1. 1 Threads, SMP, and Microkernels Chapter 4

2. 2 Process: Some Info. Motivation for threads! Two fundamental aspects of a “process”: Resource ownership Scheduling or execution Resource ownership - process includes a virtual address space to hold the process image Scheduling/execution- follows an execution path that may be interleaved with other processes These two characteristics are treated independently by the operating system

3. 3 Process Dispatching is referred to as a thread or lightweight process Resource of ownership is referred to as a process or task So far, we have considered processes that had just one thread: A “process” or a “process with one thread” are kind of similar!

4. 4 Multithreading An attempt to define multithreading: Operating system supports multiple threads of execution within a single process MS-DOS supports a single thread UNIX supports multiple user processes but only supports one thread per process Windows, Solaris, Linux, Mach, and OS/2 support multiple threads

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6. 6 What exactly is a Process now? Have a virtual address space which holds the process image Protected access to processors, other processes, files, and I/O resources

7. 7 What exactly is a Thread now? An execution state (running, ready, etc.) 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

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9. 9 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

10. 10 Uses of Threads in a Single-User Multiprocessing System Foreground to background work: In GUI-based applications, one thread can make display and the other can process input Asynchronous processing: Daemons or services in OSes Speed of execution: Make even better use of processor, especially in multiprocessor systems Modular program structure

11. 11 Threads: What happens to state models? 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

12. 12 Thread States States associated with a change in thread state Spawn Spawn another thread Block Unblock Finish Deallocate register context and stacks

13. 13 Remote Procedure Call Using Single Thread

14. 14 Remote Procedure Call Using Threads

15. 15 Multithreading

16. 16 TOP Command

17. 17 PSTREE Command

18. 18 /proc directory on Linux

19. 19 Details of Process 2114

20. 20 Adobe PageMaker

21. 21 Categories of Thread Implementation User-level threads Kernel-level threads

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23. 23 User-Level Threads All thread management is done by the application The kernel is not aware of the existence of threads

24. 24 User-Level Threads

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26. 26 Kernel-Level Threads Windows is an example of this approach Kernel maintains context information for the process and the threads Scheduling is done on a thread basis

27. 27 Kernel-Level Threads

28. 28 VAX Running UNIX-Like Operating System

29. 29 Combined Approaches Example is Solaris Thread creation done in the user space Bulk of scheduling and synchronization of threads within application

30. 30 Combined Approaches

31. 31 Relationship Between Threads and Processes

32. 32 Flynn’s Taxonomy There is no authoritative classification of parallel computers! Flynn’s taxonomy is one such classification based on number of instruction and data stream processed by a parallel computer: Single Instruction Single Data (SISD) Multiple Instruction Single Data (MISD) Single Instruction Multiple Data (SIMD) Multiple Instruction Multiple Data (MIMD) Almost all modern computers fall in this category

33. 33 Flynn’s Taxonomy Extensions to Flynn’s taxonomy: Single Program Multiple Data (SPMD)—a programming model This classification is largely outdated!

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35. 35 Symmetric Multi-Processors (SMP) A SMP is a parallel processing system with a shared-everything approach: The term signifies that each processor shares the main memory and possibly the cache Typically a SMP can have 2 to 256 processors Examples include AMD Athlon, AMD Opteron 200 and 2000 series, Intel XEON etc

36. 36 Shared Memory All processors have access to shared memory: Notion of “Global Address Space”

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38. 38 Multiprocessor Operating System Design Considerations Simultaneous concurrent processes or threads: Executing same kernel code should not result in erroneous behavior Scheduling: Opportunities exist to execute multiple threads of the same process Synchronization Memory management Reliability and fault tolerance

39. 39 Microkernels Small operating system core Contains only essential core operating systems functions Many services traditionally included in the operating system are now external subsystems Device drivers File systems Virtual memory manager Windowing system Security services

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41. 41 Benefits of a Microkernel Organization Uniform interface on request made by a process Extensibility Flexibility Portability Reliability Distributed System Support Object-oriented Operating System

42. 42 Microkernel Design Low-level memory management Mapping each virtual page to a physical page frame

43. 43 Microkernel Design Interprocess communication I/O and interrupt management