Inter-process communication-message transmission (Message Queue)

[Statement: This article is only intended for self-Summary and mutual communication, and may be omitted. Contact Email: Mr_chenping@163.com message queue is the list of messages. We can think of it as a linked list queue. Users can add or read messages from messages. In this way, it has the FIFO feature, but it can implement random query of messages, therefore, MQ has a greater advantage than FIFO. Message Queues exist in the kernel and are identified by queue IDs. Message Queue features: 1. It can be used in kinship processes (threads) and non-kinship processes (threads. 2. data can be accessed sequentially and randomly. 3. The System V Message Queue continues with the kernel. It is deleted only when the kernel restarts or explicitly deletes a message queue. The following two Code demonstrates the function: server. c: Creates a message queue, obtains the input content on the keyboard, and then writes it to the message queue. Client. c: Open the Message Queue created by server. c, read the content in the message queue, and display it on the screen. Server: [cpp] # include <sys/types. h> # include <sys/ipc. h> # include <sys/msg. h> # include <stdio. h> # include <stdlib. h> # include <unistd. h> # include <string. h> # include <string. h ># define BUFFER_SIZE 512 struct message {long msg_type; char msg_text [BUFFER_SIZE] ;}; int main () {int qid; key_t key; struct message msg; /* generate a standard key */if (key = ftok (". ", 512) =-1) {perror (" ftok "); exit (1);}/* Create A Message Queue */if (qid = msgget (key, IPC_CREAT | 0666) =-1) {perror ("msgget"); exit (1);} printf ("Open queue % d \ n", qid ); while (1) {printf ("input some message to the queue:"); if (fgets (msg. msg_text, BUFFER_SIZE, stdin) = NULL) {puts ("no message"); exit (1);} msg. msg_type = getpid ();/* Add a message to the Message Queue */if (msgsnd (qid, & msg, strlen (msg. msg_text), 0) <0) {perror ("message posted"); exit (1);} if (strncmp (msg. msg_text, "quit", 4) = 0) {break ;}} exit (0);} customer service end: [cpp] # include <sys/types. h> # include <sys/ipc. h> # include <sys/msg. h> # include <stdio. h> # include <stdlib. h> # include <unistd. h> # include <string. h> # include <string. h ># define BUFFER_SIZE 512 struct message {long msg_tpye; char msg_text [BUFFER_SIZE] ;}; int main () {int qid; key_t key; struct message msg; /* generate a standard key */if (key = ftok (". ", 512) =-1) {perror (" ftok "); exit (1);} if (qid = msgget (key, IPC_CREAT | 0666 )) <0) {perror ("msgget"); exit (1);} printf ("Open queue % d \ n", qid); do {memset (msg. msg_text, 0, BUFFER_SIZE); if (msgrcv (qid, (void *) & msg, BUFFER_SIZE, 0, 0) <0) {perror ("msgrcv "); exit (1);} printf ("The message form process % d: % s", msg. msg_tpye, msg. msg_text);} while (strncmp (msg. msg_text, "quit", 4); if (msgctl (qid, IPC_RMID, NULL) <0) {perror ("msgctl"); exit (1 );} exit (0 );}