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通过引入防御性复制以避免ConcurrentModificationException

· 2 min read
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programmer on jvm platform

在consul中修改相关服务的配置时引发ConcurrentModificationException并导致协程任务异常退出.
相关报错如下:

2022-11-24 10:08:27.954  INFO 1 --- [TaskScheduler-1] b.c.PropertySourceBootstrapConfiguration : Located property source: [BootstrapPropertySource {name='bootstrapProperties-config/mgmt-scheduler/'}, BootstrapPropertySource {name='bootstrapProperties-config/application/'}]
2022-11-24 10:08:27.968  INFO 1 --- [TaskScheduler-1] o.s.boot.SpringApplication               : No active profile set, falling back to 1 default profile: "default"
2022-11-24 10:08:27.979  INFO 1 --- [TaskScheduler-1] o.s.boot.SpringApplication               : Started application in 0.244 seconds (JVM running for 7930.38)
Exception in thread "DefaultDispatcher-worker-6" java.util.ConcurrentModificationException
at java.base/java.util.ArrayList$Itr.checkForComodification(ArrayList.java:1013)
at java.base/java.util.ArrayList$Itr.next(ArrayList.java:967)
at com.fastonetech.scheduling.core.ResourceDispatcher$Companion$of$1$1.invokeSuspend(ResourceDispatcher.kt:40)
at com.fastonetech.scheduling.core.ResourceDispatcher$Companion$of$1$1.invoke(ResourceDispatcher.kt)
at com.fastonetech.scheduling.core.ResourceDispatcher$Companion$of$1$1.invoke(ResourceDispatcher.kt)
at kotlinx.coroutines.intrinsics.UndispatchedKt.startUndispatchedOrReturn(Undispatched.kt:89)
at kotlinx.coroutines.CoroutineScopeKt.coroutineScope(CoroutineScope.kt:264)
at com.fastonetech.scheduling.core.ResourceDispatcher$Companion$of$1.dispatch(ResourceDispatcher.kt:16)
at com.fastonetech.scheduling.core.ResourceDispatcher$Companion$of$3.schedule(ResourceDispatcher.kt:32)
at com.fastonetech.scheduling.core.ResourceDispatcher$Companion$of$3.schedule(ResourceDispatcher.kt:27)
at com.fastonetech.scheduling.core.ResourceDispatcher$Companion$of$1$1$2$1.invokeSuspend(ResourceDispatcher.kt:19)
at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
at kotlinx.coroutines.internal.LimitedDispatcher.run(LimitedDispatcher.kt:42)
at kotlinx.coroutines.scheduling.TaskImpl.run(Tasks.kt:95)
at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:570)
at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:749)
at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:677)
at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:664)
Suppressed: kotlinx.coroutines.DiagnosticCoroutineContextException: [StandaloneCoroutine{Cancelling}@19b8b4b6, Dispatchers.IO]

原因​

这个问题的原因是被修改的配置映射到了代码中被@ConfigurationProperties注解的类中的一个List类型的属性.
该属性被修改时恰好协程任务正在遍历该属性, 从而导致ConcurrentModificationException异常.

解决方案​

每次获取该属性时都进行一次防御性复制, 从而避免ConcurrentModificationException异常

参考资料​