Lecture Notes for Client-Server Interfaces

15 March 2001 - Single-Threaded Concurrency

1. one computation, many requests

2. multiplex the computation over the requests

   1. simple requests imply trivial multiplexing

   2. "simple" means short

   3. long requests are not so simple

3. why bother

   1. simplicity - no synchronization or communication (sorta)

   2. improved performance - low overhead

4. multiplexing sockets - asynchronous io

5. this is event-driven (or data-driven) programming

   1. io events

   2. timer events - time-outs, heartbeats

   3. could use alarm signals - complex and insecure

   4. fortunately, select() can combine time and io

   5. implementation

      1. keep a priority queue of timer events, nearest deadlines first

      2. the head of the queue determines the select() time-out

      3. on select() time-out, deal with the time-out event

      4. time-out events are function pointers.

   6. interface

      1. schedule a function call to occur

      2. cancel a scheduled function call

      3. respond to the time-out

This page last modified on 10 April 2001.