linux共享内存与信号量的使用

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

static int init_semvalue (int);
static void del_semvalue (int);
static int P (int);
static int V (int);

//自己定义的semun结构体
union semun
{
int val;
struct semid_ds *buf;
unsigned short *array;
struct seminfo *__buf;
};

int
main (int argc, char *argv[])
{
int var_cri = 0;
int sem_id;
pid_t pid;

int *num;

//创建一个信号量
sem_id = semget ((key_t) 2234, 1, 0666 | IPC_CREAT);
//初始化一个信号量
if (!init_semvalue (sem_id))
{
fprintf (stderr, "Failed to initialize semaphore!\n");
exit (EXIT_FAILURE);
}
//创建子进程
if ((pid = fork ()) == 0) //子进程
{
int shid=shmget((key_t)654321,(size_t)4, 0600|IPC_CREAT);
if(shid==-1)
{
perror("shmget");
exit(EXIT_FAILURE);
}
num=shmat(shid, NULL,0);
if(num==NULL)
{
perror("shmat");
exit(EXIT_FAILURE);
}

while (1)
{
//临界区
if (!P (sem_id))//申请资源
exit (EXIT_FAILURE);
int i;
for (i = 0; i != 10; ++i)
{
(*num)++;
printf ("[child]: %d:%d\n", i,*num);
sleep (1);
}
if (!V (sem_id))//释放资源
exit (EXIT_FAILURE);
}
}
else if (pid > 0)      //父进程
{
int shid=shmget((key_t)654321,(size_t)4, 0600|IPC_CREAT);
if(shid==-1)
{
perror("shmget");
exit(EXIT_FAILURE);
}
num=shmat(shid, NULL,0);
if(num==NULL)
{
perror("shmat");
exit(EXIT_FAILURE);
}
sleep (1);
while (1)
{
//临界区
if (!P (sem_id))
exit (EXIT_FAILURE);
int i;
for (i = 0; i != 10; ++i)
{
(*num)++;
printf ("[parent]: %d:%d\n", i,*num);
sleep (1);
}
if (!V (sem_id))
exit (EXIT_FAILURE);
}
sleep (8);
//销毁信号量
del_semvalue (sem_id);
}
exit (EXIT_SUCCESS);
}

static int
init_semvalue (int id)
{
union semun sem_union;
sem_union.val = 1;
if (semctl (id, 0, SETVAL, sem_union) == -1)//设置信号量集中的信号量值value
return (0);
return (1);
}

static void
del_semvalue (int id)
{
union semun sem_union;
if (semctl (id, 0, IPC_RMID, sem_union) == -1)//IPC——RMID将信号量集从内存中删除
fprintf (stderr, "Failed to delete semaphore\n");
}

int
P (int id)
{
struct sembuf op;

op.sem_num = 0;//单信号
op.sem_op = -1;//P操作
op.sem_flg = 0;
if (semop (id, &op, 1) < 0)//改变key,它代表进程要使用的某个资源
return 0;
return 1;
}

int
V (int id)
{
struct sembuf op;

op.sem_num = 0;
op.sem_op = 1;//V操作
op.sem_flg = 0;
if (semop (id, &op, 1) < 0)
return 0;
return 1;
}