1. Threads, SMP and Microkernels Process vs. thread: –Unit of resource ownership (process has virtual address space, memory, I/O channels, files) –Unit of dispatching process execution path through one or more programs process has execution state, process is dispatched.

2. Process/Threads Unit of dispatching=thread/lightweight process Unit of resource ownership: process/task

3. Multithreading Support multiple threads execution within one process (one process, one thread is single threading) Within a process, have >1 thread. Thread has (a) thread execution state, (b) saved thread context, © execution context, (d) per-thread storage

4. Multithreading; continued All threads of a process –share state and resources of that process –reside in same address space and have same access –one thread alters data=> others see change –one thread opens file=> other threads have access

5. Benefits of multithreading Performance: –far less time to create, terminate and switch between threads –factor of 10 improvement in performance –example: server –>1 CPU? –IPC more time consuming

6. Thread operations Spawn (first thread created automatically) Block waiting for an event Unblock -- event occurs finish-- thread completes

7. Thread implementations User level threads (ULT) Kernel level threads (KLT) Combined approach

8. MS-DOS One process One thread

9. Many UNIX OS Multiple processes One thread/process Process 1 Process 2

10. Java Runtime Environment One process; Multipe threads

11. Solaris Multiple processes; multiple threads We are interested in this

12. Multithreading Process = unit of protection + unit of resource allocation has virtual address space; protected access to processor, other processes (IPC), files,, I/O resources… Within a process, have more than one thread.

13. Symmetric MultiProcessing SIMD MIMD –Distributed memory –Shared memory master/slave Symmetric (each process self schedules)

14. Microkernels Small OS core; provides foundation for modular extension Benefits: –uniform interfaces –extensibility –flexibility –portability –Distributed OS support