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Chapter 4: Threads

Chapter 4: Threads. 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.

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Chapter 4: Threads

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  1. Chapter 4: Threads

  2. 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. 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. Single and Multithreaded Processes

  5. Recall a process’s address space 0xFFFFFFFF stack (dynamic allocated mem) SP heap (dynamic allocated mem) static data (data segment) code (text segment) PC 0x00000000

  6. A process’s address space with threads thread 1 stack SP (T1) 0xFFFFFFFF thread 2 stack SP SP (T2) thread 3 stack SP (T3) address space heap (dynamic allocated mem) static data (data segment) 0x00000000 code (text segment) PC PC (T2) PC (T1) PC (T3)

  7. Benefits • Responsiveness • Resource Sharing • Economy • Scalability

  8. Multithreaded Server Architecture

  9. Concurrent Execution on a Single-core System

  10. Parallel Execution on a Multicore System

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

  14. Many-to-One • Many user-level threads mapped to single kernel thread • Examples: • Solaris Green Threads • GNU Portable Threads

  15. Many-to-One Model

  16. One-to-One • Each user-level thread maps to kernel thread • Examples • Windows NT/XP/2000 • Linux • Solaris 9 and later

  17. One-to-one Model

  18. 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. Many-to-Many Model

  20. 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. Two-level Model

  22. Thread Libraries • Thread libraryprovides 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. 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. Pthreads Example

  25. Pthreads Example (Cont.)

  26. Win32 API Multithreaded C Program

  27. Win32 API Multithreaded C Program (Cont.)

  28. 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. Java Multithreaded Program

  30. Java Multithreaded Program (Cont.)

  31. Semantics of fork() and exec() • Does fork() duplicate only the calling thread or all threads?

  32. 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. 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. 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. Lightweight Processes

  36. End of Chapter 4

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