What are the methods of inter-process communication in Linux?

Linux inter-process communication methods include: 1. Pipes (including anonymous pipes and named pipes); 2. Signals; 3. Message queues; 4. Shared memory; 5. Semaphores; 6. Sockets . The essence of the pipe is a kernel buffer, and the process uses the pipe to transfer information.

Linux inter-process communication method:

(Recommended learning: linux tutorial)

The basic communication methods between Linux processes mainly include: pipes (including anonymous pipes and named pipes), signals, message queues, shared memory, semaphores and sockets.

The following methods are introduced respectively:

1. Pipeline

The essence of a pipe is a kernel buffer. As the name suggests, the two processes that need to communicate are at both ends of the pipe, and the processes use the pipe to transfer information. For the processes at both ends of the pipe, a pipe is a file, but this file is special. It does not belong to the file system and only exists in memory.

2. Signal

The signal is a simulation of the interrupt mechanism at the software level. It is an asynchronous communication method. The process does not have to wait for the signal through any operation. arrive. Signals can directly interact between user space processes and the kernel, and the kernel can use signals to notify user space processes of what system events have occurred.

3. Message Queue

The message queue is a linked list of messages, with a specific format, stored in memory and identified by the message queue identifier, and allows one or Multiple processes write and read messages to it

4. Shared memory

enables multiple processes to directly read and write the same memory space, which is for other Communication mechanisms are designed to operate inefficiently.

In order to exchange information between multiple processes, the kernel specially sets aside a memory area, which can be mapped to its own private address space by the process that needs to access it. The process can directly read and write this memory without copying the data, thus greatly improving efficiency.

Note: Shared memory does not provide a synchronization mechanism. Before one process finishes writing to the shared memory, there is no automatic mechanism to prevent another two processes from starting to read it. Therefore, we usually need to use other mechanisms to synchronize access to shared memory.

5. Semaphore

The semaphore is essentially a counter that identifies the number of available resources, and its value is always a non-negative integer. Semaphores with only two values ​​​​0 and 1 are called binary semaphores (or binary semaphores), which can be used to identify whether a certain resource is available.

6. Sockets

Sockets are a more basic inter-process communication mechanism. Unlike other methods, sockets can be used on different machines. inter-process communication.

There are two types of sockets: file-based and network-oriented.

(1) Unix sockets are file-based and have a "family name" - AF_UNIX, which represents the address family: UNIX.

(2) The second type of socket is based on the network. It also has its own family name-AF_INET, which represents the address family (address family): INTERNET

No matter which one is used Address families, all have two different types of socket connections: connection-oriented and connectionless.

(1) Connection-oriented socket (SOCK_STREAM)

A connection must be established before communication. Connection-oriented communication provides serialized, reliable and non-duplicate data delivery. There are no record boundaries.

This means that each piece of information can be split into multiple fragments, and each fragment is guaranteed to reach the destination, and then the information is spliced ​​together at the destination.

The main protocol that implements this connection type is the Transmission Control Protocol (TCP).

(2) Connectionless socket (SOCK_DGRAM)

There is no need to establish a connection before communication starts, and its sequence, reliability or reliability cannot be guaranteed during data transmission. Repeatability.

However, datagrams do preserve record boundaries, which means that the message is sent as a whole rather than first broken into fragments.

Because of the guarantees provided by connection-oriented sockets, their setup and maintenance of virtual circuit connections requires significant overhead. However, datagrams do not require this overhead, i.e. they are more "cheap".

The main protocol that implements this connection type is the User Datagram Protocol (UDP).

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