你见过 ConcurrentHashMap 使用不当报错 java.lang.IllegalStateException: Recursive update 吗？

最新推荐文章于 2024-04-20 15:23:14 发布

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最新推荐文章于 2024-04-20 15:23:14 发布 · 2.3k 阅读

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#java #哈希 #数据结构

本文探讨了在Java中遇到的`java.util.ConcurrentModificationException`异常，特别是在ShardingSphere项目中出现的`java.lang.IllegalStateException:Recursiveupdate`问题。文章详细介绍了问题背景，分析了`ConcurrentHashMap`的源码，指出递归更新导致的问题，并通过对比HashMap的行为解释了为何`ConcurrentModificationException`会出现。最后，文章提出了问题的修复策略，避免在使用`ConcurrentHashMap`的`computeIfAbsent`时发生递归调用。

了解 Java 的同学，也许会见过一个异常 java.util.ConcurrentModificationException，这个一般在迭代器访问 Collection、Map 等数据结构过程中，修改了数据结构中的元素导致。
前段时间，ShardingSphere 遇到一个偶发报错的问题：java.lang.IllegalStateException: Recursive update。这个问题其实和并发修改问题有相似之处。本文主要记录该问题的排查与分析过程。

文章目录

问题背景

Apache ShardingSphere 在 Proxy 模块重构后的一段时间里，频繁发生偶发报错 java.lang.IllegalStateException: Recursive update。

引发该问题的重构 PR：https://github.com/apache/shardingsphere/pull/24251

java.util.ServiceConfigurationError: org.apache.shardingsphere.proxy.backend.mysql.handler.admin.MySQLSessionVariableHandler: Provider org.apache.shardingsphere.proxy.backend.mysql.handler.admin.MySQLDefaultSessionVariableHandler could not be instantiated

	at java.base/java.util.ServiceLoader.fail(ServiceLoader.java:586)
	at java.base/java.util.ServiceLoader$ProviderImpl.newInstance(ServiceLoader.java:813)
	at java.base/java.util.ServiceLoader$ProviderImpl.get(ServiceLoader.java:729)
	at java.base/java.util.ServiceLoader$3.next(ServiceLoader.java:1403)
	at org.apache.shardingsphere.infra.util.spi.ShardingSphereServiceLoader.load(ShardingSphereServiceLoader.java:56)
	at org.apache.shardingsphere.infra.util.spi.ShardingSphereServiceLoader.<init>(ShardingSphereServiceLoader.java:46)
	at java.base/java.util.concurrent.ConcurrentHashMap.computeIfAbsent(ConcurrentHashMap.java:1708)
	at org.apache.shardingsphere.infra.util.spi.ShardingSphereServiceLoader.getServiceInstances(ShardingSphereServiceLoader.java:73)
	at org.apache.shardingsphere.infra.util.spi.type.typed.TypedSPILoader.findService(TypedSPILoader.java:71)
	at org.apache.shardingsphere.infra.util.spi.type.typed.TypedSPILoader.getService(TypedSPILoader.java:126)
	at org.apache.shardingsphere.infra.util.spi.type.typed.TypedSPILoader.getService(TypedSPILoader.java:113)
	at org.apache.shardingsphere.proxy.backend.mysql.handler.admin.MySQLSetVariableAdminExecutor.lambda$execute$0(MySQLSetVariableAdminExecutor.java:56)
	at java.base/java.util.stream.Collectors.lambda$uniqKeysMapAccumulator$1(Collectors.java:180)
	at java.base/java.util.stream.ReduceOps$3ReducingSink.accept(ReduceOps.java:169)
	at java.base/java.util.HashMap$KeySpliterator.forEachRemaining(HashMap.java:1715)
	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:509)
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:499)
	at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:921)
	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:682)
	at org.apache.shardingsphere.proxy.backend.mysql.handler.admin.MySQLSetVariableAdminExecutor.execute(MySQLSetVariableAdminExecutor.java:56)
	at org.apache.shardingsphere.proxy.backend.mysql.handler.admin.executor.MySQLSetVariableAdminExecutorTest.assertExecute(MySQLSetVariableAdminExecutorTest.java:66)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
	at java.base/java.lang.reflect.Method.invoke(Method.java:578)
	at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:727)
	... 省略 JUnit 调用栈
Caused by: java.lang.IllegalStateException: Recursive update
	at java.base/java.util.concurrent.ConcurrentHashMap.computeIfAbsent(ConcurrentHashMap.java:1763)
	at org.apache.shardingsphere.infra.util.spi.ShardingSphereServiceLoader.getServiceInstances(ShardingSphereServiceLoader.java:73)
	at org.apache.shardingsphere.infra.util.spi.type.typed.TypedSPILoader.findService(TypedSPILoader.java:71)
	at org.apache.shardingsphere.infra.util.spi.type.typed.TypedSPILoader.findService(TypedSPILoader.java:55)
	at org.apache.shardingsphere.proxy.backend.handler.admin.executor.DefaultSessionVariableHandler.<init>(DefaultSessionVariableHandler.java:36)
	at org.apache.shardingsphere.proxy.backend.mysql.handler.admin.MySQLDefaultSessionVariableHandler.<init>(MySQLDefaultSessionVariableHandler.java:28)
	at java.base/jdk.internal.reflect.DirectConstructorHandleAccessor.newInstance(DirectConstructorHandleAccessor.java:67)
	at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:500)
	at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:484)
	at java.base/java.util.ServiceLoader$ProviderImpl.newInstance(ServiceLoader.java:789)
	... 88 more

抛异常的是 ConcurrentHashMap 实例是以下的 LOADERS</