Linux inter-process communication methods and techniques: how to let processes communicate and collaborate with each other

Inter-process communication refers to the transfer and sharing of data between different processes in the Linux system to achieve communication and collaboration between processes. The purpose of inter-process communication is to improve the concurrency and efficiency of the system to complete some complex tasks and functions. There are many methods of inter-process communication, such as pipes, message queues, signals, shared memory, semaphores, sockets, etc. Each of them has its own characteristics, advantages and disadvantages, and is suitable for different scenarios and needs. But, do you really understand how Linux inter-process communication works? Do you know how to use and choose the appropriate inter-process communication method under Linux? Do you know how to optimize and improve the effectiveness of inter-process communication under Linux? This article will introduce you to the relevant knowledge of Linux inter-process communication in detail, allowing you to better use and understand this powerful kernel function under Linux.

The concept of process

Process is the concept of the operating system. Whenever we execute a program, a process is created for the operating system. In this process, resources are allocated and released. A process can be thought of as an execution of a program.

Concept of process communication

Process user spaces are independent of each other and generally cannot access each other. But in many cases, processes need to communicate with each other to complete a certain function of the system. Processes coordinate their behavior by communicating with the kernel and other processes.

Application scenarios of process communication

Data transfer: One process needs to send its data to another process, and the amount of data sent ranges from one byte to several megabytes.

Shared data: Multiple processes want to operate shared data. If one process modifies the shared data, other processes should see it immediately.

Notification event: A process needs to send a message to another process or a group of processes to notify it (them) that a certain event has occurred (such as notifying the parent process when the process terminates).

Resource sharing: Sharing the same resources between multiple processes. In order to do this, the kernel needs to provide locking and synchronization mechanisms.

Process control: Some processes hope to completely control the execution of another process (such as the Debug process). At this time, the control process hopes to intercept all traps and exceptions of another process and be able to know its status changes in time.

Methods of process communication

1. Pipeline

Pipes are divided into named pipes and unnamed pipes

The unnamed pipe is a half-duplex communication method. Data can only flow in one direction and can only be used between processes with affinity. The affinity of a process generally refers to the parent-child relationship. Ignorance pipes are generally used for communication between two different processes. When a process creates a pipe and calls fork to create a child process of its own, the parent process closes the read pipe end and the child process closes the write pipe end. This provides a way for data to flow between the two processes.

The famous pipe is also a half-duplex communication method, but it allows communication between unrelated processes.

2.Semaphore

The semaphore is a counter that can be used to control multiple threads' access to shared resources. It is not used to exchange large amounts of data, but is used for synchronization between multiple threads. It is often used as a lock mechanism to prevent When a process accesses a resource, other processes also access the resource. Therefore, it is mainly used as a means of synchronization between processes and between different threads within the same process.

Linux provides a set of carefully designed semaphore interfaces to operate signals. They are not just for binary semaphores. These functions will be introduced below, but please note that these functions are used to group The semaphore value is operated on. They are declared in the header file sys/sem.h.

semget function

Its function is to create a new semaphore or obtain an existing semaphore

semop function

Its function is to change the value of the semaphore

semctl function

This function is used to directly control the semaphore information

3. Signal

Signal is a relatively complex communication method used to notify the receiving process that an event has occurred.

4. Message Queue

The message queue is a linked list of messages, which is stored in the kernel and identified by the message queue identifier. The message queue overcomes the characteristics of less signal transmission information, the pipeline can only carry unformatted byte streams, and the limited buffer size. Message Queue is a mechanism that allows different processes to share resources under UNIX. UNIX allows different processes to send formatted data streams to any process in the form of message queues. Processes with operating permissions on the message queue can use msget to complete the query. Operational control of message queues. By using message types, processes can read messages in any order, or prioritize messages.

5.Shared memory

Shared memory is to map a section of memory that can be accessed by other processes. This shared memory is created by one process, but can be accessed by multiple processes. Shared memory is the fastest IPC (inter-process communication) method, it is It is specially designed for the low operating efficiency of other inter-process communication methods. It is often used in conjunction with other communication mechanisms, such as semaphores, to achieve synchronization and communication between processes.

6. Socket

Socket, that is, socket is a communication mechanism. With this mechanism, the development of client/server (that is, the process to communicate) system can be carried out on a local single machine or across a network. That is, it allows processes on computers that are not on the same computer but are connected through a network to communicate. Because of this, sockets clearly distinguish clients from servers.

The characteristics of the socket are determined by 3 attributes: domain, type and protocol.

Through this article, you should have a comprehensive understanding of Linux inter-process communication methods, and know their definition, principles, usage, advantages and disadvantages. You should also understand the purpose and impact of inter-process communication, and how to correctly use and choose inter-process communication methods under Linux. We recommend that you use inter-process communication to improve system concurrency and efficiency when using a Linux system. At the same time, we also remind you to pay attention to some potential issues and challenges when using inter-process communication, such as synchronization, security, performance, etc. I hope this article can help you better use the Linux system and allow you to enjoy the advantages and convenience of inter-process communication under Linux.

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