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This article mainly introduces how to achieve inter-process communication, the article is very detailed, has a certain reference value, interested friends must read it!

The ways of inter-process communication are: 1, pipes usually refer to unnamed pipes, which is the oldest form of UNIX system IPC; 2, FIFO, is a file type; 3, message queue, is a linked list of messages, stored in the kernel; 4, semaphores, is a counter; 5, shared memory.

The ways to communicate between processes are:

I. Pipeline

Pipes, usually unnamed pipes, are the oldest form of UNIX system IPC.

Features:

It is half-duplex (that is, data can only flow in one direction) and has a fixed reader and writer.

It can only be used for communication between related processes (also between parent-child or sibling processes).

It can be regarded as a special file, and ordinary read, write and other functions can also be used for its reading and writing. But it is not an ordinary file, does not belong to any other file system, and exists only in memory.

II. FIFO

FIFO, also known as named pipes, is a file type.

1. Characteristics

FIFO can exchange data between unrelated processes, unlike unnamed pipes.

FIFO has a pathname associated with it, and it exists in the file system as a special device file.

Message queuing

Message queues, which are linked lists of messages, are stored in the kernel. A message queue is identified by an identifier, the queue ID.

Characteristics

Message queues are record-oriented, where messages have a specific format and a specific priority.

Message queuing is independent of the sending and receiving processes. When the process terminates, the message queue and its contents are not deleted.

Message queuing can query messages randomly. Messages do not have to be read in first-in-first-out order, but can also be read according to the type of message.

IV. Semaphore

Unlike the IPC structure that has been introduced, the semaphore (semaphore) is a counter. Semaphores are used to achieve mutual exclusion and synchronization between processes, rather than to store inter-process communication data.

Characteristics

Semaphores are used for inter-process synchronization, and shared memory is needed to transfer data between processes.

The semaphore is based on the PV operation of the operating system, and the operation of the program to the semaphore is atomic.

Each PV operation on the semaphore is not only limited to add or subtract 1 to the semaphore value, but also can add or subtract any positive integer.

Semaphore groups are supported.

5. Shared memory

Shared memory (Shared Memory) means that two or more processes share a given storage area.

Characteristics

Shared memory is the fastest IPC because the process accesses memory directly.

Because multiple processes can operate at the same time, synchronization is required.

Semaphores + shared memory are usually used together, and semaphores are used to synchronize access to shared memory.

The above is all the contents of the article "how to achieve inter-process communication". Thank you for reading! Hope to share the content to help you, more related knowledge, welcome to follow the industry information channel!

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