使用system V实现读者写者问题

  1 #include <stdio.h>
  2 #include <sys/sem.h>
  3 #include <sys/ipc.h>
  4 #include <string.h>
  5 #include <errno.h>
  6 #include <unistd.h>
  7 #include <pthread.h>
  8 #include <sys/types.h>
  9 #include <sys/wait.h>
 10 
 11 typedef int semophore;
 12 //semophore mutex = 1;
 13 semophore cnt = 0;
 14 //semophore db = 1;
 15 char mutex[] = "mutex";
 16 char db[] = "db";
 17 int semId;
 18 void read(int cnt)
 19 {
 20     fprintf(stdout, "NO.%d reading...\n",cnt);
 21     //for (int i = 0; i < 1000000; i++);
 22     sleep(1);
 23     fprintf(stdout, "NO.%d read finished.\n",cnt);
 24 
 25 }
 26 void write()
 27 {
 28     fprintf(stdout, "writing...\n");
 29     //for (int i = 0; i < 1000000; i++);
 30     sleep(1);
 31     fprintf(stdout, "write finished.\n");
 32 }
 33 
 34 union semun {
 35     int val;
 36     struct semid_ds *buf;
 37     unsigned short int *array;
 38     struct seminfo *__buf;
 39 };
 40 
 41 void p(const char *s)
 42 {
 43     semun arg;
 44     int tmp;
 45     int r;
 46     if (strcmp(s, mutex) == 0)
 47     {
 48         //fprintf(stdout,"mutex:%d\n",semctl(semId, 0, GETVAL, arg));
 49         while(1){
 50             if(semctl(semId, 0, GETVAL, arg)<=0)
 51                 wait(&r);
 52             else break;
 53         }
 54         tmp = semctl(semId, 0, GETVAL, arg);
 55         //if(tmp<=0) waitpid();
 56         arg.val = tmp - 1;
 57         semctl(semId, 0, SETVAL, arg);
 58     }
 59     else if (strcmp(s, db) == 0)
 60     {
 61         //fprintf(stdout,"db:%d\n",semctl(semId, 1, GETVAL, arg));
 62         while(1){
 63             if(semctl(semId, 1, GETVAL, arg)<=0)
 64                 wait(&r);
 65             else break;
 66         }
 67         tmp = semctl(semId, 1, GETVAL, arg);
 68         arg.val = tmp - 1;
 69         semctl(semId, 1, SETVAL, arg);
 70     }
 71 }
 72 void v(const char *s)
 73 {
 74     semun arg;
 75     int tmp;
 76     if (strcmp(s, mutex) == 0)
 77     {
 78         tmp = semctl(semId, 0, GETVAL, arg);
 79         arg.val = tmp + 1;
 80         semctl(semId, 0, SETVAL, arg);
 81     }
 82     else if (strcmp(s, db) == 0)
 83     {
 84         tmp = semctl(semId, 1, GETVAL, arg);
 85         arg.val = tmp + 1;
 86         semctl(semId, 1, SETVAL, arg);
 87     }
 88 }
 89 
 90 void* reader(void* args)
 91 {
 92     p(mutex);
 93     cnt++;
 94     if (cnt == 1)
 95     {
 96         p(db);
 97     }
 98     v(mutex);
 99 
100     read(cnt);
101 
102     p(mutex);
103     cnt--;
104     if (cnt == 0)
105     {
106         v(db);
107     }
108     v(mutex);
109 }
110 void* writer(void* args)
111 {
112     p(db);
113     write();
114     v(db);
115 }
116 
117 int main()
118 {
119     semun arg;
120     if ((semId = semget(1, 2, IPC_CREAT | IPC_EXCL | 0666)) >= 0)
121     {
122         arg.val = 1;
123         if (semctl(semId, 0, SETALL, arg) < 0)
124         {
125             fprintf(stdout, "semctl error %s\n", strerror(errno));
126             return -1;
127         }
128 
129     }
130     else if (errno == EEXIST)
131     {
132         semId = semget(1, 2, 0666);
133     }
134     else
135     {
136         fprintf(stdout, "semget error %s\n", strerror(errno));
137         return -1;
138     }
139     pthread_t tids[5];
140     for(int i = 0; i < 5; ++i)
141     {
142         //fprintf(stdout,"turn NO.%d\n",i);
143         //参数依次是：创建的线程id，线程参数，调用的函数，传入的函数参数
144         if(i==0 || i==2 || i==4)
145         {
146             int ret = pthread_create(&tids[i], NULL, reader, NULL);
147             if (ret != 0)
148             {
149                 fprintf(stdout, "reading error\n");
150             }
151         }
152         else{
153             int ret = pthread_create(&tids[i], NULL, writer, NULL);
154             if (ret != 0)
155             {
156                 fprintf(stdout, "writing error\n");
157             }
158         }
159     }
160 
161     pthread_exit(NULL);
162     return 0;
163 }