Building the Java Heap with Bricks in an Embedded Real-Time Environment

The allocation and de-allocation of objects different sized causes the external fragmentation problem. To deal with external fragmentation, we can use a copy-based Garbage Collector (GC) or a non-copying based GC with a compaction phase. Both require move and relocate objects. Copying or scanning big objects or large arrays incurs also large unpredictable collector pause times, making it impossible to guarantee real-time deadlines. One possible solution to offer acceptable bounds for both collection time and space, is to put a limit on object sizes. This solution allows us to calculate the maximal pause time of the collector and the bound of the GC latency. In order to meet space efficiency and time predictability, this paper proposes an object layout, which divides the object into blocks of the same size, avoiding fragmentation and allowing the collector to work with blocks of the same size.