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This article shows you the concept of process and thread in Linux and what is the difference. The content is concise and easy to understand, which can definitely brighten your eyes. I hope you can get something through the detailed introduction of this article.

The difference between linux processes and threads has long been a hot topic in the IT world. Whether you are a junior programmer or a senior expert, you should consider this problem, but from a different point of view. For ordinary programmers, understanding the concept of the two and learning to use them in their work is the main problem they think about; for senior engineers, how to implement the two technologies at the system level and their respective performance and implementation cost is the main problem they think about. This shows the important position of processes and threads in the IT world.

Processes and threads are the basic concepts of the operating system, and there are both differences and connections between them. By definition, they are abstract and difficult to understand. Today, I will give you an analogy to teach you to understand it and master it by analogy. In fact, the relationship between the process and the thread is like the relationship between the factory workshop and the workers in the workshop. The process is like a factory workshop, and the thread is like the workers in the workshop. Each factory workshop has an entrance and an exit. This is like the main function of executing the process program. Each factory workshop has its own address space, which can contain workers of different types of work, which is like the address space of a process, including text area, number area, stack; a factory workshop can accommodate 1 or n workshop workers, processes and threads have an one-to-one or one-to-many relationship, and a process contains at least one thread The workers in the workshop share the space in the workshop, which symbolizes that the memory space of a process is shared, and each thread can use the shared memory. Each workshop can be used by different workers, but the size of each workshop is different, and there is an upper limit for the number of people. For example, each toilet can hold one person, and each kitchen can hold n people. But every worker in the workshop has the need to go to the toilet and eat, so how to solve this problem? Do it in batches! This is like a lock mechanism in a thread. When n threads compete for the same resource, a lock is added to the resource. When the thread is finished, the resource will be released for later use. One might ask, how do you determine the order in which the resource is used? It is determined according to the level of priority, those with high priority are used first, those with low priority are used later, and the same level is used in the first-come-first-served order.

From this story, we can see that the design of the operating system can be summarized into three points:

(1) in the form of multiple processes, multiple tasks are allowed to run at the same time, that is, multiple workshops in the factory are allowed to work at the same time.

(2) in the form of multithreading, a single task is allowed to run in different parts, that is, different types of work in the same workshop are allowed to complete different tasks.

(3) provide a coordination mechanism to prevent conflicts between processes and threads on the one hand and share resources between processes and threads on the other.

After we have a basic concept of processes and threads, let's take a look at the differences between processes and threads:

(1) the execution process of a process is sequential, and although interruptions or pauses may occur during execution, the resources owned by the process only serve the linear execution process. Just like a factory that can only supply power to one workshop at a time, when one workshop An is working and another more advanced workshop B is about to start work, then workshop A will lose power, but all the facilities and location of workshop A will not change. Workshop A will continue to work when the power of workshop B is cut off. This is the linear execution of the process macroscopically. On the other hand, the change of the thread only changes the CPU execution process, without the change of the resources owned by the process. In addition to CPU, the allocation of software and hardware resources in the computer has nothing to do with the thread, which can only share the resources of the process to which it belongs. It's like the workers in a workshop. They can change places, but they are still in the same workshop.

(2) there is a difference between a process and a thread in the process of execution. A process is an executing program, and each independent process has an entry, a sequential execution sequence and an exit of the program, which is the main function of the program. However, threads cannot execute independently and must be stored in the application, which provides multiple thread execution control. Just like each workshop has an import and export, you can produce a separate product, but this depends on the workers in the workshop to work together to complete.

(3) through the execution process of process and thread, we can see that there is an one-to-one or one-to-many relationship between process and thread. A process contains at least one thread, and the process has a complete virtual address space. The size of its space is determined when it is designed, and does not change with the number and size of workers, that is to say, it exists independently of threads. On the contrary, a thread is part of a process, does not have its own address space, and shares all resources assigned to that process with other threads within the process.

(4) Thread can effectively improve the execution efficiency of the system in real-time systems where process scheduling and switching are rarely done, but it is not applicable in all computer systems. This is like the same workshop workers always do the same product production capacity is higher than often switch workshops, switch jobs, do different products, because they change workshops, familiar with the environment, familiar with the production process takes time. This means that the creation of threads is much less expensive than the creation of processes.

(5) from a logical point of view, the significance of multithreading lies in an application, they can achieve multiple functions of the application, but can not achieve a complete application. Just like producing a complex product, each workshop only produces one or more parts of the product, and a finished product still depends on the whole factory. In other words, the scheduling and management of processes and the allocation of resources still depend on the operating system, which is an important difference between processes and threads.

The above is the concept of process and thread in Linux and what is the difference. Have you learned any knowledge or skills? If you want to learn more skills or enrich your knowledge reserve, you are welcome to follow the industry information channel.

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