1. Silberschatz, Galvin and Gagne ©2009Operating System Concepts – 8 th Edition Chapter 4: Threads

2. 4.2 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Objectives To introduce the notion of a thread — a fundamental unit of CPU utilization that forms the basis of multithreaded computer systems To discuss the APIs for the Pthreads, Win32, and Java thread libraries To examine issues related to multithreaded programming

3. 4.3 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Motivation Threads run within application Multiple tasks with the application can be implemented by separate threads Update display Fetch data Spell checking Answer a network request Process creation is heavy-weight while thread creation is light-weight Can simplify code, increase efficiency Kernels are generally multithreaded

4. 4.4 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Single and Multithreaded Processes

5. 4.5 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Recall a process’s address space 0x00000000 0xFFFFFFFF code (text segment) static data (data segment) heap (dynamic allocated mem) stack (dynamic allocated mem) PC SP

6. 4.6 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition A process’s address space with threads 0x00000000 0xFFFFFFFF address space code (text segment) static data (data segment) heap (dynamic allocated mem) thread 1 stack PC (T2) SP (T2) thread 2 stack thread 3 stack SP (T1) SP (T3) PC (T1) PC (T3) SP PC

7. 4.7 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Benefits Responsiveness Resource Sharing Economy Scalability

8. 4.8 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Multithreaded Server Architecture

9. 4.9 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Concurrent Execution on a Single-core System

10. 4.10 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Parallel Execution on a Multicore System

11. 4.11 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition User Threads Thread management done by user-level threads library: the user-level process (user-level threads) a library linked into the program manages the threads. To make threads cheap and fast, they need to be implemented at the user level managed entirely by user-level library, e.g. libpthreads.a each process keeps track of its own threads in a thread table Three primary thread libraries: POSIX Pthreads Win32 threads Java threads

12. 4.12 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Kernel Threads Supported by the Kernel all thread operations are implemented in the kernel OS schedules all of the threads in a system if one thread in a process blocks (e.g. on I/O), the OS knows about it, and can run other threads from that process possible to overlap I/O and computation inside a process

13. 4.13 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Multithreading Models Many-to-One One-to-One Many-to-Many

14. 4.14 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Many-to-One Many user-level threads mapped to single kernel thread Examples: Solaris Green Threads GNU Portable Threads

15. 4.15 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Many-to-One Model

16. 4.16 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition One-to-One Each user-level thread maps to kernel thread Examples Windows NT/XP/2000 Linux Solaris 9 and later

17. 4.17 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition One-to-one Model

18. 4.18 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Many-to-Many Model Allows many user level threads to be mapped to many kernel threads Allows the operating system to create a sufficient number of kernel threads Solaris prior to version 9 Windows NT/2000 with the ThreadFiber package

19. 4.19 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Many-to-Many Model

20. 4.20 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Two-level Model Similar to M:M, except that it allows a user thread to be bound to kernel thread Examples IRIX HP-UX Tru64 UNIX Solaris 8 and earlier

21. 4.21 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Two-level Model

22. 4.22 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Thread Libraries Thread library provides programmer with API for creating and managing threads Two primary ways of implementing Library entirely in user space Kernel-level library supported by the OS

23. 4.23 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Pthreads May be provided either as user-level or kernel-level A POSIX standard (IEEE 1003.1c) API for thread creation and synchronization API specifies behavior of the thread library, implementation is up to development of the library Common in UNIX operating systems (Solaris, Linux, Mac OS X)

24. 4.24 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Pthreads Example

25. 4.25 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Pthreads Example (Cont.)

26. 4.26 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Win32 API Multithreaded C Program

27. 4.27 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Win32 API Multithreaded C Program (Cont.)

28. 4.28 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Java Threads Java threads are managed by the JVM Typically implemented using the threads model provided by underlying OS Java threads may be created by: Extending Thread class Implementing the Runnable interface

29. 4.29 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Java Multithreaded Program

30. 4.30 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Java Multithreaded Program (Cont.)

31. 4.31 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Semantics of fork() and exec() Does fork() duplicate only the calling thread or all threads?

32. 4.32 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Thread Cancellation Terminating a thread before it has finished Two general approaches: Asynchronous cancellation terminates the target thread immediately. Deferred cancellation allows the target thread to periodically check if it should be cancelled.

33. 4.33 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Thread Pools Create a number of threads in a pool where they await work Advantages: Usually slightly faster to service a request with an existing thread than create a new thread Allows the number of threads in the application(s) to be bound to the size of the pool

34. 4.34 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Scheduler Activations Both M:M and Two-level models require communication to maintain the appropriate number of kernel threads allocated to the application Scheduler activations provide upcalls - a communication mechanism from the kernel to the thread library This communication allows an application to maintain the correct number kernel threads

35. 4.35 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Lightweight Processes

36. Silberschatz, Galvin and Gagne ©2009Operating System Concepts – 8 th Edition End of Chapter 4