Kotlin/Native - illegal attempt to access non-shared <object>

Question

In my app, I have two classes, a swift class inheriting from a kotlin class:

Swift class:

public class MySensor: RawSensor

    [...]

    public override func notifyChanged(values: KotlinFloatArray) {
      super.notifyChanged(values: values)
    }
}

Kotlin class:

package com.mycompany.myapp.mypackage.sensors.rawsensors

import com.mycompany.myapp.mypackage.util.Observable

abstract class RawSensor : Observable() {

  protected abstract val sensorDataType: RawSensorData.SensorDataType

  abstract val currentTime: Long

  protected open fun notifyChanged(values: FloatArray) {
      notifyObservers(RawSensorData(values, sensorDataType, currentTime))
  }

  abstract fun start()

  abstract fun stop()
}

When super.notifyChanged(values: values) is called, the app crashes with the following error:

Uncaught Kotlin exception: kotlin.native.IncorrectDereferenceException: illegal attempt to access non-shared <object>@83cb47c8 from other thread
Uncaught Kotlin exception: kotlin.native.IncorrectDereferenceException: illegal attempt to access non-shared <object>@83cb4788 from other thread
        at 0   MyNativeFramework                   0x00000001048815dc kfun:kotlin.Exception.<init>(kotlin.String?)kotlin.Exception + 84
        at 1   MyNativeFramework                   0x00000001048805f8 kfun:kotlin.RuntimeException.<init>(kotlin.String?)kotlin.RuntimeException + 84
        at 2   MyNativeFramework                   0x00000001048ac630 kfun:kotlin.native.IncorrectDereferenceException.<init>(kotlin.String)kotlin.native.IncorrectDereferenceException + 84
        at 3   MyNativeFramework                   0x00000001048ad7bc ThrowIllegalObjectSharingException + 496
        at 4   MyNativeFramework                   0x0000000104a6f1a0 _ZNK16KRefSharedHolder3refEv + 240
        at 5   MyNativeFramework                   0x0000000104a6eeb0 -[KotlinBase retain] + 52
        at 6   libobjc.A.dylib                     0x00000001aad36288 objc_retain + 88
        at 7   PositionKit                         0x000000010449454c $s11PositionKit21MySensorC13notifyChanged6valuesySo19MyNativeLibraryKotlinFloatArrayC_tFTo + 56
        at 8   PositionKit                         0x0000000104493fa0 $s11PositionKit21MySensorC5startyyFySo19CMAccelerometerDataCSg_s5Error_pSgtcfU_ + 796
        at 9   PositionKit                         0x00000001044941ec $sSo19CMAccelerometerDataCSgs5Error_pSgIeggg_ACSo7NSErrorCSgIeyByy_TR + 152
        at 10  CoreMotion                          0x00000001b7c44a8c CLClientCreateIso6709Notation + 30848
        at 11  Foundation                          0x00000001ab3d1c60 672CF0CB-4951-3B91-89DF-55E953AEA00F + 1170528
        at 12  Foundation                          0x00000001ab2d37e8 672CF0CB-4951-3B91-89DF-55E953AEA00F + 129000
        at 13  Foundation                          0x00000001ab3d3fbc 672CF0CB-4951-3B91-89DF-55E953AEA00F + 1179580
        at 14  Foundation                          0x00000001ab2d3464 672CF0CB-4951-3B91-89DF-55E953AEA00F + 128100
        at 15  Foundation                          0x00000001ab3d49e8 672CF0CB-4951-3B91-89DF-55E953AEA00F + 1182184
        at 16  Foundation                          0x00000001ab3d44a8 672CF0CB-4951-3B91-89DF-55E953AEA00F + 1180840
        at 17  libdispatch.dylib                   0x0000000104f59a48 _dispatch_block_async_invoke2 + 144
        at 18  libdispatch.dylib                   0x0000000104f4b2a8 _dispatch_client_callout + 20
        at 19  libdispatch.dylib                   0x0000000104f5935c _dispatch_main_queue_callback_4CF + 1376
        at 20  CoreFoundation                      0x00000001aaf7ce20 97285ACB-7B21-393A-ABF6-03F1DBB5D2A2 + 712224
        at 21  CoreFoundation                      0x00000001aaf77b7c 97285ACB-7B21-393A-ABF6-03F1DBB5D2A2 + 691068
        at 22  CoreFoundation                      0x00000001aaf77098 CFRunLoopRunSpecific + 480
        at 23  GraphicsServices                    0x00000001b50e1534 GSEventRunModal + 108
        at 24  UIKitCore                           0x00000001af0977ac UIApplicationMain + 1940
        at 25  MyTestApp                           0x00000001044383a4 main + 76
        at 26  libdyld.dylib                       0x00000001aadf6f30 0DC9A4BA-C3E8-3487-99DB-1B5C86597AF5 + 3888
        at 0   MyNativeFramework                   0x00000001048815dc kfun:kotlin.Exception.<init>(kotlin.String?)kotlin.Exception + 84
        at 1   MyNativeFramework                   0x00000001048805f8 kfun:kotlin.RuntimeException.<init>(kotlin.String?)kotlin.RuntimeException + 84
        at 2   MyNativeFramework                   0x00000001048ac630 kfun:kotlin.native.IncorrectDereferenceException.<init>(kotlin.String)kotlin.native.IncorrectDereferenceException + 84
        at 3   MyNativeFramework                   0x00000001048ad7bc ThrowIllegalObjectSharingException + 496
        at 4   MyNativeFramework                   x0000000104a6f1a0 _ZNK16KRefSharedHolder3refEv + 240
        at 5   MyNativeFramework                   0x0000000104a6eff4 -[KotlinBase release] + 48
        at 6   libobjc.A.dylib                     0x00000001aad36408 objc_release + 136
        at 7   PositionKit                         0x00000001044967e8 $s11PositionKit17MySensorC5startyyFySo14CMDeviceMotionCSg_s5Error_pSgtcfU_ + 684(lldb)

(names have been changed to protect closed source code)

What am I doing wrong? Do I have to somehow mark the float array as shared? I've read up on data freezing in Kotlin/Native but that only seems to apply to objects within the kotlin context.

Oxide

Answer 1

You have two exceptions here. The second one will be fixed in upcoming Kotlin 1.3.60 release.

The first one is likely caused by main thread accessing Kotlin object created on a background thread with an object expression (it could be sensorDataType), it could be MySensor instance. Freezing this object should help.

Estren

Thank you for your answer, I think it guided me in the right direction. sensorDataType is an enum, so that does make sense. I noticed I had failed to override two properties on the Swift side, however doing that did not fix the issue. How do I go about freezing an object? This tells me I should be able to call freeze() on any object, but trying to call it results in Unresolved reference: freeze even with an import on kotlin.native.concurrent.* – Oxide

The fact that sensorDataType is an enum gave me the idea that I was wrong in the details. An object requiring freezing is not sensorDataType but it is MySensor instance itself. kotlin.native.concurrent.* is Native-only, so it is available only in iOS source set of your project. – Estren

Any direction on how to freeze would be helpful! – Dasher

You don't need to freeze anything anymore, since there is the new memory manager in Kotlin/Native, and it is enabled by default since Kotlin 1.7.20. See more details here: kotlinlang.org/docs/… – Estren

What is meant by freezing an object? – Girand