DefaultGCExchangeFacadeSessionProvider.openSession broken when called concurrently from multiple workflows

[ahubold]

DefaultGCExchangeFacadeSessionProvider.openSession uses a java.lang.ServiceLoader to find GCExchangeFacadeProvider implementations. The ServiceLoader instance is used concurrently, if the method is called by multiple concurrently running workflow actions.

ServiceLoader however must not be used concurrently. From its Javadoc:

Instances of this class are not safe for use by multiple concurrent threads.

This can lead to NoSuchElementExceptions or not found implementations, which in turn lead to escalated workflows.

2021-05-19 08:03:12 - [WARN] com.coremedia.cap.workflow.plugin.LongActionBase [] - exception occurred in LongActionBase, will pass as result (LongActionManager-2 for coremedia:///cap/task/477873/477881)
java.util.NoSuchElementException: null
at java.base/java.lang.CompoundEnumeration.nextElement(Unknown Source)
at java.base/java.util.ServiceLoader$LazyClassPathLookupIterator.nextProviderClass(Unknown Source)
at java.base/java.util.ServiceLoader$LazyClassPathLookupIterator.hasNextService(Unknown Source)
at java.base/java.util.ServiceLoader$LazyClassPathLookupIterator.hasNext(Unknown Source)
at java.base/java.util.ServiceLoader$2.hasNext(Unknown Source)
at java.base/java.util.ServiceLoader$3.hasNext(Unknown Source)
at com.coremedia.labs.translation.gcc.facade.DefaultGCExchangeFacadeSessionProvider.openSession(DefaultGCExchangeFacadeSessionProvider.java:40)
at com.coremedia.labs.translation.gcc.workflow.GlobalLinkAction.openSession(GlobalLinkAction.java:430)
at com.coremedia.labs.translation.gcc.workflow.GlobalLinkAction.doExecute(GlobalLinkAction.java:202)
at com.coremedia.labs.translation.gcc.workflow.GlobalLinkAction.doExecute(GlobalLinkAction.java:84)
...
2021-05-19 08:03:12 - [WARN] com.coremedia.labs.translation.gcc.workflow.GlobalLinkAction [] - com.coremedia.labs.translation.gcc.workflow.DownloadFromGlobalLinkAction: Unknown error occurred (GCC-WF-10000) (LongActionManager-3 for coremedia:///cap/task/494864/494872)
com.coremedia.labs.translation.gcc.facade.GCFacadeException: No GCExchange facade available as default/fallback.
at com.coremedia.labs.translation.gcc.facade.DefaultGCExchangeFacadeSessionProvider.openSession(DefaultGCExchangeFacadeSessionProvider.java:50)
at com.coremedia.labs.translation.gcc.workflow.GlobalLinkAction.openSession(GlobalLinkAction.java:430)
at com.coremedia.labs.translation.gcc.workflow.GlobalLinkAction.doExecute(GlobalLinkAction.java:202)
at com.coremedia.labs.translation.gcc.workflow.GlobalLinkAction.doExecute(GlobalLinkAction.java:84)
at com.coremedia.cap.workflow.plugin.LongActionBase.execute(LongActionBase.java:91)