This distinction has led to the development, in many operating systems, of a construct known as the thread.After examining threads,we look at symmetric multiprocessing (SMP). With SMP, the OS must be able to simultaneously schedule different processes on multiple processors. Finally, we introduce the concept of the microkernel,which is an effective means of structuring the OS to support process management and its other tasks.
The discussion so far has presented the concept of a process as embodying two
characteristics:
• Resource ownership: A process includes a virtual address space to hold the
process image; recall from Chapter 3 that the process image is the collection of
program, data, stack, and attributes defined in the process control block. From
time to time, a process may be allocated control or ownership of resources,
such as main memory, I/O channels, I/O devices, and files. The OS performs a
protection function to prevent unwanted interference between processes with
respect to resources.
• Scheduling/execution: The execution of a process follows an execution path
(trace) through one or more programs (e.g., Figure 1.5 and Figure 1.26). This
execution may be interleaved with that of other processes.Thus, a process has
an execution state (Running, Ready, etc.) and a dispatching priority and is the
entity that is scheduled and dispatched by the OS.
Some thought should convince the reader that these two characteristics are independent
and could be treated independently by the OS.This is done in a number
of operating systems, particularly recently developed systems.To distinguish the two
characteristics, the unit of dispatching is usually referred to as a thread or lightweight
process, while the unit of resource ownership is usually still referred to as a process
or task.1
Multithreading
Multithreading refers to the ability of an OS to support multiple, concurrent paths of execution within a single process.The traditional approach of a single thread of execution per process, in which the concept of a thread is not recognized, is referred to as a single-threaded approach. The two arrangements will be discussed in details in next sections. MS-DOS is an example of an OS that
supports a single user process and a single thread. Other operating systems, such as
some variants of UNIX, support multiple user processes but only support one
thread per process.The multithreaded approaches also will be discussed.A Java run-time environment is an example of a system of one process with multiple
threads. Of interest in this section is the use of multiple processes, each of which support
multiple threads.This approach is taken in Windows, Solaris, and many modern
versions of UNIX, among others. In this section we give a general description of
multithreading; the details of the Windows, Solaris, and Linux approaches are discussed
later in this chapter.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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