A proxy server containing a cache for retrieving information from a server and transmitting this information to multiple concurrent clients. A thread is created for each client requesting the information from the server. As long as information is contained in the cache, all the threads assume the role of a consumer thread by retrieving this information from the cache and placing it in an output stream to be sent to the client associated with each consumer thread. When one of the threads reaches the end of the information contained in the cache, it assumes the role of a producer to send a request to the server to retrieve additional information. When the producer thread receives the information from the server, it places it in an input stream for the cache. The producer thread then reverts back to a consumer thread to retrieve this information for its associated client. All other consumer threads may also retrieve this data from the cache. In retrieving information from the server, there may be multiple producers and consumers, however it is preferable that only one thread will be a producer at any given time.

Bounding delays and reducing threading overheads in caching

Shared memory machines have two major overheads: keeping caches coherent and managing the multiple threads of computation which enable tolerance of very long memory latencies. Thetis is a hybrid architecture providing both shared memory and efficient message passing; it will be built from 'commodity' components and consists of sites with a small number of computation processors and a separate, programmable, auxiliary processor. The auxiliary processor performs overhead tasks, e.g. maintenance of cache directories, management of memory and thread queues; placed on its own bus, it does not block or delay memory accesses from computation processors which are not waiting for it. We describe how the use of a threaded variant of C (which has a functional style) enables the run-time system to dynamically determine coherence needs-dramatically reducing the overhead of maintaining coherent caches in a shared memory machine.

J. Morris

Papers

Reducing overheads in distributed shared memory systems