Dead Timestamp Identification in Stampede

Stampede is a parallel programming system to support computationally demanding applications including interactive vision, speech and multimedia collaboration. The system alleviates concerns such as communication, synchronization, and buffer management in programming such realtime stream-oriented applications. Threads are loosely connected by channels which hold streams of items, each identified by a timestamp. There are two performance concerns when programming with Stampede. The first is space, namely, ensuring that memory is not wasted on items bearing a timestamp that is not fully processed. The second is time, namely, ensuring that processing resource is not wasted on a timestamp that is not fully processed. In this paper we introduce a single unifying framework, dead timestamp identification, that addresses both the space and time concerns simultaneously. Dead timestamps on a channel represent garbage. Dead timestamps at a thread represent computations that need not be performed. This framework has been implemented in the Stampede system. Experimental results showing the space advantage of this framework are presented. Using a color-based people tracker application, we show that the space advantage can be significant (up to 40%) compared to the previous GC techniques