So, this is the problem :

My application calls a functionA in a third party library which creates its own thread and calls back the caller in that thread. What I want to do is call that functionA from a function in my app and wait until the callback has been called and then exit my function. I tried to use runBlocking, withContext etc., to no avail.

Below is a code snippet.

  fun appFunction(context: Context) {
    // call library function `functionA` which calls back the success and failure callbacks in a separate java thread.
    runBlocking {
      launch { functionA({ Timber.i("Call Success") }, { Timber.e(it) }) }
      joinAll()
    }
  }

I want the app function to return only after the callback method finishes executing. I was thinking using a launch would make all threads created inside the java library would be part of the same coroutine scope and joinAll() would wait on that. Obviously, I was wrong.

Is this something that could be achieved? If so, how?

Any help is appreciated.

CodePudding user response：

Try this https://stackoverflow.com/a/67599110/19645104 Save result of launch to job variable and wait it

CodePudding user response：

Standard way of doing this with coroutines is by using either suspendCoroutine() or suspendCancellableCoroutine(). They both suspend execution waiting to be resumed (for example from a callback) and the difference is that the latter additionally supports cancelling while waiting. I suggest reading docs for the cancellable variant, as docs are much better there.

Example with suspendCoroutine():

suspendCoroutine<Unit> { continuation ->
    functionA(
        { continuation.resume(Unit) },
        { continuation.resumeWithException(it) }
    )
}

Note that to use above, your function has to be a suspend function. In your question appFunction() is a regular function, so it can't suspend or wait for anything. Technically, you can use runBlocking(), but if you plan to block threads then I think it doesn't make too much sense to use coroutines - you can just use callbacks.