Processes, threads and synchronization

Short Description
Here we will discuss the fundamental notions which are processes and threads, in the architecture of the Windows NT/2000/XP operating systems. You must keep in mind that the CLR described in the previous chapter is a software layer loaded into a process by the runtime host when a .NET assembly is launched.

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Content
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Introduction
A process is a memory region containing resources. The process allows to the operating system to split its work amongst several functional units.
A process owns one or several execution units called threads. A process also owns a private virtual addressing space which can be only accessed by its own threads.
When running .NET programs, a process also contains in its memory space a software layer called the CLR. A detailed description of the CLR was done in the previous chapter. This software layer is loaded during the creation of the process by the runtime host (which is described at page 76).
A thread can only belong to a single process and can only uses the resources of this process. When a process is created by the operating system, it automatically allocates a thread called the main thread or primary thread. It is this thread which executes the runtime host, who in turn loads the CLR.
An application is made from one or several cooperating processes. For example, the Visual Studio development environment is an application which can use one process to edit the source files and another for the compilation.
Under the Windows NT/2000/XP operating systems, we can see at any given time all the applications and processes by launching the task manager tool. It is common to have about thirty processes running at the same time, even if you only have opened only a few applications. In fact, the system executes a large number of processes, for the management of the current session, for the management of the task bar and for several other tasks.
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