IPC interprocess communication between Linux environments (i): IPC overview

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".

IPC is the abbreviation for interprocess communication, which is a way of delivering various messages between different processes running on an operating system. There are several ways to IPC: Pipelines, FIFO (also known as pipes), Message Queuing, sockets, remote Procedure Call (RPC). Pipelines can only be used between processes that have a common ancestor (referred to as a parent-child process relationship), but the FIFO (known pipe) solves the problem, and Message Queuing can be used between affinity and unrelated processes on the same host; A remote procedure call is a way for a program on a system (client host) to invoke a function on another system (server host), developed as an alternative to display network programming, since some information is usually passed between the client and the server (the parameters of the called function and the return value). RPC can be thought of as another form of messaging, while RPCs are available between clients and servers on the same host.

Figure Three ways to share information between processes

The two processes on the left share some information that resides on a file in the file system, and the two processes in the middle share some information residing in the kernel; the two processes on the right have a shared memory area that can be accessed by both parties. Although only two processes are drawn in the figure, the implementation can be any number of processes. All threads within a given process share the same global variables (that is, the concept of a shared memory area is intrinsic to the thread). However, we must focus on synchronous access to global data between each thread. Therefore, synchronization may not be treated as an IPC form, but is used in many IPC forms to control access to certain shared data.

three ways to share information from the three above can be seen in the IPC's three sustainability, that is, how long an IPC object has been in existence .

Figure the continuity of IPC objects

IPC type	Continuity of
Pipeline Fifo	With process With process
posix read/write lock posix Mutex posix condition variable fcntl record lock	with process with process with process with process
posix Message Queuing posix known semaphore POSIX memory-based semaphore posix shared memory area	with kernel with kernel with process Span style= "Font-family:microsoft Yahei; Font-size:14px "> with kernel
system v Message Queuing system v Semaphore system shared memory area	with kernel with kernel with kernel
TCP sockets UDP sockets UNIX domain sockets	With process With process With process

Diagram of the persistence of various types of IPC objects

There is no type of IPC with the persistence of the file system, three types of Posix IPC may have that continuity, but depend on the implementation. In fact , writing data to a file provides continuity with the file system, but this is not used as an IPC form. Most forms of IPC are not necessary to continue to exist after the system has been re-raised because the process does not exist after it has been self-raised. Furthermore, for a given form of IPC, the requirement to have the continuity of the file system may degrade its performance, while the IPC is a basic design target with high performance.

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