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Chapter 4: Threads

Chapter 4: Threads. Single and Multithreaded Processes. Benefits. Responsiveness One part of a program can continue running even if another part is blocked Resource Sharing Threads of the same process share the same memory space and resources. Economy

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Chapter 4: Threads

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  1. Chapter 4: Threads

  2. Single and Multithreaded Processes

  3. Benefits • Responsiveness • One part of a program can continue running even if another part is blocked • Resource Sharing • Threads of the same process share the same memory space and resources. • Economy • Much less time consuming to create and manage threads than processes • Solaris 2: creating a process is 30 times slower than creating a thread, context switching is 5 times slower. • Scalability • Each thread can run in parallel on a different processor

  4. Example of Use • Multithreaded Server (for instance a Web Server)

  5. Multicore Programming & Multithreading • Multicore systems putting pressure on programmers, challenges include • Dividing activities • Balance • Data splitting • Data dependency • Testing and debugging

  6. Concurrent Execution on a Single-core System

  7. Parallel Execution on a Multicore System

  8. User Threads • User threads supported above the kernel and managed without kernel support • Thread management done by user-level threads library • Three primary thread libraries: • POSIX Pthreads • Win32 threads • Java threads

  9. Kernel Threads • Supported by the Kernel • Examples • Windows XP/2000 • Solaris • Linux • Tru64 UNIX • Mac OS X

  10. Multithreading Models • Many-to-One • One-to-One • Many-to-Many

  11. Many-to-One • Many user-level threads mapped to single kernel thread • Entire process blocks with a thread blocking system call • Examples: • Solaris Green Threads • GNU Portable Threads

  12. One-to-One • Each user-level thread maps to kernel thread • Creation of a user thread requires creation of a kernel thread • Examples • Windows NT/XP/2000 • Linux • Solaris 9 and later

  13. Many-to-Many Model • Allows many user level threads to be mapped to many kernel threads (smaller or equal number) • Allows the operating system to create a sufficient number of kernel threads • Solaris prior to version 9 • Windows NT/2000 with the ThreadFiber package

  14. Many-to-Many Model

  15. Two-level Model • Similar to M:M, except that it also allows a user thread to be bound to kernel thread • Examples • IRIX • HP-UX • Tru64 UNIX • Solaris 8 and earlier

  16. Two-level Model

  17. 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

  18. Pthreads • Refers to the POSIX standard (IEEE 1003.1c) API for thread creation and synchronization • May be provided either as user-level or kernel-level • POSIX standard specifies behavior of the thread library; Implementation is up to development of the library • Common in UNIX operating systems (Solaris, Linux, Mac OS X)

  19. Win32 Threads • Also known as Windows API or WinAPI • Win32 is a kernel-level library • Available on Windows systems (Windows 95, 98, NT, 2000 and XP)

  20. Windows XP Threads • Implements the one-to-one mapping, kernel-level • Each thread contains • A thread id • Register set • user stack or kernel stack • Private data storage area • The register set, stacks, and private storage area are known as the context of the threads • The primary data structures of a thread include: • ETHREAD (executive thread block) • KTHREAD (kernel thread block) • TEB (thread environment block)

  21. Windows XP Threads

  22. Linux Threads • Linux refers to them as tasks rather than threads • Thread creation is done through clone() system call • Flags, arguments of clone() specify sharing details

  23. Linux Threads • If CLONE_FS, CLONE_VM, CLONE_SIGHAND, and CLONE_FILES are passed to clone(), parent and child tasks share every thing • If none of these flags are passed to clone(), no sharing takes place, resulting in functionality similar to that of fork()

  24. End of Chapter 4

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