According to the present disclosure, one or more processors of a computer device (e.g. a mobile communication device) are operative to execute a garbage collection program and an application program concurrently with execution of the garbage collection program. The garbage collection program is operative to identify a root set of referenced objects of an application program, where a reference indicator in a reference indicator array is set as referenced for each one of such referenced objects, and to perform a mark and sweep process based on the root set of referenced objects. The application program has computer instructions which includes a predefined computer instruction (e.g. a GETREF instruction) adapted to retrieve a reference from a target object and to set a reference indicator in the reference indicator array as referenced for the target object when executed. Advantageously, execution of the application program need not be unreasonably suspended during garbage collection processes. In one illustrative example, the application program is adapted to receive and/or provide information via a user interface of the computer device, and the concurrent processing allows for the receiving and/or providing of the information via the user interface without interference (e.g. suspension or delay) during the mark and sweep process.