Chapter 4: Multithreaded Programming Dr. Varin Chouvatut. Operating System Concepts 8 th Edition,

Transcription

1 Chapter 4: Multithreaded Programming Dr. Varin Chouvatut, Silberschatz, Galvin and Gagne 2010

2 Chapter 4: Multithreaded Programming Overview Multithreading Models Thread Libraries Threading Issues Operating System Examples Windows XP Threads Linux Threads 4.2 Silberschatz, Galvin and Gagne 2010

3 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 basis : รากฐาน, ฐานหล ก 4.3 Silberschatz, Galvin and Gagne 2010

4 In Chapter 3 assumed a process was an executing program with a single thread of control sometime called Heavyweight process (HWP) A Thread is a basic unit of CPU utilization Each Thread is composed of - thread ID - program counter - register set - stack A thread shares with other threads belonging to the same process its code section, data section, and other OS resources, such as open files and signals. * If the process has multiple threads of control, it can do more than one task at a time. 4.4 Silberschatz, Galvin and Gagne 2010

5 Single and Multithreaded Processes HWP LWP Ex. Web server using run on single-threaded process, it would be able to service only one client at a time. Ex. Word Processor using run on multithreaded processes: thread for displaying graphics, thread for reading keystrokes from user and thread for spelling and grammar checking. 4.5 Silberschatz, Galvin and Gagne 2010

6 Benefits ข อได เปร ยบของ Multithreaded programming แบ งได เป น 4 Categories : Responsiveness EX. A multithreaded web browser could allow user interaction in one thread while an image was being loaded in another thread. Resource Sharing Threads share memory & resources of the process to which they belong; it allows an application to have several different threads of activity within the same address space. Economy Because threads share resources of the process; it is more economical to create and context-switch threads. It is much more time consuming to create and manage processes than threads. Scalability The benefits of multithreading can be greatly increased in a multiprocessor architecture, where threads may be running in parallel on different processors. 4.6 Silberschatz, Galvin and Gagne 2010

7 Multithreaded Server Architecture Example of Web server listening for many client request 4.7 Silberschatz, Galvin and Gagne 2010

8 Multicore Programming Multicore systems have placed pressure on programmers, challenges in programming include Dividing activities Balance Data splitting Data dependency Testing and debugging 4.8 Silberschatz, Galvin and Gagne 2010

9 Concurrent Execution on a Single-core System 4.9 Silberschatz, Galvin and Gagne 2010

10 Parallel Execution on a Multicore System 4.10 Silberschatz, Galvin and Gagne 2010

11 User Threads Support for threads is provided at the user level. User threads are supported above the kernel and are managed without kernel support. Thread management is done by the thread library (of user-level) in user space. Library supports for thread creation, scheduling & management with no support from the kernel. Fast to create and manage Three primary thread libraries in use today: POSIX Pthreads Win32 Threads Java Threads 4.11 Silberschatz, Galvin and Gagne 2010

12 Kernel Threads Support for threads is provided by the Kernel. Thread creation, scheduling & management is done by the kernel-level library in kernel space. Kernel threads are supported and managed directly by the OS; the kernel threads are generally slower to create and manage than user threads. In a multiprocessor environment, the kernel can schedule threads on different processors. Examples of contemporary OS s which support kernel threads: Windows XP/2000 Solaris Linux Tru64 UNIX (formerly Digital UNIX) Mac OS X 4.12 Silberschatz, Galvin and Gagne 2010

13 Multithreading Models Many systems provide support for both user and kernel threads. Many-to-One Model 3 common types of multithreading models : One-to-One Model Many-to-Many Model 4.13 Silberschatz, Galvin and Gagne 2010

14 Many-to-One Many user-level threads are mapped to a single kernel thread Examples: Solaris s Green Threads GNU Portable Threads 4.14 Silberschatz, Galvin and Gagne 2010

15 Many-to-One Model - Only one thread can access the kernel at a time 4.15 Silberschatz, Galvin and Gagne 2010

16 One-to-One Each user thread are mapped to a kernel thread Provide more concurrency than the many-to-one model by allowing another thread to run when a thread makes a blocking system call. Allow multiple threads to run in parallel on multiprocessors Examples Windows NT/XP/2000 Linux Solaris 9 and later 4.16 Silberschatz, Galvin and Gagne 2010

17 One-to-one Model 4.17 Silberschatz, Galvin and Gagne 2010

18 Many-to-Many Model Allows many user-level threads to be multiplexed to a smaller or equal number of 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 4.18 Silberschatz, Galvin and Gagne 2010

19 Many-to-Many Model 4.19 Silberschatz, Galvin and Gagne 2010

20 Two-level Model Similar to M:M, except that it also allows a user thread to be bound to a kernel thread Examples of OS s support the two-level model: IRIX HP-UX Tru64 UNIX Solaris 8 and earlier M:M ค อ Many-to-Many model 4.20 Silberschatz, Galvin and Gagne 2010

21 Two-level Model 4.21 Silberschatz, Galvin and Gagne 2010

22 Thread Libraries Thread library provides programmer with an API for creating and managing threads Two primary ways of implementing a thread library: A library entirely in user space with no kernel support. A kernel-level library supported by the OS. As mentioned, three main thread libraries are in use today are POSIX Pthreads Win32 Java 4.22 Silberschatz, Galvin and Gagne 2010

23 Pthreads May be provided as either a user-level or a kernel-level library Pthreads refers to the POSIX standard (IEEE c) defining an 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, Tru64 UNIX) 4.23 Silberschatz, Galvin and Gagne 2010

24 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 the Thread class Implementing the Runnable interface 4.24 Silberschatz, Galvin and Gagne 2010

25 Threading Issues Semantics of fork() and exec() system calls Thread cancellation of target thread Asynchronous or deferred Signal handling Thread pools Thread-specific data Scheduler activations 4.25 Silberschatz, Galvin and Gagne 2010

26 Semantics of fork() and exec() Does fork() (or exec()) duplicate only the calling thread or all threads in a multithreaded program? 4.26 Silberschatz, Galvin and Gagne 2010

27 Thread Cancellation Terminating a thread before it has finished A thread that is to be canceled is often referred to as the target thread. Two general approaches: Asynchronous cancellation terminates the target thread immediately 1 thread terminates the target thread Deferred cancellation allows the target thread to periodically check if it should be cancelled target thread can periodically check if it should terminate the thread can terminate itself in an orderly fashion immediately: ท นท ท นใด 4.27 Silberschatz, Galvin and Gagne 2010

28 Signal Handling Signals are used in UNIX systems to notify a process that a particular event has occurred A signal handler is used to handle the signals 1. Signal is generated by the occurrence of a particular event 2. Signal is delivered to a process (after it is generated) 3. Signal must be handled, once it is delivered Options of signal delivery in multithreaded programs: 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 4.28 Silberschatz, Galvin and Gagne 2010

29 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 to create a new thread Allows the limited number of threads in the application(s) to be bound to the size of the pool 4.29 Silberschatz, Galvin and Gagne 2010

30 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) 4.30 Silberschatz, Galvin and Gagne 2010

31 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 upcall(s) - a communication mechanism from the kernel to the user-thread library For kernel to inform an application about certain events. This communication allows an application to maintain the correct number kernel threads 4.31 Silberschatz, Galvin and Gagne 2010

32 Operating-System Examples Windows XP Threads Linux Thread 4.32 Silberschatz, Galvin and Gagne 2010

33 Windows XP Threads Windows XP implements the one-to-one mapping, kernel-level library (Win32 API) Each thread contains A thread ID A register set A user stack and a kernel stack A private 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) 4.33 Silberschatz, Galvin and Gagne 2010

34 Windows XP Threads 4.34 Silberschatz, Galvin and Gagne 2010

35 Linux Threads Linux refers to the term task(s) rather than thread(s) when referring to a flow of control within a program Thread creation is done through clone() system call clone() allows a child task to share the address space of the parent task (process) 4.35 Silberschatz, Galvin and Gagne 2010

36 Linux Threads 4.36 Silberschatz, Galvin and Gagne 2010

37 End of Chapter 4, Silberschatz, Galvin and Gagne 2010