1. Space-Time Memory Kishore Ramachandran Georgia Tech Joint work with researchers from Compaq CRL (Rishiyur Nikhil, Jim Rehg, Bert Halstead, Chris Joerg, Leonidas Kontothanassis and Kath Knobe) a concurrent dynamic data structure for flexible manipulation of time-sequenced data, with automatic GC

2. Interactive Stream-Oriented Apps vision, animation, multimedia collaboration Why parallel computing for such apps? computationally intensive inherently parallel (pipelined, data, and task) Platforms? SMPs, and clusters Problems dynamic data sharing real-time properties

3. CRL’s Smart Kiosk Application public access to info and entertainment multiple users interact with multiple Kiosks input: implicit (camera, gaze, infrared,...) and explicit (voice, gesture, touch-screen,...) output: emotive face, synthesized speech,... digitizer tracker input nettracker output net.... decision heterogeneous pieces of software: GUIs, trackers, etc.

4. What new issues? temporally evolving dynamic data structures dynamic producer-consumer relationships not everything consumed inter-stream synchronization digitizer Hi-Fi tracker Low-Fi tracker buffers time

5. Concurrent dynamic data structure Space-Time Memory............ 1 2 3 4. 1 2 3 4... space time threads connections channels

6. An Example chan1 chan2 chan3 space Digitizer Hi-Fi tracker Low-Fi tracker t1 t2 t3 t4 t5 virtual time... space-time memory D_t1 H-t1 L_t1

7. Using the STM consumer: get-item(in-connection, ts) code to use item consume-item(in-connection, ts) in-connection ThreadThread channel out-connection producer: put-item(out-connection, ts) channel API includes calls to: create channel connect, disconnect to/from channel advance thread virtual time synchronize virtual time with real time

8. Summary STM, a concurrent dynamic data structure for flexible manipulation of time-sequenced data, with automatic GC Why is STM a good idea? –time: important attribute for interactive apps –sharing abstractions such as DSM, and synchronization abstractions such as locks and barriers are too low level –current parallel programming languages do not offer the right abstractions for stream-oriented interactive apps.