The Return Processing field designates which option flag will be used to control the processing of the custom action thread. You can edit your selection by clicking the field in the custom action property grid and selecting from the following options in the drop-down menu:

- Asynchronous (No wait for completion)
- Asynchronous (Wait for exit code)
- Synchronous (Check exit code)
- Synchronous (Ignores exit code)

These flags are used to specify that the main and custom action threads run synchronously (the installer waits for the custom action thread to complete before resuming the main installation thread) or asynchronously (the installer runs the custom action simultaneously as the main installation continues).