Chapter 4: Threads

4.2 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th edition, Jan 23, 2005 Chapter 4: Threads Overview Multithreading Models Threading Issues Pthreads Windows XP Threads Linux Threads Java Threads

4.3 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th edition, Jan 23, 2005 Thread: Definition A Thread is a basic unit of CPU utilization. A thread of execution. A placeholder information associated with a single use of a program that can handle multiple concurrent users Thread Lightweight process (LWP) Threads of instructions or thread of control Shares address space and other global information with its process Registers, stack, signal masks and other thread-specific data are local to each thread

4.4 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th edition, Jan 23, 2005 Thread Composition A Thread is comprised of: A thread ID. A program counter. A register set. A stack.

4.5 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th edition, Jan 23, 2005 Process vs Threads A traditional or heavyweight process has a single thread of control. If a process has multiple threads of control, it can perform more than one task at a time, thus a thread is a lightweight process.

4.6 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th edition, Jan 23, 2005 Single and Multithreaded Processes

4.7 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th edition, Jan 23, 2005 Benefits Responsiveness A program may continue even if parts of it are blocked. Ex: web browser loading some images while others take more time. Resource Sharing By default, threads share memory and the resources of the process to which they belong. Economy Easier to create and context switch between threads since they share resources. Utilization of MP Architectures Run multiple threads in parallel, taking advantage of multiple processors.

4.8 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th edition, Jan 23, 2005 Benefits Takes less time to create a new thread than a process. Less time to terminate a thread than a process. Less time to switch between two threads within the same process. Since threads within the same process share memory and files, they can communicate with each other without invoking the kernel

4.9 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th edition, Jan 23, 2005 Multithreading Modes Provided in different levels: User Threads.  Supported above the kernel and managed without kernel support. Kernel Threads.  Supported and managed directly by the operating system.

4.10 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th edition, Jan 23, 2005 User Threads Thread management done by user-level threads library. The kernel is not aware of the existence of threads. Three primary thread libraries: POSIX Pthreads Win32 threads Java threads

4.11 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th edition, Jan 23, 2005 Kernel Threads Supported by the Kernel Kernel maintains context information for the process and the threads Examples Windows XP/2000 Solaris Linux Tru64 UNIX Mac OS X

4.12 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th edition, Jan 23, 2005 Multithreading Models Many-to-One Maps many user-level threads to a single kernel thread. One-to-One Maps each user-level thread to a kernel thread. Many-to-Many Multiplexes many user-level threads to a smaller or equal number of kernel threads.

4.13 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th edition, Jan 23, 2005 Many-to-One Many user-level threads mapped to single kernel thread. Thread management is done by the thread library in user space. Will block if thread makes a blocking system call. Multiple threads are unable to run in parallel on multiprocessors. Examples: Solaris Green Threads GNU Portable Threads

4.14 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th edition, Jan 23, 2005 Many-to-One Model

4.15 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th edition, Jan 23, 2005 One-to-One Each user-level thread maps to kernel thread. Provides more concurrency allowing another thread to run when one makes a blocking system call. Allows multiple threads to run in parallel in multiprocessors. Developer must be careful not to make too many threads per application. Examples Windows NT/XP/2000 Linux Solaris 9 and later

4.16 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th edition, Jan 23, 2005 One-to-one Model

4.17 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th edition, Jan 23, 2005 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. Developers can create as many threads as necessary. Solaris prior to version 9. Windows NT/2000 with the ThreadFiber package.

4.18 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th edition, Jan 23, 2005 Many-to-Many Model

4.19 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th edition, Jan 23, 2005 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

4.20 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th edition, Jan 23, 2005 Two-level Model

4.21 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th edition, Jan 23, 2005 Thread State: Life Cycle of a Thread Thread states Born state Ready state (runnable state) Running state Dead state Blocked state Waiting state Sleeping state  Sleep interval specifies for how long a thread will sleep

4.22 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th edition, Jan 23, 2005 Thread State: Life Cycle of a Thread Thread Life Cycle:

4.23 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th edition, Jan 23, 2005 Thread Libraries A thread library provides the programmer an API for creating and mapping threads. Two ways of implementing a thread library: Library entirely in user space with no kernel support.  Invoking a function in the library results in a local call function not a system call. Kernel-level library supported directly by the operating system.  Code and structures reside in kernel space.  Invoking a function in the API typically results in a system call to the kernel.

4.24 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th edition, Jan 23, 2005 Thread Libraries Three main libraries are used today: POSIX Pthreads.  User or kernel level. Win32.  Kernel level only on windows systems. Java.  Java programs.

4.25 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th edition, Jan 23, 2005 Pthreads A POSIX standard (IEEE c) 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) Third party support for Windows Systems.