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This article mainly introduces the relevant knowledge of "how to understand processes and threads". The editor shows you the operation process through an actual case, and the operation method is simple, fast and practical. I hope this article "how to understand processes and threads" can help you solve the problem.

The situation of a single-task system

In this case, all system resources are handed over to the program, and the programmer only needs to consider the flow and logic of processing. The resources here include: CPU time, memory (heap, stack), global variables, hardware devices (monitor, keyboard, communication interface, audio device) and so on.

The situation of multitasking operating system

Process

Ideally for programmers, there is no need to realize that you are writing programs in a multitasking operating system environment.

In other words, at least it seems that all the system resources are left to the program, and the programmer only needs to consider the flow and logic of processing. The resources here include: CPU time, memory (heap, stack, global variables), hardware devices (monitor, keyboard, communication interface, audio device), etc.

But the problem is that there is only one physical memory and only one device, and competition is bound to occur when multiple programs are executed at the same time. Of course, we don't have to consider this problem, because the multitasking operating system has been solved:

Provide a certain amount of CPU time for each program to ensure that the program can be executed at some interval. This execution is at the binary machine code level.

Each program is provided with independent, virtual memory space, and the actual memory operations are mapped to the actual physical memory.

For the display part, a window mechanism is provided to direct the output of the program to a specific window. At the same time, the system directs the output of the keyboard and mouse to the currently active window.

Some hardware, such as audio input devices and serial ports, cannot be shared between programs. Such hardware is used in an exclusive manner, and if one program occupies a device, other programs cannot be used.

After all this, it can be said that our ideal has been basically realized: programmers do not have to realize that they actually provide programs for multitasking operations. Each task is designed and implemented as a separate program, and the scheduling between tasks is realized by using the functions of the operating system.

The execution process of such a program is the process. Basically, a process is equivalent to an application in a multitasking operating system.

The advantage of the process is to maximize the independence of the program execution process, making it easy to add tasks or adjust task content. But at the same time, you can also see that the operating system allocates resources for each, maps memory operations, and various inputs and outputs. All of these require considerable system overhead. Therefore, the interior of the multitasking operating system is gradually developed with the improvement of hardware performance.

Thread

After understanding the pros and cons of the process, it is easy to understand threads. In many cases, multitasking is still needed within a process, for example, when video is being decoded, the software has to accept user operations. In this case, you need to provide a multitasking mechanism within the process: threads.

The allocation of CPU time between threads in a process is similar to that of a process, but the resources of the process are shared, and the operating system does not have to provide another mapping mechanism for each thread.

When multiple threads share a resource, programmers are required to actively access control and synchronize using the interface provided by the operating system.

Because it is used for common memory space, heap, stack and so on, it does not need additional address mapping and other processing, and can achieve relatively fast data exchange.

This is the end of the content about "how processes and threads understand". Thank you for reading. If you want to know more about the industry, you can follow the industry information channel. The editor will update different knowledge points for you every day.

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