1 #include<sys/types.h>
  2 #include<sys/ipc.h>
  3 #include<sys/sem.h>
  4 #include <stdio.h>
  5 #include <stdlib.h>
  6 #include<errno.h>
  7 
  8 int gSemid = 0;
  9 typedef int sem_t;
 10 #define ERR_EXIT(m) \
 11         do \
 12         { \
 13             perror(m); \
 
 14             exit(EXIT_FAILURE); \
 15         }while(0)
 16 
 17 sem_t CreateSem(key_t key, int value)
 18 {
 19     union semun sem;
 20     sem_t semid;
 21     sem.val = value;
 22 
 23     semid = semget(key, 1, IPC_CREAT | IPC_EXCL | 0666);//建立訊號量個數為1
 24     if(-1 == semid)
 25     {
 26         ERR_EXIT("
 
semget");
 27     }
 28     semctl(semid, 0, SETVAL, sem);//引數2-要操作的訊號量在訊號量集中的編號；引數3-cmd...
 29     
 30     return semid;
 31 }
 32 
 33 int Sem_P(sem_t semid)
 34 {
 35     //sops有三種方式，0-預設阻塞、IPC_NOWAIT-非阻塞、SEM_UNDO-撤銷上一次操作
 36     struct sembuf sops={0,-1,0};
 37     return (semop(semid,&sops,1));
 38
 
 }
 39 
 40 int Sem_V(sem_t semid)
 41 {
 42     struct sembuf sops={0,+1,0};
 43     return (semop(semid,&sops,1));
 44 }
 45 
 46 void SetvalueSem(sem_t semid, int value)
 47 {
 48     union semun sem;
 49     sem.val = value;
 50     
 51     semctl(semid,0,SETVAL,sem);
 52 }
 53 
 54 int GetvalueSem(sem_t semid)
 55 {
 56     union semun sem;
 57     return semctl(semid,0,GETVAL,sem);
 58 }
 59 
 60 void DestroySem(sem_t semid)
 61 {
 62     union semun sem;
 63     sem.val = 0;
 64     semctl(semid,0,IPC_RMID,sem);
 65 }
 66 
 67 void Print(char opChar)
 68 {
 69     int pauseTime;
 70     srand(getpid());
 71     int i;
 72 
 73     for(i=0; i<10; i++)
 74     {
 75         if(Sem_P(gSemid) != 0)
 76             ERR_EXIT("Sem_P");
 77         //臨界區-begin
 78         printf("%c", opChar);
 79         fflush(stdout);
 80         pauseTime = rand()%3;
 81         sleep(pauseTime);
 82         printf("%c", opChar);
 83         fflush(stdout);
 84         //臨界區-end
 85         Sem_V(gSemid);
 86         pauseTime = rand()%2;
 87         sleep(pauseTime);
 88     }
 89 }
 90 
 91 int main(void)
 92 {
 93     char i;
 94     key_t key;
 95     int value = 0;
 96     int pid;
 97         
 98     key = ftok("./ipc", 'c');
 99     gSemid = CreateSem(key,1);
100 
101     value = GetvalueSem(gSemid);
102     printf("訊號量值 = %d\n",value);
103 
104     pid = fork();
105     if(-1 == pid)
106     {
107         ERR_EXIT("fork");
108     }
109 
110     if(pid > 0)//父程序
111     {
112         Print('o');
113         wait(NULL);//等待子程序推出，刪除訊號量集
114         DestroySem(gSemid);
115     }else//子程序
116     {
117         Print('x');
118     }
119     
120 #if 0
121     for(i = 0; i<105; i++)
122     {
123         if(Sem_P(gSemid) != 0)
124             ERR_EXIT("Sem_P");
125 
126         value = GetvalueSem(gSemid);
127         printf("訊號量值 = %d\n",value);
128         
129         Sem_V(gSemid);
130         //value = GetvalueSem(semid);
131         //printf("訊號量值 = %d\n",value);
132     }
133 #endif    
134     
135     return 0;
136 }