Silberschatz, Galvin and Gagne  Operating System Concepts Chapter 5: Threads Overview Multithreading Models Threading Issues Pthreads Solaris 2 Threads Windows 2000 Threads Linux Threads Java Threads

Silberschatz, Galvin and Gagne  Operating System Concepts Process VS Thread Process has  Process environment – address space with code and data, open file handles, accounting info, other resources  Thread of control – program counter, register values, stack has execution history, current execution state Thread is a lightweight process  Has only the thread of control  Environment is shared with other threads in the same process

Silberschatz, Galvin and Gagne  Operating System Concepts Single and Multithreaded Processes

Silberschatz, Galvin and Gagne  Operating System Concepts Benefits Responsiveness  Multithreaded application can be more interactive Resource Sharing  Threads share resources Economy  Creating a process and allocating resources is costly – creating a thread is cheaper Utilization of Multi Processor Architectures  Many large computers have several CPUs

Silberschatz, Galvin and Gagne  Operating System Concepts User Threads Thread management done by user-level threads library  Thread creation and management is fast – no kernel involvement  No sophisticated scheduling  Can be implemented on an O.S. that doesn’t support threads Examples - POSIX Pthreads - Mach C-threads - Solaris threads

Silberschatz, Galvin and Gagne  Operating System Concepts Kernel Threads Supported by the Kernel  Slower to create and manage  Kernel provides scheduling and management  In a process with several threads, a page fault by one thread will not block entire process if other threads are runnable Examples - Windows 95/98/NT/ Solaris - Tru64 UNIX - BeOS - Linux

Silberschatz, Galvin and Gagne  Operating System Concepts Multithreading Models How to get the advantages of both user and kernel threads without the disadvantages of either:  Many-to-One  One-to-One  Many-to-Many

Silberschatz, Galvin and Gagne  Operating System Concepts Many-to-One Many user-level threads mapped to single kernel thread (process). Used on systems that do not support kernel threads.

Silberschatz, Galvin and Gagne  Operating System Concepts Many-to-One Model

Silberschatz, Galvin and Gagne  Operating System Concepts One-to-One Each user-level thread maps to kernel thread. Examples - Windows 95/98/NT/ OS/2

Silberschatz, Galvin and Gagne  Operating System Concepts One-to-one Model

Silberschatz, Galvin and Gagne  Operating System Concepts 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. Solves the blocking problem while maintaining efficient thread creation and management. Solaris 2 Windows NT/2000 with the ThreadFiber package

Silberschatz, Galvin and Gagne  Operating System Concepts Many-to-Many Model

Silberschatz, Galvin and Gagne  Operating System Concepts Threading Issues Semantics of fork() and exec() system calls. If multithreaded process forks a child, does the child process have the same number of active threads? Thread cancellation. Immediate or deferred cancellation. Signal handling The O.S. uses a signal to notify a process that an event has occurred. If process is multithreaded, where to deliver signal? Thread pools Reuse threads in some applications – web server Thread specific data Thread tables handle thread specific data the way PCBs handle process specific data.

Silberschatz, Galvin and Gagne  Operating System Concepts 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.

Silberschatz, Galvin and Gagne  Operating System Concepts Solaris 2 Threads

Silberschatz, Galvin and Gagne  Operating System Concepts Solaris Process Several light weight processes can belong to a Solaris process (kernel thread)

Silberschatz, Galvin and Gagne  Operating System Concepts Windows 2000 Threads Implements the one-to-one mapping. Each thread contains - a thread id - register set - separate user and kernel stacks - private data storage area

Silberschatz, Galvin and Gagne  Operating System Concepts 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)

Silberschatz, Galvin and Gagne  Operating System Concepts Java Threads Java threads may be created by:  Extending Thread class  Implementing the Runnable interface Java threads are managed by the JVM.

Silberschatz, Galvin and Gagne  Operating System Concepts Java Thread States