1. semget创建/获取信号量

2. semop操作信号量，pv

3. semctl执行型号量命令，设置值、获取值、删除信号量等

锁一般用于线程间通信，进程间通信可以用信号量。还有其他的共享内存，消息队列，socket，管道等

模拟写了一个类似消费者/生产模式，消费者进程释放信号量，生产者进程获取信号量

//
// Created by gxf on 2020/2/23.
//

#ifndef UNTITLED_SEM_DEMO_H
#define UNTITLED_SEM_DEMO_H

extern char *ftokFilePath;
extern int projId;

extern int semId;

int initSem();
int semP();
int semV();
int delSem();

#endif //UNTITLED_SEM_DEMO_H

 

//
// Created by gxf on 2020/2/23.
//
#include "sem-demo.h"
#include <unistd.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <stdlib.h>
#include <stdio.h>

int semId;
char *ftokFilePath = "/Users/gxf/CLionProjects/untitled/tmp_sem_demo";
int projId = 1;

int initSem() {
    key_t  ftokRes = ftok(ftokFilePath, projId);
    // get sem
    semId = semget(ftokRes, 1, IPC_CREAT  | 0660);
    if (semId == -1) {
        perror("semget fail");
        return -1;
    }
    // init sem num 1
    union semun semunArg;
    semunArg.val = 1;
    int funRes = semctl(semId, 0, SETVAL, semunArg);
    if (funRes) {
        perror("semctl fail");
        return -1;
    }
    return 0;
}

int semP() {
    struct sembuf sembufVal;
    sembufVal.sem_num = 0;
    sembufVal.sem_op = -1;
    sembufVal.sem_flg = 0;
    int res = semop(semId, &sembufVal, 1);
    if (res) {
        perror("semop fail");
        return -1;
    }
    return 0;
}

int semV() {
    struct sembuf sembufVal;
    sembufVal.sem_op = 1;
    sembufVal.sem_num = 0;
    int res = semop(semId, &sembufVal, 1);
    if (res) {
        perror("semop fail");
        return -1;
    }
    return 0;
}

int delSem() {
    union semun semunVal;
    semId = 65544;
    int res = semctl(semId, 0, IPC_RMID, semunVal);
    if (res) {
        perror("semctl rmid fail");
        return -1;
    }
    return 1;
}

　　

//
// Created by gxf on 2020/2/23.
//

#include <stdio.h>
#include <stdlib.h>
#include "sem-demo.h"
#include <unistd.h>

int main() {
    initSem();
    while (1) {
        if (semV()) {
            printf("comsumer v fail\n");
        }
        printf("consumer\n");
        sleep(1);
    }

    return 0;
}

　　

 

//
// Created by gxf on 2020/2/23.
//

#include <stdio.h>
#include <stdlib.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <unistd.h>
#include "sem-demo.h"
#include <pthread.h>

void produce();

int main() {
//    delSem();
    initSem();
    pthread_t threads[10];
    for (int i = 0; i < 10; i++) {
        pthread_create(&threads[i], NULL, produce, NULL);
    }

    for (int i = 0; i < 10;i++) {
        pthread_join(threads[i], NULL);
    }

    return 0;
}

void produce() {
    while (1) {
        printf("producer tid:%d\n", pthread_self());
        semP();
//        sleep(3);
    }
}