I recently updated a CDT, which is referenced in a process model subprocess. The

Hi Daniel, We've done a lot of versioning of CDTs over the last few years, and have as a result gone back through our workflows and removed most passing by reference because of the sorts of issues you are experiencing.
If you instead passs the parameter by value on input and map it on output, you don't get the problem (in this case, Appian is smart enough to auto-convert most CDT changes).
This is a shame, because you lose the benefits of by reference passing (performance / memory usage / simplicity). Given Appian can auto convert CDTs when passed by value, it would certainly be a good improvement if it also did it when passed by reference.
There are still a few cases we use passing by reference, but only when we know the subprocess we are calling will ALWAYS return quickly (ie: has no user tasks, msg task, scheduled tasks, etc). That way their will never be running instances of them when you upgrade.

Hi Daniel, We've done a lot of versioning of CDTs over the last few years, and have as a result gone back through our workflows and removed most passing by reference because of the sorts of issues you are experiencing.
If you instead passs the parameter by value on input and map it on output, you don't get the problem (in this case, Appian is smart enough to auto-convert most CDT changes).
This is a shame, because you lose the benefits of by reference passing (performance / memory usage / simplicity). Given Appian can auto convert CDTs when passed by value, it would certainly be a good improvement if it also did it when passed by reference.
There are still a few cases we use passing by reference, but only when we know the subprocess we are calling will ALWAYS return quickly (ie: has no user tasks, msg task, scheduled tasks, etc). That way their will never be running instances of them when you upgrade.