Region-based garbage collectors offer a reduction in average application
pause times (or even maximum pause time guarantees for real time
systems) by placing bounds on the amount of work a garbage collector
must perform each collection cycle. The heap is typically partitioned
into regions containing a subset of objects on the heap. Arrays,
however, can be arbitrarily long and can exceed the size of an
individual region, defeating the benefits (or guarantees) of a
region-based collector. To counter that, arrays can be fragmented
into multiple, discontiguous arraylets that are sized to fit within
a region and can be processed independently. While they are an
effective solution to maintain lower pause times, their non-contiguous
representation poses challenges for compiler optimizations and memory
access throughput. This talk will discuss these challenges and describe
an efficient hybrid arraylet representation that allows arrays to have
a contiguous-discontiguous duality. Modifications to a Just-In-Time
compiler to efficiently handle arrays of either shape will be presented.