linux进程通信（四）--共享内存+信号量

   1. /*server.c:向共享内存中写入People*/  
   2. #include <stdio.h>  
   3. #include <sys/types.h>  
   4. #include <sys/ipc.h>  
   5. #include <sys/sem.h>  
   6.   
   7. int main()  
   8. {  
   9.     struct People{  
  10.         char name[10];  
  11.         int age;  
  12.     };  
  13.       
  14.     int semid;  
  15.     int shmid;  
  16.     key_t semkey;  
  17.     key_t shmkey;  
  18.     semkey=ftok("server.c",0);  
  19.     shmkey=ftok("client.c",0);  
  20.       
  21.     /*创建共享内存和信号量的IPC*/  
  22.     semid=semget(semkey,1,0666|IPC_CREAT);  
  23.     if(semid==-1)  
  24.     printf("creat sem is fail\n");  
  25.     shmid=shmget(shmkey,1024,0666|IPC_CREAT);  
  26.     if(shmid==-1)  
  27.     printf("creat shm is fail\n");  
  28.       
  29.     /*设置信号量的初始值，就是资源个数*/  
  30.     union semun{  
  31.         int val;  
  32.         struct semid_ds *buf;  
  33.         ushort *array;  
  34.     }sem_u;  
  35.       
  36.     sem_u.val=1;  
  37.     semctl(semid,0,SETVAL,sem_u);  
  38.       
  39.     /*将共享内存映射到当前进程的地址中，之后直接对进程中的地址addr操作就是对共享内存操作*/  
  40.       
  41.     struct People * addr;  
  42.     addr=(struct People*)shmat(shmid,0,0);  
  43.     if(addr==(struct People*)-1)  
  44.     printf("shm shmat is fail\n");  
  45.       
  46.     /*信号量的P操作*/  
  47.     void p()  
  48.     {  
  49.         struct sembuf sem_p;  
  50.         sem_p.sem_num=0;  
  51.         sem_p.sem_op=-1;  
  52.         if(semop(semid,&sem_p,1)==-1)  
  53.         printf("p operation is fail\n");          
  54.     }  
  55.   
  56.     /*信号量的V操作*/  
  57.     void v()  
  58.     {  
  59.         struct sembuf sem_v;  
  60.         sem_v.sem_num=0;  
  61.         sem_v.sem_op=1;  
  62.         if(semop(semid,&sem_v,1)==-1)  
  63.         printf("v operation is fail\n");  
  64.     }  
  65.       
  66.     /*向共享内存写入数据*/  
  67.     p();  
  68.     strcpy((*addr).name,"xiaoming");  
  69. /* 注意：①此处只能给指针指向的地址直接赋值，不能在定义一个  struct People people_1;addr=&people_1; 因为addr在addr=(struct People*)shmat(shmid,0,0);时,已经由系统自动分配了一个地址，这个地址与共享内存相关联，所以不能改变这个指针的指向，否则他将不指向共享内存，无法完成通信了。 
  70. 注意：②给字符数组赋值的方法。刚才太虎了。。*/  
  71.     (*addr).age=10;  
  72.     v();  
  73.       
  74.     /*将共享内存与当前进程断开*/  
  75.     if(shmdt(addr)==-1)  
  76.     printf("shmdt is fail\n");    
  77.       
  78. }  

   1. /*client.c:从共享内存中读出People*/  
   2. #include <stdio.h>  
   3. #include <sys/types.h>  
   4. #include <sys/ipc.h>  
   5. #include <sys/sem.h>  
   6.   
   7. int main()  
   8. {  
   9.     int semid;  
  10.     int shmid;  
  11.     key_t semkey;  
  12.     key_t shmkey;  
  13.     semkey=ftok("server.c",0);  
  14.     shmkey=ftok("client.c",0);  
  15.       
  16.     struct People{  
  17.         char name[10];  
  18.         int age;  
  19.     };  
  20.   
  21.     /*读取共享内存和信号量的IPC*/    
  22.     semid=semget(semkey,0,0666);  
  23.     if(semid==-1)  
  24.     printf("creat sem is fail\n");  
  25.     shmid=shmget(shmkey,0,0666);  
  26.     if(shmid==-1)  
  27.     printf("creat shm is fail\n");  
  28.       
  29.     /*将共享内存映射到当前进程的地址中，之后直接对进程中的地址addr操作就是对共享内存操作*/  
  30.     struct People * addr;  
  31.     addr=(struct People*)shmat(shmid,0,0);  
  32.     if(addr==(struct People*)-1)  
  33.     printf("shm shmat is fail\n");  
  34.       
  35.     /*信号量的P操作*/  
  36.     void p()  
  37.     {  
  38.         struct sembuf sem_p;  
  39.         sem_p.sem_num=0;  
  40.         sem_p.sem_op=-1;  
  41.         if(semop(semid,&sem_p,1)==-1)  
  42.         printf("p operation is fail\n");          
  43.     }  
  44.       
  45.     /*信号量的V操作*/  
  46.     void v()  
  47.     {  
  48.         struct sembuf sem_v;  
  49.         sem_v.sem_num=0;  
  50.         sem_v.sem_op=1;  
  51.         if(semop(semid,&sem_v,1)==-1)  
  52.         printf("v operation is fail\n");  
  53.     }  
  54.       
  55.     /*从共享内存读出数据*/  
  56.     p();  
  57.     printf("name:%s\n",addr->name);  
  58.     printf("age:%d\n",addr->age);  
  59.     v();  
  60.       
  61.     /*将共享内存与当前进程断开*/  
  62.     if(shmdt(addr)==-1)  
  63.     printf("shmdt is fail\n");  
  64.       
  65.     /*IPC必须显示删除。否则会一直留存在系统中*/  
  66.     if(semctl(semid,0,IPC_RMID,0)==-1)  
  67.     printf("semctl delete error\n");  
  68.     if(shmctl(shmid,IPC_RMID,NULL)==-1)  
  69.     printf("shmctl delete error\n");  
  70. }