A compacting incremental collector and its performance in a production quality compiler

Abstract

We present a new near-real-time compacting collector and its implementation in a production quality Scheme compiler (Gambit-C). Our goal is to use this system as a base for an implementation of Erlang for writing soft real-time telecommunication applications. We start with a description of Gambit-C's memory organisation and its blocking collector. The design and integration of the incremental collector within Gambit-C are then explained. Finally we measure the performance of the incremental collector and compare it to the original blocking collector. We found that the overhead of the incremental collector is high (a factor of 1.3 to 8.1, with a median of 2.24) but nevertheless the collection pauses are compatible with typical soft real-time requirements (we get an average pause of 2.9 milliseconds and a maximum pause of 15 milliseconds on a 133Mhz DEC Alpha 21064).