暂停Kotlin Coroutine不适用于凌空抽射

Question

I wrote following (test) function to talk to the google maps api via volley and with coroutines. Sadly it never finishes when calling it with the suspendCoroutine. If I use the same function, drop the coroutine stuff and implement a "normal" callback, everything works fine. I am kind of at a loss whats the problem here. Is anybody able to help?

Code executes until Log.d(LOGTAG, "AFTERAFTER"), but never reaches Log.d("findNaturalLocations", "Response: " + response)

suspend fun testNaturalLocations(tag: Tag, lastKnownUserLocation: 
Location): ArrayList<CLDistanceRequest> = suspendCoroutine { 
continuation ->

    Log.d("findNaturalLocations", "getDistanceAndTimeBetweenLocations")

    var distanceRequests = ArrayList<CLDistanceRequest>()

    val mapsBaseUrl = "https://maps.googleapis.com/maps/api/place/nearbysearch/"
    val mapsOutputFormat = "json"

    val location = "location=" + lastKnownUserLocation.latitude.toString() + "," + lastKnownUserLocation.longitude.toString()
    val radius = "radius=5000"
    val keyword = "keyword=Supermarket"
    val name = "name=Supermarket"
    val sensor = "sensor=true"
    val apiKey = "key=API_KEY"

    val finishedUrl = mapsBaseUrl + mapsOutputFormat + "?" + location + "&" + radius + "&" + keyword + "&" + name + "&" + sensor + "&" + apiKey

    Log.d(LOGTAG, finishedUrl)

    val jsObjectRequest = JsonObjectRequest(Request.Method.GET, finishedUrl, null,
            Response.Listener<JSONObject> { response ->
                Log.d("findNaturalLocations", "Response: " + response)

                var results = response.getJSONArray("results")

                // parse distanceRequests, ommitted for brevity

                continuation.resume(distanceRequests)
            },
            Response.ErrorListener { error ->
                Log.e("Error", error.localizedMessage, error)

                continuation.resumeWithException(error)
            }
    )

    Log.d(LOGTAG, "AFTER");

    jsObjectRequest.setShouldCache(false)
    CLGlobal.getRequestQueue().add(jsObjectRequest)

    Log.d(LOGTAG, "AFTERAFTER");
}

Doing the same with a simple callback works flawlessly.

var i = 0;
    runBlocking {
        val query = async(CommonPool) {
            i = this@CLTaskList.test2()
        }

        query.await()
    }

suspend fun test2():Int = suspendCoroutine<Int> { continuation ->
    Log.d("TESTTEST", "TEST2 CALLED")
    test {
        Log.d("TESTTEST", "CONTINUATION")
        continuation.resume(it)
    }
}

fun test(completionHandler: (Int) -> Unit) {
    Log.d("TESTTEST", "TEST CALLED")
    completionHandler(1)
}

Answer 1

As you reveal in your comment, this is how you run the query:

val query = async(CommonPool) { 
    this@CLTaskList.testNaturalLocations(tags[0], 
         CLGlobal.getInstance().mLastKnownLocation!!) 
} 
runBlocking<Unit> { query.await() }

You are close to getting it right, but this piece of code is all backwards:

1. You let the suspendable function run in a thread pool, relieving some worker thread of the duty to block until you get your answer (it wouldn't care if it's blocked);
2. You block your GUI thread with runBlocking .

In the correct solution you need none of async , CommonPool or runBlocking , all you need is this:

launch(UI) {
    val result = testNaturalLocations(tags[0], 
       CLGlobal.getInstance().mLastKnownLocation!!)
    // deal with the result right here
}

Since testNaturalLocations is a suspendable function, it's not blocking your UI thread, and when the callback you wrote resumes it, your code simply goes on to the next line, with result assigned.