``` cameraSource takePicture bytes gt detectFaces bytes fun

Question

``` cameraSource takePicture bytes gt detectFaces bytes fun detectFaces bytes ByteArray launch CommonPool val faces = facesClient detect bytes inputStream true false arrayOf FaceServiceClient FaceAttributeType Age val results = facesClient identity family faces map it faceId toTypedArray 4 results forEach r gt val name = personMap r candidates 0 personId toString Log i TAG Found $name ```

gildor · Answer

It s hard to follow not enough context First do not use CommonPool explicitly

gildor · Answer

It really depends what API that you use does and how works

gildor · Answer

Most probably you should just wrap blocking calls to own threads

Vinicius Carvalho · Answer

The client in question is from microsoft and uses just a regular blocking commons http connection under the hood

gildor · Answer

If this request is blocking wrap it to `withContext <http Dispatchers IO|Dispatchers IO> `

gildor · Answer

This will run this request on special IO dispatcher in a separate thread

Vinicius Carvalho · Answer

Is that 0 26 I m using 0 25

gildor · Answer

Yes 0 26

gildor · Answer

Use IO in 0 25

Vinicius Carvalho · Answer

gonna give it a try thank you

gildor · Answer

But I would migrate to 0 26 there are significant changes

gildor · Answer

Also this is bad style to hide launch in function that returns nothing

gildor · Answer

Instead use suspend function do not use launch

gildor · Answer

Use launch only on most top level of your program

Vinicius Carvalho · Answer

I kinda get it but don t a I need a context to run a suspend function Oh BTW this was a hack just to print the results I actually want the function to return the results

Vinicius Carvalho · Answer

I mean rewrite `suspend fun detectFaces bytes ByteArray `

Vinicius Carvalho · Answer

and then call it using `withContext <http Dispatchers IO|Dispatchers IO> detectFaces ` is that what you are saying

gildor · Answer

No I m talking about something like that ```suspend fun detectFaces SomeResult = withContext IO Some blocking code that returns SomeResult ```

gildor · Answer

And than call it from any coroutine with any context for example UI without problems and boilerplate

Vinicius Carvalho · Answer

Still not working I think it has to do on how my function gets called

Vinicius Carvalho · Answer

so I have a CameraSource that has a Detector and a `Tracker` it seems that the source can create as many Tracker instances as it wants I first thought the Tracker to be a single instance per CameraSource

Vinicius Carvalho · Answer

so on the Tracker method I call cameraSource takePicture callback

Vinicius Carvalho · Answer

seems that the Tracker reference gets destroyed before the connection and the suspended function ends

Vinicius Carvalho · Answer

I tried to move all to the Main Activity but still the same problem happens Even after declaring the suspended function and the callback as a top level lambda

Vinicius Carvalho · Answer

```val cameraCallback ByteArray gt Unit = bytes gt GlobalScope launch <http Dispatchers IO|Dispatchers IO> val results = detectFaces bytes results forEach Log i TAG Person $ personMap it candidates 0 personId toString ```

gildor · Answer

What is exactly doesn t work Your original problem was with NetworkOnMainThread

Vinicius Carvalho · Answer

No I said that following that pattern I m no longer gettting an NetworkOnMainError Which I really ain t

Vinicius Carvalho · Answer

I m positive that it has to be due some object being reclaimed by the GC and the context that holds the thread that was running being destroyed before it finishes

Vinicius Carvalho · Answer

but it s not easy to find out

Vinicius Carvalho · Answer

I simplified my code to run outside of the main activity that was too long

gildor · Answer

gt seems that the Tracker reference gets destroyed before the connection and the suspended function ends Sure because you have callback so coroutine is destroyd

Vinicius Carvalho · Answer

and the code now works fine using the library

gildor · Answer

Maybe you should just write callback to coroutines adapter for this method

gildor · Answer

so it will be much easier to use you just call method and suspend until event

gildor · Answer

It s hard to recommend something without knowing context and understanding real problem

gildor · Answer

gt I m positive that it has to be due some object being reclaimed by the GC and the context that holds the thread that was running being destroyed before it finishes If you keep reference on this object GC cannot collect it

Vinicius Carvalho · Answer

Context I m detecting faces on a cameraSource stream I just got the code from the google vision samples

gildor · Answer

I understand but need some code to understand what is wrong Nothing magic how coroutines work with such code You should have very similar code without coroutines Coroutine just allow to easily wrap to background thread and use coroutine syntax for callbacks

Vinicius Carvalho · Answer

I think the first real problem is that the Detector class creates many instances of a class `Tracker` that is the class with the method that has an event when a face is found

gildor · Answer

Yeah but it doesn t look related to coroutines not sure how this API should work

Vinicius Carvalho · Answer

Sure I don t think it s coroutines either its just a mismatch on how to adapt this code with coroutines I ll give the adapter a try done that before never used coroutines with android only on ktor

gildor · Answer

If you have working code without coroutines I can try to help it also can help you to understand what is going on there and where is problem Otherwise not sure what exactly problem with adapting code with coroutines

Vinicius Carvalho · Answer

I don t have a version without coroutines I was hoping to solve the background thread issue with it I ll try to get something done with plain threads just for the sake of getting it working and I ll update the thread anyway thank you

gildor · Answer

I don t think that this is problem of threads

gildor · Answer

You can wrap to coroutines just like to threads

gildor · Answer

I just thought that you know how this API works

Vinicius Carvalho · Answer

Wouldn t make much sense asking for help if I did right wink

gildor · Answer

Haa sweat smile