Validation snapshot generation is not thread safe

[delopst]

When the HAPI FHIR server is started and you try to create/update multiple resources on multiple threads snapshot generation fails on some threads. After the snapshot is generated and cached things are working fine.

This is the exception when this happens.

Caused by: java.util.ConcurrentModificationException
  at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:1013) ~[?:?]
  at java.util.ArrayList$Itr.next(ArrayList.java:967) ~[?:?]
  at org.hl7.fhir.convertors.conv40_50.resources40_50.StructureDefinition40_50.convertStructureDefinitionSnapshotComponent(StructureDefinition40_50.java:365) ~[org.hl7.fhir.convertors-6.0.1.jar:?]
  at org.hl7.fhir.convertors.conv40_50.resources40_50.StructureDefinition40_50.convertStructureDefinition(StructureDefinition40_50.java:105) ~[org.hl7.fhir.convertors-6.0.1.jar:?]
  at org.hl7.fhir.convertors.conv40_50.resources40_50.Resource40_50.convertResource(Resource40_50.java:245) ~[org.hl7.fhir.convertors-6.0.1.jar:?]
  at org.hl7.fhir.convertors.conv40_50.VersionConvertor_40_50.convertResource(VersionConvertor_40_50.java:77) ~[org.hl7.fhir.convertors-6.0.1.jar:?]
  at org.hl7.fhir.convertors.factory.VersionConvertorFactory_40_50.convertResource(VersionConvertorFactory_40_50.java:15) ~[org.hl7.fhir.convertors-6.0.1.jar:?]
  at ca.uhn.hapi.converters.canonical.VersionCanonicalizer$R4Strategy.resourceToValidatorCanonical(VersionCanonicalizer.java:750) ~[hapi-fhir-converter-6.6.0.jar:?]
  at ca.uhn.hapi.converters.canonical.VersionCanonicalizer.resourceToValidatorCanonical(VersionCanonicalizer.java:263) ~[hapi-fhir-converter-6.6.0.jar:?]
  at org.hl7.fhir.common.hapi.validation.validator.VersionSpecificWorkerContextWrapper.lambda$new$0(VersionSpecificWorkerContextWrapper.java:96) ~[hapi-fhir-validation-6.6.0.jar:?]
  at com.github.benmanes.caffeine.cache.LocalLoadingCache.lambda$newMappingFunction$2(LocalLoadingCache.java:145) ~[caffeine-2.9.3.jar:?]
  at com.github.benmanes.caffeine.cache.BoundedLocalCache.lambda$doComputeIfAbsent$14(BoundedLocalCache.java:2406) ~[caffeine-2.9.3.jar:?]
  at java.util.concurrent.ConcurrentHashMap.compute(ConcurrentHashMap.java:1916) ~[?:?]
  at com.github.benmanes.caffeine.cache.BoundedLocalCache.doComputeIfAbsent(BoundedLocalCache.java:2404) ~[caffeine-2.9.3.jar:?]
  at com.github.benmanes.caffeine.cache.BoundedLocalCache.computeIfAbsent(BoundedLocalCache.java:2387) ~[caffeine-2.9.3.jar:?]
  at com.github.benmanes.caffeine.cache.LocalCache.computeIfAbsent(LocalCache.java:108) ~[caffeine-2.9.3.jar:?]
  at com.github.benmanes.caffeine.cache.LocalLoadingCache.get(LocalLoadingCache.java:56) ~[caffeine-2.9.3.jar:?]
  at ca.uhn.fhir.sl.cache.caffeine.LoadingCacheDelegator.get(LoadingCacheDelegator.java:39) ~[hapi-fhir-caching-caffeine-6.6.0.jar:?]
  at org.hl7.fhir.common.hapi.validation.validator.VersionSpecificWorkerContextWrapper.fetchResource(VersionSpecificWorkerContextWrapper.java:352) ~[hapi-fhir-validation-6.6.0.jar:?]
  at org.hl7.fhir.common.hapi.validation.validator.ValidatorWrapper.fetchAndAddProfile(ValidatorWrapper.java:216) ~[hapi-fhir-validation-6.6.0.jar:?]
  at org.hl7.fhir.common.hapi.validation.validator.ValidatorWrapper.validate(ValidatorWrapper.java:184) ~[hapi-fhir-validation-6.6.0.jar:?]
  at org.hl7.fhir.common.hapi.validation.validator.FhirInstanceValidator.validate(FhirInstanceValidator.java:238) ~[hapi-fhir-validation-6.6.0.jar:?]
  at org.hl7.fhir.common.hapi.validation.validator.BaseValidatorBridge.doValidate(BaseValidatorBridge.java:22) ~[hapi-fhir-validation-6.6.0.jar:?]
  at org.hl7.fhir.common.hapi.validation.validator.BaseValidatorBridge.validateResource(BaseValidatorBridge.java:48) ~[hapi-fhir-validation-6.6.0.jar:?]
  at org.hl7.fhir.common.hapi.validation.validator.FhirInstanceValidator.validateResource(FhirInstanceValidator.java:26) ~[hapi-fhir-validation-6.6.0.jar:?]
  at ca.uhn.fhir.validation.FhirValidator.validateResource(FhirValidator.java:342) ~[hapi-fhir-base-6.6.0.jar:?]
  at ca.uhn.fhir.validation.FhirValidator.doValidate(FhirValidator.java:263) ~[hapi-fhir-base-6.6.0.jar:?]
  at ca.uhn.fhir.validation.FhirValidator.validateWithResult(FhirValidator.java:251) ~[hapi-fhir-base-6.6.0.jar:?]
  at ca.uhn.fhir.validation.FhirValidator.validateWithResult(FhirValidator.java:210) ~[hapi-fhir-base-6.6.0.jar:?]
  at ca.uhn.fhir.jpa.interceptor.validation.RequireValidationRule.evaluate(RequireValidationRule.java:79) ~[hapi-fhir-storage-6.6.0.jar:?]
  at ca.uhn.fhir.jpa.interceptor.validation.RepositoryValidatingInterceptor.handle(RepositoryValidatingInterceptor.java:139) ~[hapi-fhir-storage-6.6.0.jar:?]
  at ca.uhn.fhir.jpa.interceptor.validation.RepositoryValidatingInterceptor.update(RepositoryValidatingInterceptor.java:129) ~[hapi-fhir-storage-6.6.0.jar:?]
  at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:?]
  at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77) ~[?:?]
  at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:?]
  at java.lang.reflect.Method.invoke(Method.java:568) ~[?:?]
  at ca.uhn.fhir.interceptor.executor.BaseInterceptorService$HookInvoker.invoke(BaseInterceptorService.java:517) ~[hapi-fhir-base-6.6.0.jar:?]
  at ca.uhn.fhir.interceptor.executor.BaseInterceptorService.doCallHooks(BaseInterceptorService.java:281) ~[hapi-fhir-base-6.6.0.jar:?]
  at ca.uhn.fhir.interceptor.executor.BaseInterceptorService.callHooks(BaseInterceptorService.java:269) ~[hapi-fhir-base-6.6.0.jar:?]
  at ca.uhn.fhir.interceptor.executor.BaseInterceptorService.callHooks(BaseInterceptorService.java:63) ~[hapi-fhir-base-6.6.0.jar:?]
  at ca.uhn.fhir.rest.server.util.CompositeInterceptorBroadcaster$1.callHooks(CompositeInterceptorBroadcaster.java:72) ~[hapi-fhir-server-6.6.0.jar:?]
  at ca.uhn.fhir.rest.server.util.CompositeInterceptorBroadcaster$1.callHooks(CompositeInterceptorBroadcaster.java:63) ~[hapi-fhir-server-6.6.0.jar:?]
  at ca.uhn.fhir.rest.server.util.CompositeInterceptorBroadcaster.doCallHooks(CompositeInterceptorBroadcaster.java:43) ~[hapi-fhir-server-6.6.0.jar:?]
  at ca.uhn.fhir.jpa.dao.BaseStorageDao.doCallHooks(BaseStorageDao.java:365) ~[hapi-fhir-storage-6.6.0.jar:?]
  at ca.uhn.fhir.jpa.dao.BaseHapiFhirDao.notifyInterceptors(BaseHapiFhirDao.java:1464) ~[hapi-fhir-jpaserver-base-6.6.0.jar:?]
  at ca.uhn.fhir.jpa.dao.BaseHapiFhirDao.updateInternal(BaseHapiFhirDao.java:1383) ~[hapi-fhir-jpaserver-base-6.6.0.jar:?]
  at ca.uhn.fhir.jpa.dao.BaseStorageResourceDao.doUpdateForUpdateOrPatch(BaseStorageResourceDao.java:214) ~[hapi-fhir-storage-6.6.0.jar:?]
  at ca.uhn.fhir.jpa.dao.BaseHapiFhirResourceDao.doUpdateForUpdateOrPatch(BaseHapiFhirResourceDao.java:1900) ~[hapi-fhir-jpaserver-base-6.6.0.jar:?]
  at ca.uhn.fhir.jpa.dao.BaseHapiFhirResourceDao.doUpdate(BaseHapiFhirResourceDao.java:1886) ~[hapi-fhir-jpaserver-base-6.6.0.jar:?]
  at ca.uhn.fhir.jpa.dao.BaseHapiFhirResourceDao.lambda$update$21(BaseHapiFhirResourceDao.java:1806) ~[hapi-fhir-jpaserver-base-6.6.0.jar:?]
  at ca.uhn.fhir.jpa.dao.tx.HapiTransactionService.invokeCallableAndHandleAnyException(HapiTransactionService.java:458) ~[hapi-fhir-storage-6.6.0.jar:?]
  ... 116 more  

This is an attempt to make this thread-safe. Hope it helps you :)

Best regards, Primož