操作系统ch5.pptVIP

Chapter 5: Threads Overview Multithreading Models Threading Issues Pthreads Solaris 2 Threads Windows 2000 Threads Linux Threads Java Threads 线程的引入 传统进程既是除处理机以外的资源分配单位（如内存占用单位），又是执行单位。随着共享内存多外理机的发展，为了支持进程内多道程序设计而引入线程。 新结构对操作系统的要求 多任务并行支持。希望同一进程的程序可同时在多CPU上运行，同时还共享进程存储空间。 同步支持。当运行在不同CPU上的程序访问共享数据时，要有利用硬件支持的同步手段(如：读后置1）。 每个CPU都应该能够运行操作系统调度程序进行自行调度。 多CPU cache一致性的要求(全部由硬件实现或由硬件和操作系统合作实现) 三、线程状态变化 进程产生时同时产生第一个线程，其他线程在以后由任一线程请求创建。 线程创建后运行过程中的三个主要状态是：运行、就绪、阻塞。 在SPARC工作站上不同线程、进程操作开销比较 Single and Multithreaded Processes User Threads Thread management done by user-level threads library Examples - POSIX Pthreads - Mach C-threads - Solaris threads Kernel Threads Supported by the Kernel Examples - Windows 95/98/NT/2000 - Solaris - Tru64 UNIX - BeOS - Linux Multithreading Models Many-to-One One-to-One Many-to-Many Many-to-One Many user-level threads mapped to single kernel thread. Used on systems that do not support kernel threads. Many-to-One Model One-to-One Each user-level thread maps to kernel thread. Examples - Windows 95/98/NT/2000 - OS/2 One-to-one Model 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 2 Windows NT/2000 with the ThreadFiber package Many-to-Many Model Threading Issues Semantics of fork() and exec() system calls.:different. Thread cancellation.: Signal handling: Thread pools: Thread specific data Pthreads 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 2 Threads Solaris Process 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 Linux Threads Linux refers to them as tasks rather than threads. Thread creation is don