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Chapter 4 Multithreaded Programming

Chapter 4 Multithreaded Programming. Objectives To introduce a notion of a thread – a fundamental unit of CPU utilization that forms the basis of multithreaded computer systems To discuss the APIs for thread libraries (skip) To examine issues related to multithreaded programming.

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Chapter 4 Multithreaded Programming

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  1. Chapter 4 Multithreaded Programming Objectives To introduce a notion of a thread – a fundamental unit of CPU utilization that forms the basis of multithreaded computer systems To discuss the APIs for thread libraries (skip) To examine issues related to multithreaded programming

  2. Chapter 4: Multithreaded Programming • Overview • Multithreading Models • Thread Library (skip) • Threading Issues • Linux Threads (skip)

  3. 4.1 Overview Single and Multithreaded Processes

  4. Multithreaded Server Architecture

  5. Benefits • Responsiveness: • Allow an interactive program to continue running even if part of it is blocked or is performing a lengthy operation • Resource Sharing • Threads share the memory and the resources of the process • Economy • It is more economical to create and context-switch threads. For example, in Solaris, creating a process is 30 times slower than creating a thread, and context switching a process is 5 times slower than context switching a thread • Scalability • Utilization of Multiprocessor Architectures • Threads may be running in parallel on different processors

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

  7. 4.2 Multithreading Models How to establish the relationship between user and kernel threads Many-to-One One-to-One Many-to-Many • User Threads • Thread management done by user-level threads library • Three primary thread libraries: • POSIX Pthreads, Win32 threads, Java threads • Kernel threads • Supported by the kernel (operating system) • Examples： • Windows XP/2000, Solaris, Linux, Tru64 UNIX, Mac OS X

  8. Many-to-One Many user-level threads mapped to single kernel thread Examples: Solaris Green Threads, GNU Portable Threads Thread management is done in user space, so it is efficient. If a thread makes a blocking system call, then the entire process will block

  9. One-to-One Each user-level thread maps to kernel thread Examples Windows NT/XP/2000, Linux, Solaris 9 and later Drawback: creating a user thread requires creating the corresponding kernel thread Restrict the number of threads supported by the system

  10. 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 Examples: Solaris prior to version 9, Windows NT/2000 with the ThreadFiber package

  11. Two-level Model Similar to Many-to-Many, except that it allows a user thread to be bound to kernel thread Examples IRIX, HP-UX, Tru64 UNIX, Solaris 8 and earlier Skip 4.3

  12. 4.4 Threading Issues (1) • Semantics of fork( ) and exec( ) system calls • Does fork( ) duplicate only the calling thread or all threads? • Thread cancellation of target thread • 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

  13. Threading Issues (2) • Signal Handling • Signals are used in UNIX systems to notify a process that a particular event has occurred • A signal handler is used to process signals • Signal is generated by particular event • Signal is delivered to a process • Signal is handled • Options: • Deliver the signal to the thread to which the signal applies • Deliver the signal to every thread in the process • Deliver the signal to certain threads in the process • Assign a specific thread to receive all signals for the process

  14. Threading Issues (3) • 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 Skip p.169 這 2 點以下的部分

  15. Threading Issues (4) • Thread Specific Data • Allows each thread to have its own copy of data • Useful when you do not have control over the thread creation process (i.e., when using a thread pool) • 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 • Handled by an upcall handler running on a virtual processor • This communication allows an application to maintain the correct number kernel threads Skip 4.5, 4.6

  16. Light Weight Process

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