Do not use parallel execution within plug-ins and workflow activities

Category: Design, Performance, Security, Supportability

Impact potential: High


Multi-threading or parallel calls within plug-ins or custom workflow activities can cause corruption of those the connections. As an example, executing parallel threads can log exceptions such as:

Generic SQL error. The transaction active in this session has been committed or aborted by another session.

Also, non-thread safe objects such as items in the System.Collections Namespace can become corrupted by parallel threads.


The sandbox service has been designed to execute calls in a specific order as part of a transaction. Developing plug-ins or custom workflow activities to make parallel or multi-threaded calls is not supported. Develop your plug-ins and custom workflow activities knowing that the calls will be performed sequentially and may need to be rolled back.


Using parallel execution from a client program is a supported practice to optimize performance as needed. This guidance is specific to code written to be executed within a plug-in or custom workflow activity.

Problematic patterns

Plug-ins and custom workflow activities run within a single transaction and multiple threads introduced by parallel execution can corrupt the transaction. The following are examples of patterns and practices that should not be used within plug-ins and custom workflow activities:

Additional information

Using and updating shared pipeline context objects could cause these objects to contain unexpected results or become corrupted. The affect of this would be a failure in the plug-in or custom workflow activity.

See also

Parallel Processing, Concurrency, and Async Programming in .NET