POSIX和system v

Both POSIX and system v are protocols applied to the system, and POSIX IPC and system v IPC can be used for inter-process communication

1. The difference in functions: System V function names do not have underscores, POSIX function names have underscores

2. The way to operate the semaphore:

POSIX IPC: Use sem_wait() to subtract 1 from the semaphore, and sem_post() to increase the semaphore by 1

system V: Use a semget () Get semaphore identifier, for sembuf provided, a semop () using the signal

3. POSIX unnamed semaphore can put data into shared memory for inter-process communication

4. System v semaphore has id

the difference

System V semaphore and Posix semaphore

system v adds 1 code to the semaphore

/*对信号量加一*/
void sem_v(int semid)
{
    struct sembuf sops = {0,1,0};//默认阻塞
     int ret = semop(semid,&sops, 1);
     if (ret == -1)
     {
         perror("");
     }
}

system p implements the reduction of 1 code for the semaphore

//对信号量减1
void sem_p(int semid)
{
    struct sembuf sops = { 0,-1,0 };//默认阻塞
    int ret = semop(semid, &sops, 1);
    if (ret == -1)
    {
        perror("");
    }
}

The following external operations on the semaphore minus 1 (to obtain the semaphore identifier externally, call the custom sem_p(), sem_v() functions to operate on the signal set)

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <iostream>
#include <sys/shm.h>
#include <errno.h>
#include <stdio.h>
#include <unistd.h>
using namespace std;

int main()
{
    int semid = semget(1234, 0, 0);// get a System V semaphore set identifier
    if (semid == -1)
    {
       
        semid = semget(1234, 1, IPC_CREAT | 0666);//打开失败创建
    }

    sem_p(semid2);
    return 0;
}

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