Eating fruit

Father feeds fruit to his daughter and son . Dad randomly selects oranges or apples and puts them on the plate . My daughter only eats oranges , My son only eats apples . The plate can hold 2 Fruit . Use semaphores to coordinate processes , Print to show that you have eaten the corresponding fruit
Topic analysis

This is a classic communication problem between processes
Dad randomly put the fruit on the plate , It can be abstracted as a producer ,
daughter , Son eats fruit , It can be understood as two consumers , What is special is , Two consumers will only consume the specified products
So we can define three processes , Namely ： producer , Consumer one , Consumer number two .
The content in the process can be defined as ： Producers produce 0 or 1, Consumer one will only consume 1, Consumer number two will only consume 0.
The above is the main code framework , Next is PV operation , According to the number of producers and consumers , We define 4 A semaphore , Respectively used to control producers , consumer 1, consumer 2, And the control signal written to the cache , The semaphore corresponding to the producer and buffer should be initialized to 1, Only in this way can we ensure that the process can proceed normally , And it can block normally . For the other 0, Of course, this is to let producers produce first , According to normal logic , You set one of the consumers to 1, It can also run
After arranging the semaphore reasonably , You need to create a shared memory , It just needs to open up a space , To ensure that the three processes can read or input the corresponding values in memory .
The above is the general idea , As for function and code calls , Baidu .

Code implementation

#include<unistd.h>
#include<stdlib.h>
#include<sys/types.h>
#include<sys/ipc.h>
#include <sys/shm.h>
#include<stdio.h>
#include <sys/sem.h>
union semun
 {
    int val;
    struct semid_ds *buf;
    unsigned short *arry;
  };
int main()
{	
int semid1 =  semget((key_t)1234, 1 , 0640|IPC_CREAT);
union semun sem_union1;
sem_union1.val = 1;
semctl(semid1,0,SETVAL,sem_union1);
struct sembuf sem_b;
int semid2 =  semget((key_t)1235, 1 , 0640|IPC_CREAT);
union semun sem_union2;
sem_union2.val = 0;
semctl(semid2,0,SETVAL,sem_union2);
struct sembuf sem_a;
int semid3 = semget ((key_t)1111,1, 0640|IPC_CREAT);
union semun sem_union3;
em_union3.val = 0;
semctl(semid3,0,SETVAL,sem_union3);
struct sembuf sem_c ;
int semid4  = semget((key_t)1110,1,0640|IPC_CREAT);
union semun sem_union4;
sem_union4.val = 1semctl(semid4, 0, SETVAL,sem_union4);
struct sembuf sem_d   ;
	
int shmid = shmget(IPC_PRIVATE  , 2, 0640|IPC_CREAT);
        if(shmid <0)
        {
        printf("error!");
	    } 
char *ptext = 0 ;
ptext  = (char*)shmat(shmid,0,0);
pid_t pa = 0;
pa = fork();
if(pa<0)
{	
		printf("erorr!");
}
else if (pa==0)
{
        	pid_t pb = 0;
        	pb = fork();
        	if(pb<0)
		    {	
			printf("erorr!");
		    }
        	else if(pb ==0)
        	{
			ptext  = (char*)shmat(shmid,0,0);
			while(1)
			{
		
			           sleep(random()%10);
			           sem_a.sem_num = 0;
                       sem_a.sem_op = -1;
                       sem_a.sem_flg = SEM_UNDO;
                       semop(semid2, &sem_a, 1);
                       
                       sem_d.sem_num = 0;
                       sem_d.sem_op = -1;
                       sem_d.sem_flg = SEM_UNDO;
                       semop(semid4, &sem_d, 1);
           
			           printf("I am girl , get %s\n",ptext);
			
			           sem_d.sem_num = 0;
                       sem_d.sem_op = 1;
                       sem_d.sem_flg = SEM_UNDO;
                       semop(semid4, &sem_d, 1);
            
			           sem_b.sem_num = 0;
                       sem_b.sem_op = 1;
                       sem_b.sem_flg = SEM_UNDO;
                       semop(semid1, &sem_b, 1);
                       
			}
			
        	}
        	else
      		{
       		
       		          ptext  = (char*)shmat(shmid,0,0);
       		          while(1){
       		          sleep(random()%10);
       		          sem_c.sem_num = 0;
                      sem_c.sem_op = -1;
                      sem_c.sem_flg = SEM_UNDO;
                      semop(semid3, &sem_c, 1);
                       
                      sem_d.sem_num = 0;
                      sem_d.sem_op = -1;
                      sem_d.sem_flg = SEM_UNDO;
                      semop(semid4, &sem_d, 1);
                       
       		          printf("I am son get %s\n",ptext);
       		
       		          sem_d.sem_num = 0;
                      sem_d.sem_op = 1;
                      sem_d.sem_flg = SEM_UNDO;
                      semop(semid4, &sem_d, 1);
                       
       		          sem_b.sem_num = 0;
                      sem_b.sem_op = 1;
                      sem_b.sem_flg = SEM_UNDO;
                      semop(semid1, &sem_b, 1);}
       		
       	 }
       }
        else
        {
           ptext  = (char*)shmat(shmid,0,0);
           struct sembuf sem_b;
           int product;
           while(1){
           
           sleep(random()%10);
           sem_b.sem_num = 0;
           sem_b.sem_op = -1;
           sem_b.sem_flg = SEM_UNDO;
           semop(semid1, &sem_b, 1);
           
           sem_d.sem_num = 0;
           sem_d.sem_op = -1;
           sem_d.sem_flg = SEM_UNDO;
           semop(semid4, &sem_d, 1);
            
            
           product = random()%2;
           printf("Parent  put fruit %d\n",product);
           sprintf(ptext,"%d",product);
           if(product == 1)
           {printf("orange\n");
           
           sem_d.sem_num = 0;
           sem_d.sem_op = 1;
           sem_d.sem_flg = SEM_UNDO;
           semop(semid4, &sem_d, 1);
           
           sem_a.sem_num = 0;
           sem_a.sem_op = 1;
           sem_a.sem_flg = SEM_UNDO;
           semop(semid2, &sem_a, 1);
           } 
           else
           {
           printf("apple\n");
           
            sem_d.sem_num = 0;
            sem_d.sem_op = 1;
            sem_d.sem_flg = SEM_UNDO;
            semop(semid4, &sem_d, 1);
            
            sem_c.sem_op = 1;
            sem_c.sem_num = 0;
            sem_c.sem_flg = SEM_UNDO;
            semop(semid3,&sem_c,1 );
            }
           }
        }  
	return 0	;
	
}