进程间通信(IPC)的方法:UNIX域套接字

UNIX域套接字(UNIX domain socket)为我们提供了一种在进程之间建立通信通道的便捷方法，具有许多有用的内置功能。它支持面向流(TCP)和面向数据报(UDP)协议作为TCP/IP互联网套接字。我们还可以在阻塞和非阻塞模式之间进行选择。
首先需要创建套接字并在套接字函数中指定AF_UNIX作为域套接字。创建套接字后，必须使用绑定函数将套接字绑定到唯一的文件路径。与AF_INET域中的Internet套接字绑定到唯一的IP地址和端口号不同，UNIX域套接字绑定到文件路径。文件系统中创建的此文件，当程序关闭且不再需要该文件时，你必须手动将其删除。
UNIX域套接字与server/client网络套接字通信没有太大不同，但它旨在供本地文件系统使用。server/client网络套接字介绍参考：https://blog.csdn.net/fengbingchun/article/details/107848160

UNIX域套接字总结：
(1).同步；
(2).极高的吞吐量；存储设备速度限制；
(3).双向通信；
(4).以线性方式读写；
(5).自动内存管理。

注：以上内容主要来自网络整理。

测试代码如下：

#include <unistd.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/wait.h>
#include <string.h>
#include <errno.h>
#include <iostream>int main()
{// reference: https://biendltb.github.io/tech/inter-process-communication-ipc-in-cpp/const char* server_sock_path = "/tmp/unix_sock.server";const char* client_sock_path = "/tmp/unix_sock.client";pid_t pid = fork(); // create two processes of client and serverif (pid < 0) {fprintf(stderr, "fail to fork\n");return -1;}if (pid != 0) { // server process(parent process)auto server_sock = socket(AF_UNIX, SOCK_STREAM, 0); // open the server socket with the SOCK_STREAM typeif (server_sock == -1) {fprintf(stderr, "SERVER: fail to socket: %s\n", strerror(errno));exit(1);}// bind to an address on file system// similar to other IPC methods, domain socket needs to bind to a file system, so that client know the address of the server to connect tostruct sockaddr_un server_addr;memset(&server_addr, 0, sizeof(server_addr));server_addr.sun_family = AF_UNIX;strcpy(server_addr.sun_path, server_sock_path);unlink(server_sock_path); // unlink the file before bind, unless it can't bind: error info: Address already in useauto rc = bind(server_sock, (struct sockaddr *)&server_addr, sizeof(server_addr));if (rc == -1) {fprintf(stderr, "SERVER: fail to bind: %s\n", strerror(errno));exit(1);}// listen and accept client connection// set the server in the "listen" mode and maximum pending connected clients in queuerc = listen(server_sock, 10);if (rc == -1) {fprintf(stderr, "SERVER: fail to listen: %s\n", strerror(errno));exit(1);}fprintf(stdout, "SERVER: Socket listening...\n");struct sockaddr_un client_addr;auto len = sizeof(client_addr);int client_fd = accept(server_sock, (struct sockaddr *)&client_addr, (socklen_t*)&len);if (client_fd == -1) {fprintf(stderr, "SERVER: fail to accept: %s\n", strerror(errno));exit(1);}fprintf(stdout, "SERVER: Connected to client at: %s\n", client_addr.sun_path);fprintf(stdout, "SERVER: Wating for message...\n");const int buf_len = 256;char buf[buf_len];memset(buf, 0, buf_len);int byte_recv = recv(client_fd, buf, buf_len, 0);if (byte_recv == -1) {fprintf(stderr, "SERVER: fail to recv: %s\n", strerror(errno));exit(1);}elsefprintf(stdout, "SERVER: Server received message: %s.\n", buf);fprintf(stdout, "SERVER: Respond to the client...\n");memset(buf, 0, buf_len);strcpy(buf, "hello from server");rc = send(client_fd, buf, buf_len, 0);if (rc == -1) {fprintf(stderr, "SERVER: fail to send:%s\n", strerror(errno));exit(1);}fprintf(stdout, "SERVER: Done!\n");close(server_sock);close(client_fd);remove(server_sock_path); // remove access to a file namedint status;auto pid2 = wait(&status); // system call suspends execution of the calling thread until one of its children terminatesfprintf(stdout, "process ID of the terminated child: %d\n", pid2);if (WIFEXITED(status)) { // returns true if the child terminated normallyfprintf(stdout, "child process ended with: exit(%d)\n", WEXITSTATUS(status));}if (WIFSIGNALED(status)) { // returns true if the child process was terminated by a signalfprintf(stderr, "child process ended with: kill -%d\n", WTERMSIG(status));}}if (pid == 0) { // client process(child process)int client_sock = socket(AF_UNIX, SOCK_STREAM, 0);if (client_sock == -1) {fprintf(stderr, "CLIENT: fail to socket: %s\n", strerror(errno));exit(1);}// bind client to an address on file system// Note: this binding could be skip if we want only send data to server without receivingstruct sockaddr_un client_addr;memset(&client_addr, 0, sizeof(client_addr));client_addr.sun_family = AF_UNIX;strcpy(client_addr.sun_path, client_sock_path);unlink (client_sock_path);auto rc = bind(client_sock, (struct sockaddr *)&client_addr, sizeof(client_addr));if (rc == -1) {fprintf(stderr, "CLIENT: fail to bind: %s\n", strerror(errno));exit(1);}// Set server address and connect to itstruct sockaddr_un server_addr;server_addr.sun_family = AF_UNIX;strcpy(server_addr.sun_path, server_sock_path);rc = connect(client_sock, (struct sockaddr*)&server_addr, sizeof(server_addr));if (rc == -1) {fprintf(stderr, "CLIENT: fail to connect: %s\n", strerror(errno));exit(1);}fprintf(stdout, "CLIENT: Connected to server.\n");// Send message to serverconst int buf_len = 256;char buf[buf_len];memset(buf, 0, buf_len);strcpy(buf, "hello from client");rc = send(client_sock, buf, buf_len, 0);if (rc == -1) {fprintf(stderr, "CLIENT: fail to send: %s\n", strerror(errno));exit(1);}fprintf(stdout, "CLIENT: Sent a message to server.\n");fprintf(stdout, "CLIENT: Wait for respond from server...\n");memset(buf, 0, buf_len);rc = recv(client_sock, buf, buf_len, 0);if (rc == -1) {fprintf(stderr, "CLIENT: fail to recv: %s\n", strerror(errno));exit(1);}elsefprintf(stdout, "CLIENT: Message received: %s\n", buf);fprintf(stdout, "CLIENT: Done!\n");close(client_sock);remove(client_sock_path);exit(0);}fprintf(stdout, "====== test finish ======\n");return 0;
}

编译脚本build.sh如下：

#! /bin/bashif [ -d build ]; thenecho "build directory already exists, it does not need to be created again"
elsemkdir -p build
ficd build
cmake ..
makerc=$?
if [[ ${rc} != 0 ]];thenecho "#### ERROR: please check ####"exit ${rc}
fiecho "==== build finish ===="

CMakeLists.txt内容如下：

cmake_minimum_required(VERSION 3.22)
project(samples_multi_process)set(CMAKE_BUILD_TYPE Release) # only works under linux
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -O2 -std=c++17")file(GLOB samples ${PROJECT_SOURCE_DIR}/test_*.cpp)
#message(STATUS "samples: ${samples}")foreach(sample ${samples})string(REGEX MATCH "[^/]+$" name ${sample})string(REPLACE ".cpp" "" exec_name ${name})#message(STATUS "exec name: ${exec_name}")add_executable(${exec_name} ${sample})target_link_libraries(${exec_name} rt)
endforeach()

执行结果如下所示：