linux编程---信号量通信机制

来源：互联网发布：linux ftp更改下载目录编辑：程序博客网时间：2024/06/05 11:27

信号量通信机制主要用来实现进程间同步，信号量用来标识系统可用资源的个数。

信号量管理操作

1. 创建信号量集合

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>

int semget(key_t key, int nsems, int semflg);

2. 控制信号量集合、信号量

int semctl(int semid, int semnum, int cmd, ...);

3. 信号量操作

int semop(int semid, struct sembuf *sops, unsigned nsops);

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

static int semaphore_v(void);
static int set_semvalue(void);
static int get_semvalue(void);

union semun
{
   int val;
   struct semid_ds* buf;
   unsigned short int* array;
   struct seminfo* __buf;
};

int sem_id;

int main(int argc,char* argv[])
{
   pid_t pid;
   int i;
   int value;
   key_t key;
   int status;

   if((key = ftok(".",'B')) == -1)
   perror("ftok ");

   if((pid = fork()) == -1)
   {
       perror("fork ");
       exit(-1);
   }
   else if(pid == 0)
   {
       if((sem_id = semget(key,1,IPC_CREAT|0777)) == -1)
           perror("semget ");
       if(!set_semvalue())
           fprintf(stderr,"failed to initialize semphore\n");
       value = get_semvalue();
       printf("this is child,the current value is %d\n",value);

       if(!semaphore_v())
           fprintf(stderr,"failed to v operator\n");
       value = get_semvalue();
       printf("the child %d V operator,value %d \n",i,value);

       printf("child exit sucess\n");
       exit(0);
   }
   else{
   sleep(3);
   if((sem_id = semget(key,1,IPC_CREAT|0777)) == -1)
       perror("semget ");

   value = get_semvalue();
   printf("this is parent,the current value is %d\n",value);
   printf("the parent will remove the sem\n");
   if(semctl(sem_id,0,IPC_RMID,(struct msquid_ds*)0) == -1)
       perror("semctl");

   return 0;
   }
}

static int set_semvalue(void )
{
   union semun sem_union;
   int value;
   sem_union.val = 5;
   if(semctl(sem_id,0,SETVAL,sem_union) == -1)
       return 0;
   printf("set value success,");
   printf("init value is %d\n",get_semvalue());
}

static int get_semvalue(void)
{
   int res;
   if((res = semctl(sem_id,0,GETVAL)) == -1)
       perror("semctl");

   return res;
}

static int semaphore_v(void)
{
   struct sembuf sem_b;
   sem_b.sem_num = 0;
   //sem_b.sem_op = 1; //V
   sem_b.sem_op = -2; //P
   //sem_b.sem_flg = 0;
   sem_b.sem_flg = SEM_UNDO;
   if(semop(sem_id,&sem_b,1) == -1)
       perror("semop ");
   return 1;
}

生产者与消费者问题

生产者代码

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

int sem_id;

void init()
{
        key_t key;
        int ret;
        unsigned short sem_array[2];
        union semun
        {
                int val;
                struct semid_ds* buf;
                unsigned short* array;
        }arg;

        key = ftok(".",'s');
        sem_id = semget(key,2,IPC_CREAT|0644);
        sem_array[0] = 0;
        sem_array[1] = 100;
        arg.array = sem_array;
        ret = semctl(sem_id,0,SETALL,arg);
        if(ret == -1)
                perror("semctl ");

        printf("productor init is %d\n",semctl(sem_id,0,GETVAL));
        printf("space init is %d\n",semctl(sem_id,1,GETVAL));
}

void del()
{
        semctl(sem_id,IPC_RMID,0);
}

int main(int argc,char* argv[])
{
        struct sembuf sops[2];
        sops[0].sem_num = 0;
        sops[0].sem_op = 1;
        sops[0].sem_flg = 0;

        sops[1].sem_num = 1;
        sops[1].sem_op = -1;
        sops[1].sem_flg = 0;

        init();
        printf("this is productor\n");

        while(1)
        {
                printf("\n\nbefore produce:\n");
                printf("productor number is %d\n",semctl(sem_id,0,GETVAL));
                printf("space number is %d\n",semctl(sem_id,1,GETVAL));
                semop(sem_id,(struct sembuf*)&sops[1],1);
                printf("now producing ...\n");
                semop(sem_id,(struct sembbuf*)&sops[0],1);

                printf("\nafter produce\n");
                printf("productor number is %d\n",semctl(sem_id,0,GETVAL));
                printf("space number is %d\n",semctl(sem_id,1,GETVAL));
                sleep(4);
        }
        del();
}

消费者代码

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

int sem_id;

void init()
{
        key_t key;
        int ret;
        unsigned short sem_array[2];
        union semun
        {
                int val;
                struct semid_ds* buf;
                unsigned short* array;
        }arg;

        key = ftok(".",'s');
        sem_id = semget(key,2,IPC_CREAT|0644);
}

int main(int argc,char* argv[])
{
        init();
        struct sembuf sops[2];
        sops[0].sem_num = 0;
        sops[0].sem_op = -1;
        sops[0].sem_flg = 0;

        sops[1].sem_num = 1;
        sops[1].sem_op = 1;
        sops[1].sem_flg = 0;

        //init();
        printf("this is customer\n");

        while(1)
        {
                printf("\n\nbefore consume:\n");
                printf("productor number is %d\n",semctl(sem_id,0,GETVAL));
                printf("space number is %d\n",semctl(sem_id,1,GETVAL));
                semop(sem_id,(struct sembuf*)&sops[0],1);
                printf("now consuming ...\n");
                semop(sem_id,(struct sembbuf*)&sops[1],1);

                printf("\nafter consume\n");
                printf("productor number is %d\n",semctl(sem_id,0,GETVAL));
                printf("space number is %d\n",semctl(sem_id,1,GETVAL));
                sleep(3);
        }
}

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