Figure 5.01

Figure 5.01

Chapter 4: Threads Operating System Concepts 8th Edition Silberschatz, Galvin and Gagne 2009 Chapter 4: Threads Overview Multithreading Models Thread Libraries

Threading Issues Operating System Examples Windows XP Threads Linux Threads Operating System Concepts 8th Edition 4.2

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

4.3 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 4.4 Silberschatz, Galvin and Gagne 2009 Single and Multithreaded Processes Operating System Concepts 8th Edition 4.5 Silberschatz, Galvin and Gagne 2009 Benefits

Responsiveness Resource Sharing Economy Scalability Operating System Concepts 8th Edition 4.6 Silberschatz, Galvin and Gagne 2009

Multicore Programming Multicore systems putting pressure on programmers, challenges include: Dividing activities Balance Data splitting

Data dependency Testing and debugging 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 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 Examples Windows XP/2000

Solaris Linux Tru64 UNIX Mac OS X 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 Threading Issues Semantics of fork() and exec() system calls Thread cancellation of target thread

Asynchronous or deferred Signal handling Synchronous and asynchronous Operating System Concepts 8th Edition 4.31 Silberschatz, Galvin and Gagne 2009 Threading Issues (Cont.) Thread pools

Thread-specific data Create Facility needed for data private to thread Scheduler activations Operating System Concepts 8th Edition 4.32 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 4.33 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 4.34 Silberschatz, Galvin and Gagne 2009 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 1. Signal is generated by particular event 2. Signal is delivered to a process 3. 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 Operating System Concepts 8th Edition 4.35 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

4.36 Silberschatz, Galvin and Gagne 2009 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) Operating System Concepts 8th Edition 4.37 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 4.38

Silberschatz, Galvin and Gagne 2009 Lightweight Processes Operating System Concepts 8th Edition 4.39 Silberschatz, Galvin and Gagne 2009 Operating System Examples Windows XP Threads Linux Thread

Operating System Concepts 8th Edition 4.40 Silberschatz, Galvin and Gagne 2009 Windows XP Threads Data Structures Operating System Concepts 8th Edition 4.41 Silberschatz, Galvin and Gagne 2009 Windows XP Threads Implements the one-to-one mapping, kernel-level

Each thread contains A thread id Register set Separate user and kernel stacks 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)

Operating System Concepts 8th Edition 4.42 Silberschatz, Galvin and Gagne 2009 Linux Threads Linux refers to them as tasks rather than threads Thread creation is done through clone() system call clone() allows a child task to share the address space of the parent task (process)

struct task_struct points to process data structures (shared or unique) Operating System Concepts 8th Edition 4.43 Silberschatz, Galvin and Gagne 2009 Linux Threads fork() and clone() system calls Doesnt distinguish between process and thread

Uses term task rather than thread clone() takes options to determine sharing on process create struct task_struct points to process data structures (shared or unique) Operating System Concepts 8th Edition 4.44 Silberschatz, Galvin and Gagne 2009 End of Chapter 4 Operating System Concepts 8th Edition Silberschatz, Galvin and Gagne 2009

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