1. Thread By Group III Kathryn Bean and Wafa’ Jaffal

2. Topics Covered Process vs. Thread Multithreading Benefits of Threads Thread States Different Thread Types Mapping between Processes and Threads Threading Issues Conclusion

3. Process vs. Thread, Process: Related to resource ownership Have a virtual address space which holds the process image Protected access to processors, other processes, files, and I/O resources

4. Process vs. Thread, Thread: Related to program execution Saved thread context when not running Has an execution stack Some per-thread static storage for local variables Access to the memory and resources of its process all threads of a process share this

5. Process vs. Thread Single-Threaded PCB Addr. Space Kernel Stack User Stack PCB Addr. Space Thread CB User Stack Kernel Stack Thread CB User Stack Kernel Stack Thread CB User Stack Kernel Stack Thread CB User Stack Kernel Stack Multithreaded

6. Multithreading MS-DOS - a single thread UNIX - multiple user processes but only supports one thread per process Java Run-Time engine - one process, multiple threads Windows 2000, Solaris, Linux, Mach, and OS/2 - multiple threads

7. Multithreading 1 Process 1 Thread M Processes 1 Thread per Process 1 Process M Threads M Processes N Threads

8. Benefits of Threads Takes less time to create a new thread than a process Less time to terminate a thread than a process Less time to switch between two threads within the same process Since threads within the same process share memory and files, they can communicate with each other without invoking the kernel

9. Uses of Threads Foreground to background work Asynchronous processing Speed execution Modular program structure

10. Remote Procedure Call Using Threads Server Time RPC Request RPC Using Single Thread Server

11. Remote Procedure Call Using Thread Server Time RPC Request Server RPC Request Thread 1 Thread 2

12. Threads within Process States Suspending a process involves suspending all threads of the process since all threads share the same address space Termination of a process, terminates all threads within the process

13. Thread States States associated with a change in thread state Spawn Spawn another thread Block Unblock Finish Deallocate register context and stacks

14. User-Level Threads (ULT) All thread management is done by the application The kernel is not aware of the existence of threads Example: POSIX Pthread Mach C-thread Solaris 2 UI-thread

15. Kernel-Level Threads (KLT) Kernel maintains context information for the process and the threads Scheduling is done on a thread basis W2K, Linux, and OS/2 are examples of this approach

16. Combined Approaches Example is Solaris Thread creation done in the user space Bulk of scheduling and synchronization of threads done in the user space Multiple ULT from a single application are mapped onto some number of KLT

18. Relationship Between Threads and Processes Threads:ProcessDescriptionExample Systems 1:1Each thread of execution is a unique process with its own address space and resources. Traditional UNIX implementations M:1 A process defines an address space and dynamic resource ownership. Multiple threads may be created and executed within that process. Windows NT, Solaris, OS/2, OS/390, MACH

19. Relationship Between Threads and Processes Threads:ProcessDescriptionExample Systems 1:MA thread may migrate from one process environment to another. This allows a thread to be easily moved among distinct systems. Ra (Clouds), Emerald M:MCombines attributes of M:1 and 1:M cases TRIX

20. Thread Issue Cancellation Target thread - thread to be cancelled Asynchronous cancellation Deferred cancellation Thread pool Create a number of threads at process startup and place them into a pool

21. Conclusion Responsiveness Resource sharing Economy Utilization of multiprocessor architectures Threads synchronization

22. Thank You Questions?

23. Bibliography W. Stallings, Operating Systems Prentice-Hall, 1998 A. Silberschatz, P. Galvin, G. Gagne, Operating System Concepts John Wiley & Sons, Inc. 2002