Hi! I am trying to do http requests in Kotlin Native in ios jsing nsurlsession. I want to do it sync...

# kotlin-native

[Mohit Gurumukhani]

Hi! I am trying to do http requests in Kotlin Native in ios jsing nsurlsession. I want to do it synchronously and so am using semaphores. However, when the callback for dataTaskWithRequest ends, I get a bad access error which according to the debugger, is caused due to garbage collection. Even when I comment out the first three lines of the callback lambda, I keep getting the error. Any help would be appreciated.

fun call() : Unit{

    var url = NSURL.alloc()
    url = url?.initWithString("<https://jsonplaceholder.typicode.com/posts/1>")
    var nsrequest = NSMutableURLRequest(url as NSURL)

    nsrequest.HTTPMethod = "GET"

    var this_nsdata : NSData? = null
    var this_nsresponse : NSURLResponse? = null
    var this_nserror : NSError? = null
    var syncer = dispatch_semaphore_create(0)

    var sess = NSURLSession.sharedSession()

    var task = sess.dataTaskWithRequest(nsrequest) { nsdata: NSData?, nsresponse: NSURLResponse?, nserror: NSError? ->
        this_nsdata = nsdata
        this_nsresponse = nsresponse as NSHTTPURLResponse
        this_nserror = nserror


        dispatch_semaphore_signal(syncer)
    }

    task.resume()

    dispatch_semaphore_wait(syncer, DISPATCH_TIME_FOREVER)

    if(this_nserror == null && this_nsdata != null){

        this_nsresponse as NSHTTPURLResponse
        var nsstrobj = NSString.stringWithUTF8String(this_nsdata!!.bytes as CPointer<ByteVar>)
        print(nsstrobj as String)
    }
    else {
        print("whoops")

    }
}

[olonho]

I would suggest to use common HTTP client as in https://github.com/e5l/http-client-common/tree/master/samples/ios-test-application, also looking at https://github.com/JetBrains/kotlin-native/blob/7e517ef6f1154a59473dd6b8a4c3dd39fe5c1360/samples/objc/src/main/kotlin/Window.kt#L39 may give you some insight how one could do general async ops

[thevery]

You need AtomicReference for cross-thread calls

[thevery]

+initRuntimeIfNeeded()

[spierce7]

is initRuntimeIfNeeded() ever going to go away and be handled by the compiler?

[spierce7]

@thevery Why does the AtomicReference need to be used? If the write access is definitively atomic from the semaphore, is the AtomicReference necessary?

[thevery]

iOS semaphore is not the same as java semaphore - you don't have memory model guarantees in KN

[thevery]

{ nsdata: NSData?, nsresponse: NSURLResponse?, nserror: NSError? -> lambda is invoked in bg thread -> thread crossing triggers immutability violation

[thevery]

@spierce7 see https://github.com/JetBrains/kotlin-native/issues/1279 and https://github.com/JetBrains/kotlin-native/blob/master/IMMUTABILITY.md

[thevery]

As for initRuntimeIfNeeded, @olonho should know better than me 😃

[thevery]

And for string conversion use val body = data?.let { NSString.create(it, NSUTF8StringEncoding) as? String } ?: ""

[olonho]

initRuntimeIfNeeded will go away eventually