问题描述
我正在处理一个 KMM 项目，目前正在开发一个模型层。为了处理数据，我计划像这样创建一个单例：
@ThreadLocal object Repository {
private var dao: DataAccessObject? = null
private val scope = Coroutinescope(dispatchers.Main)
fun injectDao(dao: DataAccessObject) {
scope.async {
Repository.dao = dao
}
}
suspend fun create(dataObjectType: TypeOfDataObject): DataObject? {
var dataObject: DataObject? = null
val job = scope.async {
dataObject = dao?.create(dataObjectType = dataObjectType)
}
job.await()
return dataObject
}
}
在您看到的这种实现中，对数据库的请求是在 Main 线程中处理的，这非常不好。但它有效并且数据从函数正确返回。下一个明显的步骤是尝试在后台范围内运行它。为了做到这一点，我们应该重新声明 scope:
private val scope = Coroutinescope(dispatchers.Default)
Uncaught Kotlin exception: kotlin.native.concurrent.InvalidMutabilityException: mutation attempt of frozen kotlin.native.internal.Ref@5761ad88
2021-02-02 23:54:50.408645+0300 Plendy[28960:2893398] [] nw_protocol_get_quic_image_block_invoke dlopen libquic Failed
at 0 Shared 0x000000010d51640f kfun:kotlin.Throwable#<init>(kotlin.String?){} + 95 (/Users/teamcity/buildAgent/work/f01984a9f5203417/runtime/src/main/kotlin/kotlin/Throwable.kt:23:37)
at 1 Shared 0x000000010d50f0bd kfun:kotlin.Exception#<init>(kotlin.String?){} + 93 (/Users/teamcity/buildAgent/work/f01984a9f5203417/runtime/src/main/kotlin/kotlin/Exceptions.kt:23:44)
at 2 Shared 0x000000010d50f32d kfun:kotlin.RuntimeException#<init>(kotlin.String?){} + 93 (/Users/teamcity/buildAgent/work/f01984a9f5203417/runtime/src/main/kotlin/kotlin/Exceptions.kt:34:44)
at 3 Shared 0x000000010d5448cd kfun:kotlin.native.concurrent.InvalidMutabilityException#<init>(kotlin.String){} + 93 (/Users/teamcity/buildAgent/work/f01984a9f5203417/runtime/src/main/kotlin/kotlin/native/concurrent/Freezing.kt:22:60)
at 4 Shared 0x000000010d5460af ThrowInvalidMutabilityException + 431 (/Users/teamcity/buildAgent/work/f01984a9f5203417/runtime/src/main/kotlin/kotlin/native/concurrent/Internal.kt:92:11)
at 5 Shared 0x000000010d6470b0 MutationCheck + 128
at 6 Shared 0x000000010d5640f8 kfun:kotlin.native.internal.Ref#<set-element>(1:0){} + 104 (/Users/teamcity/buildAgent/work/f01984a9f5203417/runtime/src/main/kotlin/kotlin/native/internal/Ref.kt:12:5)
at 7 Shared 0x000000010d4a1d5b kfun:com.plendy.PlendyCore.Model.KNPlendyData.$create$lambda-1COROUTINE$4.invokeSuspend#internal + 779 (/Users/petr/Documents/Projects/Plendy/Android/Plendy/PlendyCore/src/commonMain/kotlin/com/plendy/PlendyCore/Model/KNPlendyData.kt:23:13)
at 8 Shared 0x000000010d537958 kfun:kotlin.coroutines.native.internal.BaseContinuationImpl#resumeWith(kotlin.Result<kotlin.Any?>){} + 760 (/Users/teamcity/buildAgent/work/f01984a9f5203417/runtime/src/main/kotlin/kotlin/coroutines/ContinuationImpl.kt:30:39)
at 9 Shared 0x000000010d6d7a78 kfun:kotlinx.coroutines.dispatchedTask#run(){} + 2680 (/opt/buildAgent/work/44ec6e850d5c63f0/kotlinx-coroutines-core/common/src/internal/dispatchedTask.kt:106:71)
at 10 Shared 0x000000010d687fb8 kfun:kotlinx.coroutines.EventLoopImplBase#processNextEvent(){}kotlin.Long + 840 (/opt/buildAgent/work/44ec6e850d5c63f0/kotlinx-coroutines-core/common/src/EventLoop.common.kt:274:18)
at 11 Shared 0x000000010d6efbbb kfun:kotlinx.coroutines#runEventLoop(kotlinx.coroutines.EventLoop?;kotlin.Function0<kotlin.Boolean>){} + 843 (/opt/buildAgent/work/44ec6e850d5c63f0/kotlinx-coroutines-core/native/src/Builders.kt:80:40)
at 12 Shared 0x000000010d6f8d39 kfun:kotlinx.coroutines.WorkerCoroutinedispatcherImpl.start$lambda-0#internal + 409 (/opt/buildAgent/work/44ec6e850d5c63f0/kotlinx-coroutines-core/native/src/Workers.kt:49:17)
at 13 Shared 0x000000010d6f8f30 kfun:kotlinx.coroutines.WorkerCoroutinedispatcherImpl.$start$lambda-0$FUNCTION_REFERENCE$35.invoke#internal + 64 (/opt/buildAgent/work/44ec6e850d5c63f0/kotlinx-coroutines-core/native/src/Workers.kt:47:24)
at 14 Shared 0x000000010d6f8f90 kfun:kotlinx.coroutines.WorkerCoroutinedispatcherImpl.$start$lambda-0$FUNCTION_REFERENCE$35.$<bridge-UNN>invoke(){}#internal + 64 (/opt/buildAgent/work/44ec6e850d5c63f0/kotlinx-coroutines-core/native/src/Workers.kt:47:24)
at 15 Shared 0x000000010d545d59 WorkerLaunchpad + 185 (/Users/teamcity/buildAgent/work/f01984a9f5203417/runtime/src/main/kotlin/kotlin/native/concurrent/Internal.kt:69:54)
at 16 Shared 0x000000010d64ba4f _ZN6Worker19processQueueElementEb + 3135
at 17 Shared 0x000000010d64adf6 _ZN12_GLOBAL__N_113workerRoutineEPv + 54
at 18 libsystem_pthread.dylib 0x0000000110a86950 _pthread_start + 224
at 19 libsystem_pthread.dylib 0x0000000110a8247b thread_start + 15
奇怪的是，数据写入db，意味着dao被调用成功，但是数据没有从函数返回，因为异常发生得更早。此时我不明白异常与什么冻结对象有关？我接下来尝试的是删除 job.await() 行，它完美地工作，除了函数输出中的 null 原因之外没有任何例外。
所以我的问题是：如何让代码在后台线程中运行仍然能够等待其输出？
解决方法
您应该包含更多异常信息以帮助弄清楚发生了什么，并且您可以使用 ensureNeverFrozen 来帮助确定某些内容何时被无意冻结。不过，在这种情况下，我想我可以弄清楚。
在这种情况下，在后台 lambda 中捕获对 dataObject 的引用将冻结它。尝试重新分配它（可能）会抛出您的异常。
var dataObject: DataObject? = null
val job = scope.async {
//Trying to assign the frozen dataObject will fail
dataObject = dao?.create(dataObjectType = dataObjectType)
}
既然您已经在挂起函数中，为什么不直接使用 withContext 之类的东西？
suspend fun create(dataObjectType: TypeOfDataObject): DataObject? {
val dataObject = withContext(Dispatchers.Default) {
dao?.create(dataObjectType = dataObjectType)
}
return dataObject
}
如果你走那么远......
suspend fun create(dataObjectType: TypeOfDataObject): DataObject? = withContext(Dispatchers.Default) {
dao?.create(dataObjectType = dataObjectType)
}