operating system《操作系統(tǒng)》ch04-thread

1、整理課件4.2nTo introduce the notion of a thread - a fundamental unit of CPU utilization that forms the basis of multithreaded computer systems.nTo discuss the APls for Phtreads, Win32, and Java thread libraries.4.3nOverviewnMultithreading ModelsnThreading IssuesnPthreadsnWindows XP ThreadsnLinux Threads

2、nJava Threads4.4nA thread is a basic unit of CPU utilization; nIt comprises a thread ID, a program counter, a register set, and a stack.nIt shares with other threads belonging to the same process its code section, data section, and other operating-system resources, such as open files and signals. 4.

3、54.6nResponsivenessnResource SharingnEconomynUtilization of MP Architectures4.7nUser threads are supported above the kernel and are managed without kernel support,Thread management done by user-level threads librarynkernel threads are supported and managed directly by the operating system.,Supported

4、 by the Kernel 4.8nUltimately, there must exist a relationship between user threads and kernel threads.nMany-to-OnenOne-to-OnenMany-to-Many4.9nMany user-level threads mapped to single kernel threadnExamples:lSolaris Green ThreadslGNU Portable ThreadsnThread management is done by the thread library i

5、n user space, so it is efficient;nbut the entire process will block if a thread makes a blocking system call.nbecause only one thread can access the kernel at a time, multiple threads are unable to run in parallel on multiprocessors.4.104.11nEach user-level thread maps to a kernel threadnIt provides

6、 more concurrency than the many-to-one model by allowing another thread to run when a thread makes a blocking system call; nit also allows multiple threads to run in parallel on multiprocessors. nThe only drawback is that creating a user thread requires creating the corresponding kernel thread, so r

7、estriction to the number of threads supported by the system is neccesarynExampleslWindows NT/XP/2000lLinuxlSolaris 9 and later4.124.13nAllows many user level threads to be mapped to many kernel threadsnAllows the operating system to create a sufficient number of kernel threadsnSolaris prior to versi

8、on 9nWindows NT/2000 with the ThreadFiber package4.144.15nSimilar to M:M, except that it allows a user thread to be bound to kernel threadnExampleslIRIXlHP-UXlTru64 UNIXlSolaris 8 and earlier4.164.17nprovides the programmer an API for creating and managing threads. ntwo primary ways of implementing

9、a thread library. lprovide a library entirely in user space with no kernel support. All code and data structures for the library exist in user space. This means that invoking a function in the library results in a local function call in user space and not a system call.limplement a kernel-level libr

10、ary supported directly by the operating system. In this case, code and data structures for the library exist in kernel space. Invoking a function in the API for the library typically results in a system call to the kernel.nThree main thread libraries are in use (1) POSIX Pthreads, (2) Win32, and (3)

11、 Java.4.18nA POSIX standard (IEEE 1003.1c) API for thread creation and synchronizationnAPI specifies behavior of the thread library, implementation is up to development of the librarynCommon in UNIX operating systems (Solaris, Linux, Mac OS X)4.19nImplements the one-to-one mappingnEach thread contai

12、nslA thread idlRegister setlSeparate user and kernel stackslPrivate data storage areanThe register set, stacks, and private storage area are known as the context of the threadsnThe primary data structures of a thread include:lETHREAD (executive thread block)lKTHREAD (kernel thread block)lTEB (thread

13、 environment block)4.20nJava threads are managed by the JVMnJava threads may be created by:lExtending Thread classlImplementing the Runnable interface4.214.22nSemantics of fork() and exec() system callsnThread cancellationnSignal handlingnThread poolsnThread specific datanScheduler activations4.23nD

14、oes fork() duplicate only the calling thread or all threads?4.24nTerminating a thread before it has finishednTwo general approaches:lAsynchronous cancellation terminates the target thread immediatelylDeferred cancellation allows the target thread to periodically check if it should be cancelled4.25nS

15、ignals are used in UNIX systems to notify a process that a particular event has occurrednA signal handler is used to process signalslSignal is generated by particular eventlSignal is delivered to a processlSignal is handlednOptions:lDeliver the signal to the thread to which the signal applieslDelive

16、r the signal to every thread in the processlDeliver the signal to certain threads in the process1.Assign a specific threa to receive all signals for the process4.26nCreate a number of threads in a pool where they await worknAdvantages:lUsually slightly faster to service a request with an existing th

17、read than create a new threadlAllows the number of threads in the application(s) to be bound to the size of the pool4.27nAllows each thread to have its own copy of datanUseful when you do not have control over the thread creation process (i.e., when using a thread pool)4.28nBoth M:M and Two-level models require communication to mai