Starting with 4Dv15 R5, the 4D language can be ran in preemptive processes. There are only certain commands that can be ran in a preemptive process and some commands cannot. However with methods, which are designer defined, the ability to run the methods in a preemptive process or not is allowed to be set by the designer too.

This is done by navigating to the specific method's method properties from the Explorer going to the method and performing a contextual click on the method name and selecting 'Method Properties...'
This will bring up the Method Properties window. Starting with 4Dv15 R5 a new 'Execution mode' section is added which is not seen in the prior version as shown below.

4Dv15R4 and below:


4Dv15R5 and above:


Methods are set as 'Indifferent' as default.