Windows System Programming Third Edition [Electronic resources] نسخه متنی

Windows Processes and Threads

Every process contains one or more threads, and the Windows thread is the basic executable unit. Threads are scheduled on the basis of the usual factors: availability of resources such as CPUs and physical memory, priority, fairness, and so on. Windows has supported symmetric multiprocessing (SMP) since NT4, so threads can be allocated to separate processors within a system.

From the programmer's perspective, each Windows process includes resources such as the following components:

• One or more threads.

• A virtual address space that is distinct from other processes' address spaces, except where memory is explicitly shared. Note that shared memory-mapped files share physical memory, but the sharing processes will use different virtual addresses to access the mapped file.

• One or more code segments, including code in DLLs.

• One or more data segments containing global variables.

• Environment strings with environment variable information, such as the current search path.

• The process heap.

• Resources such as open handles and other heaps.

Each thread in a process shares code, global variables, environment strings, and resources. Each thread is independently scheduled, and a thread has the following elements:

• A stack for procedure calls, interrupts, exception handlers, and automatic storage.

• Thread Local Storage (TLS)arrays of pointers giving each thread the ability to allocate storage to create its own unique data environment.

• An argument on the stack, from the creating thread, which is usually unique for each thread.

• A context structure, maintained by the kernel, with machine register values.

Figure 6-1 shows a process with several threads. This figure is schematic and does not indicate actual memory addresses, nor is it drawn to scale.

This chapter shows how to work with processes consisting of a single thread. Chapter 7 shows how to use multiple threads.

Note:
Figure 6-1 is a high-level overview from the programmer's perspective. There are numerous technical and implementation details, and interested readers can find out more in Inside Windows 2000 (Solomon and Russinovich).