c信号量操作demo
#include <stdio.h>#include <string.h>
#include <sys/ipc.h>
#include <sys/sem.h>
// union semun {
// int val;
// struct semid_ds *buf;
// unsigned short *array;
// struct seminfo *__buf;
// };
int P(int semid, int semnum) {
struct sembuf sops={semnum, -1, SEM_UNDO};
return (semop(semid, &sops, 1));
}
int V(int semid, int semnum) {
struct sembuf sops = {semnum, +1, SEM_UNDO};
return (semop(semid, &sops, 1));
}
void test2();
int main(int argc, char **argv){
printf("argc:%d, argv:%s\n", argc, *argv);
test2();
return 0;
}
void test2(){
int key;
int semid,ret;
union semun arg;
struct sembuf semop;
int flag;
key = ftok("/tmp", 0x66);
arg.val = 3;
if (key < 0) {
perror("ftok key error");
}
semid = semget(key, 3, IPC_CREAT | 0600);
if(semid == -1) {
perror("create semget error");
}
//对0号信号量设置为初始值
ret = semctl(semid, 0, SETVAL, arg);
printf("ret:%d\n", ret);
if(ret < 0) {
perror("ctl sem error");
semctl(semid, 0, IPC_RMID, arg);
}
//取0号信号量的值
ret = semctl(semid, 0, GETVAL, arg);
printf("after semctl setval sem.val=[%d]\n", ret);
//P操作
flag = P(semid, 0);
flag = P(semid, 0);
ret = semctl(semid, 0, GETVAL, arg);
printf("after P sem.val=[%d]\n",ret);
//V操作
if (V(semid, 0) < 0) {
perror("V operator error");
}
if (V(semid, 0) < 0) {
perror("V operator error");
}
ret = semctl(semid, 0, GETVAL, arg);
printf("after v 操作 sem.val=%d\n", ret);
}
文档来源：51CTO技术博客https://blog.51cto.com/u_2498536/3304171
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