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Chapter 4: Threads Operating System Concepts – 8th Edition Silberschatz, Galvin and Gagne ©2009 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 Operating System Concepts – 8th Edition 4.2 Silberschatz, Galvin and Gagne ©2009 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 Operating System Concepts – 8th Edition 4.3 Silberschatz, Galvin and Gagne ©2009 Single and Multithreaded Processes Operating System Concepts – 8th Edition 4.4 Silberschatz, Galvin and Gagne ©2009 Recall a process’s address space 0xFFFFFFFF stack (dynamic allocated mem) SP heap (dynamic allocated mem) static data (data segment) 0x00000000 Operating System Concepts – 8th Edition code (text segment) 4.5 PC Silberschatz, Galvin and Gagne ©2009 A process’s address space with threads thread 1 stack 0xFFFFFFFF SP thread 2 stack thread 3 stack SP (T1) SP (T2) SP (T3) address space heap (dynamic allocated mem) static data (data segment) 0x00000000 Operating System Concepts – 8th Edition PC code (text segment) 4.6 PC (T2) PC (T1) PC (T3) Silberschatz, Galvin and Gagne ©2009 Benefits Responsiveness Resource Sharing Economy Scalability Operating System Concepts – 8th Edition 4.7 Silberschatz, Galvin and Gagne ©2009 Multithreaded Server Architecture Operating System Concepts – 8th Edition 4.8 Silberschatz, Galvin and Gagne ©2009 Concurrent Execution on a Single-core System Operating System Concepts – 8th Edition 4.9 Silberschatz, Galvin and Gagne ©2009 Parallel Execution on a Multicore System Operating System Concepts – 8th Edition 4.10 Silberschatz, Galvin and Gagne ©2009 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 Operating System Concepts – 8th Edition 4.11 Silberschatz, Galvin and Gagne ©2009 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 Operating System Concepts – 8th Edition 4.12 Silberschatz, Galvin and Gagne ©2009 Multithreading Models Many-to-One One-to-One Many-to-Many Operating System Concepts – 8th Edition 4.13 Silberschatz, Galvin and Gagne ©2009 Many-to-One Many user-level threads mapped to single kernel thread Examples: Solaris Green Threads GNU Portable Threads Operating System Concepts – 8th Edition 4.14 Silberschatz, Galvin and Gagne ©2009 Many-to-One Model Operating System Concepts – 8th Edition 4.15 Silberschatz, Galvin and Gagne ©2009 One-to-One Each user-level thread maps to kernel thread Examples Windows NT/XP/2000 Linux Solaris 9 and later Operating System Concepts – 8th Edition 4.16 Silberschatz, Galvin and Gagne ©2009 One-to-one Model Operating System Concepts – 8th Edition 4.17 Silberschatz, Galvin and Gagne ©2009 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 Operating System Concepts – 8th Edition 4.18 Silberschatz, Galvin and Gagne ©2009 Many-to-Many Model Operating System Concepts – 8th Edition 4.19 Silberschatz, Galvin and Gagne ©2009 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 Operating System Concepts – 8th Edition 4.20 Silberschatz, Galvin and Gagne ©2009 Two-level Model Operating System Concepts – 8th Edition 4.21 Silberschatz, Galvin and Gagne ©2009 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 Operating System Concepts – 8th Edition 4.22 Silberschatz, Galvin and Gagne ©2009 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) Operating System Concepts – 8th Edition 4.23 Silberschatz, Galvin and Gagne ©2009 Pthreads Example Operating System Concepts – 8th Edition 4.24 Silberschatz, Galvin and Gagne ©2009 Pthreads Example (Cont.) Operating System Concepts – 8th Edition 4.25 Silberschatz, Galvin and Gagne ©2009 Win32 API Multithreaded C Program Operating System Concepts – 8th Edition 4.26 Silberschatz, Galvin and Gagne ©2009 Win32 API Multithreaded C Program (Cont.) Operating System Concepts – 8th Edition 4.27 Silberschatz, Galvin and Gagne ©2009 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 Operating System Concepts – 8th Edition 4.28 Silberschatz, Galvin and Gagne ©2009 Java Multithreaded Program Operating System Concepts – 8th Edition 4.29 Silberschatz, Galvin and Gagne ©2009 Java Multithreaded Program (Cont.) Operating System Concepts – 8th Edition 4.30 Silberschatz, Galvin and Gagne ©2009 Semantics of fork() and exec() Does fork() duplicate only the calling thread or all threads? Operating System Concepts – 8th Edition 4.31 Silberschatz, Galvin and Gagne ©2009 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. Operating System Concepts – 8th Edition 4.32 Silberschatz, Galvin and Gagne ©2009 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 Operating System Concepts – 8th Edition 4.33 Silberschatz, Galvin and Gagne ©2009 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 Operating System Concepts – 8th Edition 4.34 Silberschatz, Galvin and Gagne ©2009 Lightweight Processes Operating System Concepts – 8th Edition 4.35 Silberschatz, Galvin and Gagne ©2009 End of Chapter 4 Operating System Concepts – 8th Edition Silberschatz, Galvin and Gagne ©2009