1. Distributed Systems 2 Distributed Processing

2. Process A process is a logical representation of a physical processor that executes program code and has associated state and data. Can have separate address space Processing created by running app or language construct (e.g.fork) Operating system carries out a context switch Processes that share data – lightweight processes or threads

3. Co-operation Why is cooperation required ?

4. Synchronization On the same computer – fairly easy. Shared clock and can share memory. Semaphores are one method  WAIT(sem-name)  SIGNAL(sem-name) Semaphores can be used in the solution of class distributed processing problem – the Dining Philosophers

5. Dangers of Synchronization Starvation Deadlock

6. Other kinds of interprocess synchronization Eventcounts  ADVANCE(count-name)  READ(count-name)  AWAIT(count-name, value) Similar to the coordination at a deli counter

7. Inter Process Communication IPC for short One example is the synchronous filter mechanism – think of the unix pipe One process writes to the pipe until it is full Unidirectional and bound to source and target Not secure Can also used a Named Pipe

8. Files Files can be used for process communication Can handle large volumes of data What kind of problems do you think you might run into to ?

9. Shared Memory Local processes can use shared memory area. No inherent means of synchronization so semaphores may be used Not suitable for large volumes of data Think of a ‘clipboard’

10. Message Queues Process can read and write to a named queue Synchronization is built in Only suitable for small amounts of data

11. Structuring a distributed system Master-slave Client/server Peer-to-peer Group Distributed object Multimedia stream

12. Samples http://www.cs.cf.ac.uk/Dave/C/