# linux ipc

很讚的筆記https://jasonblog.github.io/note/linux_system/linux_xia_ipc_de_yun_zuo_fang_shi.html
https://hackmd.io/@sysprog/linux-shared-memory
https://yayaya6d.pixnet.net/blog/post/350095123-linus%E5%90%84%E7%A8%AE%E9%9B%9C%E8%AB%87--process%E9%96%93%E7%9A%84%E6%BA%9D%E9%80%9A%EF%BC%9Amsg-queue

## shard_memory
### server

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <stdio.h>

#define SHMSZ     27

int main()
{
    char c;
    int shmid;
    key_t key;
    char* shm, *s;

    /*
     * We'll name our shared memory segment
     * "5678".
     */
    key = 5678;

    /*
     * Create the segment.
     */
    if ((shmid = shmget(key, SHMSZ, IPC_CREAT | 0666)) < 0) {
        perror("shmget");
        exit(1);
    }

    /*
     * Now we attach the segment to our data space.
     */
    if ((shm = shmat(shmid, NULL, 0)) == (char*) - 1) {
        perror("shmat");
        exit(1);
    }

    /*
     * Now put some things into the memory for the
     * other process to read.
     */
    s = shm;

    for (c = 'a'; c <= 'z'; c++) {
        *s++ = c;
    }

    *s = NULL;

    /*
     * Finally, we wait until the other process
     * changes the first character of our memory
     * to '*', indicating that it has read what
     * we put there.
     */
    while (*shm != '*') {
        sleep(1);
    }

    exit(0);
}

### client

/*
 * shm-client - client program to demonstrate shared memory.
 */
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <stdio.h>

#define SHMSZ     27

main()
{
    int shmid;
    key_t key;
    char* shm, *s;

    /*
     * We need to get the segment named
     * "5678", created by the server.
     */
    key = 5678;

    /*
     * Locate the segment.
     */
    if ((shmid = shmget(key, SHMSZ, 0666)) < 0) {
        perror("shmget");
        exit(1);
    }

    /*
     * Now we attach the segment to our data space.
     */
    if ((shm = shmat(shmid, NULL, 0)) == (char*) - 1) {
        perror("shmat");
        exit(1);
    }

    /*
     * Now read what the server put in the memory.
     */
    for (s = shm; *s != NULL; s++) {
        putchar(*s);
    }

    putchar('\n');

    /*
     * Finally, change the first character of the
     * segment to '*', indicating we have read
     * the segment.
     */
    *shm = '*';

    exit(0);
}

root@HOME-X213212:~/leetcode-1# ipcs

------ Message Queues --------
key        msqid      owner      perms      used-bytes   messages    

------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status      
0x0000162e 0          root       666        27         0                       

------ Semaphore Arrays --------
key        semid      owner      perms      nsems     

./client
root@HOME-X213212:~/leetcode-1/ipc/shardmemory# ./client 
*bcdefghijklmnopqrstuvwxyz

## message queue
### server

#include <stdio.h>
#include <stdlib.h>
#include <sys/msg.h>

// 用于创建一个唯一的key
#define MSG_FILE "/etc/passwd"

// 消息结构
struct msg_form {
	long mtype;
	char mtext[256];
};

int main()
{
	int msqid;
	key_t key;
	struct msg_form msg;
	
	// 获取key值
	if((key = ftok(MSG_FILE,'z')) < 0)
	{
		perror("ftok error");
		exit(1);
	}

	// 打印key值
	printf("Message Queue - Server key is: %d.\n", key);

	// 创建消息队列
	if ((msqid = msgget(key, IPC_CREAT|0777)) == -1)
	{
		perror("msgget error");
		exit(1);
	}

	// 打印消息队列ID及进程ID
	printf("My msqid is: %d.\n", msqid);
	printf("My pid is: %d.\n", getpid());

	// 循环读取消息
	for(;;) 
	{
		msgrcv(msqid, &msg, 256, 888, 0);// 返回类型为888的第一个消息
		printf("Server: receive msg.mtext is: %s.\n", msg.mtext);
		printf("Server: receive msg.mtype is: %d.\n", msg.mtype);

		msg.mtype = 999; // 客户端接收的消息类型
		sprintf(msg.mtext, "hello, I'm server %d", getpid());
		msgsnd(msqid, &msg, sizeof(msg.mtext), 0);
	}
	return 0;
}

### client

#include <stdio.h>
#include <stdlib.h>
#include <sys/msg.h>

// 用于创建一个唯一的key
#define MSG_FILE "/etc/passwd"

// 消息结构
struct msg_form {
	long mtype;
	char mtext[256];
};

int main()
{
	int msqid;
	key_t key;
	struct msg_form msg;

	// 获取key值
	if ((key = ftok(MSG_FILE, 'z')) < 0) 
	{
		perror("ftok error");
		exit(1);
	}

	// 打印key值
	printf("Message Queue - Client key is: %d.\n", key);

	// 打开消息队列
	if ((msqid = msgget(key, IPC_CREAT|0777)) == -1) 
	{
		perror("msgget error");
		exit(1);
	}

	// 打印消息队列ID及进程ID
    printf("My msqid is: %d.\n", msqid);
	printf("My pid is: %d.\n", getpid());

	// 添加消息，类型为888
	msg.mtype = 888;
	sprintf(msg.mtext, "hello, I'm client %d", getpid());
	msgsnd(msqid, &msg, sizeof(msg.mtext), 0);

	// 读取类型为777的消息
	msgrcv(msqid, &msg, 256, 999, 0);
	printf("Client: receive msg.mtext is: %s.\n", msg.mtext);
	printf("Client: receive msg.mtype is: %d.\n", msg.mtype);
	return 0;
}

------ Message Queues --------
key        msqid      owner      perms      used-bytes   messages    
0x7a202919 0          root       777        0            0           

------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status      
0x0000162e 0          root       666        27         0                       

------ Semaphore Arrays --------
key        semid      owner      perms      nsems     

server

root@HOME-X213212:~/leetcode-1/ipc/messagequeue# ./server 
Message Queue - Server key is: 2048928025.
My msqid is: 0.
My pid is: 17918.
Server: receive msg.mtext is: hello, I'm client 17946.
Server: receive msg.mtype is: 888.

client

root@HOME-X213212:~/leetcode-1/ipc/messagequeue# ./client 
Message Queue - Client key is: 2048928025.
My msqid is: 0.
My pid is: 17946.
Client: receive msg.mtext is: hello, I'm server 17918.
Client: receive msg.mtype is: 999.