location> = _location.openSubscription()

I have this method in the class as well just did not copy it into the example.

[Paulius Ruminas]

@elizarov are there any other ways besides .close() that a broadcast channel could be closed? I can not figure that out from the stack trace since there is no information about who closed the channel.

Fatal Exception: kotlinx.coroutines.channels.ClosedSendChannelException: Channel was closed
       at kotlinx.coroutines.channels.Closed.getSendException(AbstractChannel.kt:1048)
       at kotlinx.coroutines.channels.AbstractSendChannel.offer(AbstractChannel.kt:166)
       at kotlinx.coroutines.channels.AbstractSendChannel.send(AbstractChannel.kt:146)
       at kotlinx.coroutines.channels.BroadcastCoroutine.send$suspendImpl(Broadcast.kt)
       at kotlinx.coroutines.channels.BroadcastCoroutine.send(Broadcast.kt)
       at kotlinx.coroutines.channels.BroadcastKt$broadcast$1.invokeSuspend(Broadcast.kt:30)
       at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
       at kotlinx.coroutines.ResumeModeKt.resumeMode(ResumeMode.kt:67)
       at kotlinx.coroutines.DispatchedKt.resume(Dispatched.kt:319)
       at kotlinx.coroutines.DispatchedKt.resumeUnconfined(Dispatched.kt:49)
       at kotlinx.coroutines.DispatchedKt.dispatch(Dispatched.kt:298)
       at kotlinx.coroutines.CancellableContinuationImpl.dispatchResume(CancellableContinuationImpl.kt:250)
       at kotlinx.coroutines.CancellableContinuationImpl.completeResume(CancellableContinuationImpl.kt:327)
       at kotlinx.coroutines.channels.AbstractChannel$ReceiveHasNext.completeResumeReceive(AbstractChannel.kt:907)
       at kotlinx.coroutines.channels.ArrayBroadcastChannel$Subscriber.checkOffer(ArrayBroadcastChannel.kt:256)
       at kotlinx.coroutines.channels.ArrayBroadcastChannel.checkSubOffers(ArrayBroadcastChannel.kt:127)
       at kotlinx.coroutines.channels.ArrayBroadcastChannel.offerInternal(ArrayBroadcastChannel.kt:96)
       at kotlinx.coroutines.channels.AbstractSendChannel.offer(AbstractChannel.kt:160)
       at kotlinx.coroutines.channels.AbstractSendChannel.send(AbstractChannel.kt:146)
       at com.eld.android.gps.GpsLocationService$locationCallback$1$onLocationResult$1.invokeSuspend(GpsLocationService.kt:34)
       at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
       at kotlinx.coroutines.DispatchedTask.run(Dispatched.kt:241)
       at kotlinx.coroutines.EventLoopImplBase.processNextEvent(EventLoop.common.kt:270)
       at kotlinx.coroutines.BlockingCoroutine.joinBlocking(Builders.kt:79)
       at kotlinx.coroutines.BuildersKt__BuildersKt.runBlocking(Builders.kt:54)
       at kotlinx.coroutines.BuildersKt.runBlocking(:1)
       at kotlinx.coroutines.BuildersKt__BuildersKt.runBlocking$default(Builders.kt:36)
       at kotlinx.coroutines.BuildersKt.runBlocking$default(:1)
       at com.eld.android.gps.GpsLocationService$locationCallback$1.onLocationResult(GpsLocationService.kt:34)
       at com.google.android.gms.internal.location.zzau.notifyListener()
       at com.google.android.gms.common.api.internal.ListenerHolder.notifyListenerInternal(:17)
       at com.google.android.gms.common.api.internal.ListenerHolder$zaa.handleMessage(:5)
       at android.os.Handler.dispatchMessage(Handler.java:111)
       at com.google.android.gms.internal.base.zap.dispatchMessage(:8)
       at android.os.Looper.loop(Looper.java:207)
       at android.os.HandlerThread.run(HandlerThread.java:61)

[bohsen]

Its caused by consume. Just sayin'.
Check docs on consume and cancel. You probably call requestLocation() somewhere before you invoke your locationCallback.

[Paulius Ruminas]

Then why does my given test case not close the broadcast channel?