Prepare for interview 1 (interprocess communication)

Inter-process communication is the transmission or exchange of information between different processes, so what is there between the different processes that can be accessed by both parties? The user space of the process is independent of each other and is generally inaccessible to each other, with the only exception being the shared memory area. However, the system space is a "public place", so the kernel can obviously provide such conditions. In addition, it is a peripheral that can be accessed by both parties. In this sense, two processes can of course also exchange information through ordinary files on disk, or through "registry" or some table entries and records in other databases. Broadly speaking, this is also a means of inter-process communication, but it is generally not counted as "interprocess communication". Because the efficiency of those communication means is too low, and people's requirements for inter-process communication is to have a certain real-time nature.

Inter-process communication mainly includes pipelines, system IPC (including message queue, semaphore, shared storage), SOCKET.

The pipeline consists of three kinds: 1) Common pipe pipes, usually have a limit, one half-duplex, only one-way transmission, and second, can only be used between parent-child processes. 2) Flow pipe s_pipe: Remove the first restriction, can be transmitted in both directions. 3) Named pipes: Name_pipe, which removes the second limitation, can communicate between many unrelated processes.

The three ways in which the system IPC is similar are identified using the identifiers in the kernel.

# pipe: A pipe is a half-duplex mode of communication in which data can only flow in one direction and can only be used between processes that have affinity. A process's affinity usually refers to a parent-child process relationship.

# famous pipe (named pipe): A well-known pipe is also a half-duplex mode of communication, but it allows communication between unrelated processes.

# semaphore (Semophore): Semaphore is a counter that can be used to control access to shared resources by multiple processes. It is often used as a locking mechanism to prevent a process from accessing the shared resource while other processes are accessing the resource. Therefore, it is primarily used as a means of synchronization between processes and between different threads within the same process.

# message Queue: Message Queuing is a linked list of messages that are stored in the kernel and identified by message queue identifiers. Message Queuing overcomes the disadvantages of less signal transmission information, only unformatted byte stream, and limited buffer size.

# signal (sinal): A signal is a more sophisticated means of communication that notifies the receiving process that an event has occurred.

# Shared Memory: Shared memory is the mapping of memory that can be accessed by other processes, which is created by a process, but can be accessed by multiple processes. Shared memory is the fastest IPC approach and is specifically designed for low-efficiency operation of other interprocess communication modes. It is often used with other communication mechanisms, such as signal two, to achieve synchronization and communication between processes.

# Socket: Socket is also an inter-process communication mechanism, unlike other communication mechanisms, which can be used for process communication between different processes.

Prepare for interview 1 (interprocess communication)