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wcf-avoid-endless-recursion-in-two-iworkflowinstancemanagement-apis.md

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Avoiding endless recursion for IWorkflowInstanceManagement.TransactedCancel and IWorkflowInstanceManagement.TransactedTerminate

Scope

Edge

Version Introduced

4.7.2

Source Analyzer Status

NotPlanned

Change Description

Under some circumstances when using xref:System.ServiceModel.Activities.IWorkflowInstanceManagement.TransactedCancel%2A?displayProperty=nameWithType or xref:System.ServiceModel.Activities.IWorkflowInstanceManagement.TransactedTerminate%2A?displayProperty=nameWithType APIs to cancel or terminate a worklow service instance, the workflow instance may encounter a stack overflow due to endless recursion when the Workflow runtime attempts to persist the service instance as part of processing the request. The problem occurs if the workflow instance is in a state where it is waiting for some other outstanding WCF request to another service to complete.

The TransactedCancel and TransactedTerminate operations create work items that are queued for the workflow service instance. These work items are not executed as part of the processing of the TransactedCancel/TransactedTerminate request. Because the workflow service instance is busy waiting for the other outstanding WCF request to complete, the work item created remains queued. The TransactedCancel/TransactedTerminate operation completes and control is returned back to the client. When the transaction associated with the TransactedCancel/TransactedTerminate operation attempts to commit, it needs to persist the workflow serivce instance state. But because there is an outstanding WCF request for the instance, the Workflow runtime cannot persist the workflow service instance, and an endless recursion loop leads to the stack overflow.

Because TransactedCancel and TransactedTerminate only create a work item in memory, the fact that a transaction exists doesn't have any effect. A rollback of the transaction does not discard the work item.

To address this issue, starting in .NET Framework 4.7.2, we have introduced an AppSetting that can be added to the web.config/app.config of the workflow service that tells it to ignore transactions for TransactedCancel and TransactedTerminate. This allows the transaction to commit without waiting for the workflow instance to persist.

The AppSetting for this feature is named microsoft:WorkflowServices:IgnoreTransactionsForTransactedCancelAndTransactedTerminate. A value of true indicates that the transaction should be ignored, thus avoiding the stack overflow. The default value of this AppSetting is false, so existing workflow service instances are not affected.

  • Quirked
  • Build-time break

Recommended Action

If you are using AppFabric or another xref:System.ServiceModel.Activities.IWorkflowInstanceManagement client and are encountering a stack overflow in the workflow serivce instance when trying to cancel or terminate a workflow instance, you can add the following to the <appSettings> section of the web.config/app.config file for the workflow service:

  <add key="microsoft:WorkflowServices:IgnoreTransactionsForTransactedCancelAndTransactedTerminate" value="true"/>

If you are not encountering the problem, you do not need to do this.

Affected APIs

  • Not detectable via API analysis

Category

Windows Workflow Foundation (WF)